Previous studies have shown that the serotonin-reuptake inhibitor (SSRI) fluoxetine affects neural progenitors derived from postnatal cerebellum or adult hippocampus and stimulates their proliferation. In the human cerebellum, the proliferation of cerebellar granule cells (CGC) continues until the 11th postnatal month and could be influenced in infants by breastfeeding-delivered SSRIs. Current information about fluoxetine effects on postnatal cerebellar neural progenitors is limited. Here we report the characterization of fluoxetine actions on rat postnatal cerebellar neural progenitors. RT-PCR and immunostaining revealed the expression of serotonin transporter (SERT), <em>5HT</em>(1A) receptors, tryptophan hydroxylase (TPH), and serotonin (<em>5HT</em>). Protracted in vitro fluoxetine treatment increased cell proliferation and differentiation. The proliferative effects of fluoxetine, <em>5HT</em>, and the selective agonist of <em>5HT</em>(1A) receptors trans-8-hydroxy-2-(N-n-propyl-N-3'-iodo-2'-propenyl)aminotetralin (8-OH-PIPAT) were abolished by the selective antagonist of <em>5HT</em>(1A) receptors, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide trihydrochloride (WAY-100635). Furthermore, fluoxetine-induced activation of both the cAMP-response element-binding (CREB) protein and extracellular signal-regulated protein kinases (ERK1/2), which was abolished by the selective inhibitor of MAP kinase kinase (MEK) 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), and increased cyclin D1 expression. All these effects were prevented by WAY-100635. Collectively, our results demonstrate that rat postnatal cerebellum contains neural progenitors capable of proliferating and differentiating in response to fluoxetine exposure, possibly through the activation of <em>5HT</em>(1A) receptors. The relevance of these findings for possible SSRI effects on the developing postnatal/infant human cerebellum should be explored.

The administration of 14 daily doses of cyproheptadine, BC-105, metergoline and methysergide induced a marked decrease in the number (Bmax) of 3H-spiroperidol binding sites (<em>5HT</em>2 sites) in frontal cortex, when assayed 48 h after the last dose; the apparent affinity (KD) of 3H-spiroperidol was not changed. The same treatment schedules failed to modify the KD and Bmax values for 3H-<em>5HT</em> binding to the <em>5HT</em>1 site in the hippocampus. Cyproheptadine, BC-105 and methysergide, but not metergoline, decreased the density of <em>5HT</em>2 sites in frontal cortex 48 h after a single dose. Additional studies of the decrease in 3H-spiroperidol binding after in vivo treatment with cyproheptadine showed that the extent of binding loss was unaltered by repeated washing. Furthermore, cyproheptadine added in vitro to membranes isolated from frontal cortex inhibited the binding of 3H-spiroperidol in a competitive manner; Scatchard plots were linear with the same maximum binding (Bmax) and different slopes. Therefore, these preliminary studies suggest that the loss of <em>5HT</em>2 binding sites after in vivo treatment with cyproheptadine and with other <em>5HT</em> antagonists may reflect an adaptive response. This apparent paradoxical effect suggests that the action of these drugs at the <em>5HT</em>2 binding sites should be reevaluated.

Serotonin (<em>5HT</em>) and norepinephrine (NE) produced long-lasting facilitation of glutamate-evoked activity of spinal motoneurons when applied iontophoretically with small ejection currents into the ventral horn. The facilitation was usually preceded by a brief period of inhibition at the onset of current application to the monoamine-containing barrels. This inhibition did not outlast the current application. Ejection of hydrogen ions produced only inhibition of glutamate-evoked activity with no subsequent facilitation at current offset. The <em>5HT</em> antagonists, methysergide and metergoline, blocked the facilitation, but not the inhibition of motoneuron excitability caused by <em>5HT</em>. Similarly, the alpha-adrenergic antagonists, piperoxane and phentolamine, blocked the facilitatory, but not the inhibitory, effects of NE on excitability of motoneurons. Since the inhibitory effects of <em>5HT</em> and NE could not be blocked with the antagonists used, and since ejection of hydrogen ions also produced inhibition, non-specific causes for the inhibitory effects of <em>5HT</em> and NE could not be rejected. However, the facilitatory effects of <em>5HT</em> and NE on excitability of motoneurons were readily blocked by antagonists and were, therefore, attributed to actions on separate <em>5HT</em> and NE receptors in the ventral horn.

1. The effects of serotonin (<em>5HT</em>) on neocortical pyramidal neurons were studied using whole cell and ON-cell patch-clamp recordings from acutely dissociated neurons. 2. <em>5HT</em> decreased high voltage-activated calcium channel currents in a dose-dependent and reversible manner in acutely dissociated neocortical pyramidal neurons. The maximum block was 30% of the peak whole cell current (at -10 mV). 3. The <em>5HT</em> modulation was mimicked by <em>5HT</em>1A agonists and was reduced by <em>5HT</em>1A antagonists. <em>5HT</em>2 antagonists had no effect on the modulation. These data suggest that the <em>5HT</em> effects were mediated by <em>5HT</em>1A receptors. 4. The <em>5HT</em>1A modulation was reduced in the presence of the specific N-type blocker omega-conotoxin GVIA (CgTx) and by the P-type channel blocker omega-agatoxin IVA (AgTx), but not by the L-type blocker nifedipine. <em>5HT</em> did not modulate the slowed tail currents in the presence of the dihydropyridine agonist Bay K 8644. These data suggest that N- and P-type channels (but not L-type channels) were targeted by <em>5HT</em>. 5. The modulation involved G proteins and utilized a membrane-delimited pathway. The modulation was rapid in onset (tau approximately 600 ms) and offset. About 50% of the reduction in current by <em>5HT</em>1A agonists was overcome by prepulses to 120 mV. 6. Slowing of current onset kinetics in response to <em>5HT</em>1A agonists was seen rarely in neocortical pyramidal neurons (11% of cases). The presence of slowing depended on agonist concentration, being evident only with high micromolar doses.

Suspensions of cells derived from the mesencephalic raphé or medullary raphé regions of the 13-14 day old embryonic rat brain were injected into the spinal cord of adult rats which had been previously denervated with 5,7-dihydroxytryptamine. At periods of up to 12 months after grafting, the spinal cords were taken for immunohistochemical analysis of 5-hydroxytryptamine (<em>5HT</em>), substance P (SP) and thyrotropin releasing hormone (TRH). In nearly all cases, surviving transplants were found. The grafts derived from mesencephalic raphé cells contained neurones which were immunoreactive to <em>5HT</em>, or SP, but not both together. On average 4% of the total possible number of the available embryonic mesencephalic serotoninergic cells were found. A very dense outgrowth of <em>5HT</em> positive fibres from the transplant was observed, extending up to 1.5 cm in both the caudal and rostral directions from the graft locus. Some SP immunoreactive fibres were also apparent near the implant. The grafts derived from the medullary transplant also contained <em>5HT</em>-immunoreactive cells, comprising on average 25% of the total <em>5HT</em> neurones available from the embryonic medullary primordium. In addition, neurones co-localizing <em>5HT</em> together with SP and TRH were visible, closely reflecting the situation found in the medullary raphé in situ. Dense plexi of fibres containing <em>5HT</em>-LI extended both caudally and rostrally up to 12-15 mm from the transplant. Outgrowth of SP and TRH varicose fibres was also demonstrable, although to a lesser degree than for <em>5HT</em>. It was also possible to find many motoneurones surrounded by varicose fibres containing both <em>5HT</em> and SP, in contrast to the situation with the mesencephalic grafts, where no such patterns of innervation were seen. The experiments indicate that the milieu of the spinal cord may compromise the survival of mesencephalic raphé <em>5HT</em> neurones far more than of medullary serotonin cells. However, despite this effect on cell survival, the outgrowth of fibres from the remaining mesencephalic <em>5HT</em> neurones was apparently unaffected by their ectopic position. Similarly, the transmitter content of both classes of raphé cells was largely unaltered, either by the transplantation process or by the environment into which they were placed. It is concluded that although the adult denervated spinal cord can selectively affect neuronal survival, it is incapable either of inducing in other serotoninergic cells placed within it the transmitter phenotype typical of medullary raphé neurones, or of causing those ectopically located <em>5HT</em> cells to form connections appropriate to the descending serotonin fibres.

Several voids exist in reliable positron emission tomography (PET) radioligands for quantification of the serotonin (<em>5HT</em>) receptor system. Even in cases where <em>5HT</em> radiotracers exist, challenges remain that have limited the utility of <em>5HT</em> imaging in clinical research. Herein we address an unmet need in <em>5HT</em>2a imaging using innovative chemistry. We report a scalable and robust synthesis of [(18)F]MDL100907, which was enabled by a Ni-mediated oxidative fluorination using [(18)F]fluoride. This first demonstration of a Ni-mediated fluorination used for PET imaging required development of a new reaction strategy that ultimately provided high specific activity [(18)F]MDL100907. Using the new synthetic strategy and optimized procedure, [(18)F]MDL100907 was evaluated against [(11)C]MDL100907 for reliability to quantify <em>5HT</em>₂a in the nonhuman primate brain and was found to be superior based on a single scan analysis using the same nonhuman primate. The use of this new <em>5HT</em>₂a radiotracer will afford clinical neuroscience research the ability to distinguish <em>5HT</em>₂a receptor abnormalities binding between healthy subjects and patients even when group differences are small.

The relative simplicity of the amphibian tadpole nervous system has been utilised as a model for the mechanisms underlying the generation and development of vertebrate locomotion. In this paper, we review evidence on the role of descending brainstem projections in the maturation and intrinsic modulation of tadpole spinal motor networks. Three transmitter systems that have been investigated utilise the biogenic amines serotonin (<em>5HT</em>) and noradrenaline (NA) and the inhibitory amino acid gamma-aminobutyric acid (GABA). The distribution, development and spinal targets of these systems will be reviewed. More recent data on the role of nitric oxide (NO) will also be discussed. This ubiquitous gaseous signalling molecule is known to play a crucial role in the developing nervous system, but until recently, had not been directly implicated in the brain regions involved in motor control. NO appears to be produced by three homologous brainstem clusters in the developing motor networks of two closely related amphibian species, Xenopus laevis and Rana temporaria but, surprisingly, it plays contrasting roles in these species. Given the presumed co-localisation and interaction of nitric oxide with conventional neurotransmitters, we discuss the potential relationship of nitrergic neurons with <em>5HT</em>, NA and GABA in these amphibian models.

The distribution of immunofluorescent somata and processes within the interpeduncular nucleus (IPN) containing substance P (SP), cholecystokinin (CCK), vasoactive intestinal peptide (VIP), somatostatin (SST), leu-enkephalin (L-ENK), dopamine beta hydroxylase (DBH), and serotonin (<em>5HT</em>) was examined in male rats treated with colchicine 48 hours prior to perfusion. Serial sections were examined for immunofluorescence and variations in the density of fluorescence rated 1 + (sparse) to 4 + (dense). The rostral subnucleus contained SP, SST, and L-ENK-positive somata and processes. Substance P and VIP processes were present throughout the rostral subnucleus but were concentrated in two ovoid areas located dorsally in the caudal region of this subnucleus. Cholecystokinin and L-ENK processes surrounded these ovoid areas. The entire width of the central subnucleus was crossed by SP and L-ENK processes oriented horizontally in narrow bands. Substance P processes were also aligned into vertical columns adjacent to the lateral margins of the central subnucleus. Leu-enkephalin and <em>5HT</em> processes were distributed throughout this subnucleus, while VIP processes were present only caudally. Dopamine beta hydroxylase processes were evenly distributed but were restricted from the vertical columns laterally. The intermediate subnuclei contained a sparse density of SP and <em>5HT</em> processes that were present in proximity to the major blood vessels penetrating this subnucleus. Only DBH processes were evenly distributed. The lateral subnuclei contained a dense concentration of SP processes. The medial edges of this subnucleus were distinguished by VIP, CCK, L-ENK, and <em>5HT</em> processes. The dorsal subnucleus contained <em>5HT</em>, L-ENK, and SST-positive somata and processes. Substance P, VIP, CCK, and DBH processes were also present. Dorsal-lateral subnuclei contained SP, SST, L-ENK, and DBH processes. Interstitial subnuclei contained SP, CCK, L-ENK, <em>5HT</em>, and DBH processes. This study demonstrates that perikarya and processes containing peptides and monoamines are distributed within subnuclei of IPN in a topographic and heterogeneous pattern. New features of IPN organization are revealed.

Synaptic strength can be highly variable from animal to animal within a species or over time within an individual. The process of synaptic plasticity induced by neuromodulatory agents might be unpredictable when the underlying circuits subject to modulation are themselves inherently variable. Serotonin (5-hydroxytryptomine; <em>5HT</em>) and serotonergic signaling pathways are important regulators of animal behavior and are pharmacological targets in a wide range of neurological disorders. We have examined the effect of <em>5HT</em> on electrical synapses possessing variable coupling strengths. While <em>5HT</em> decreased electrical coupling at synapses with weak electrical connectivity, synapses with strong electrical coupling were less affected by <em>5HT</em> treatment, as follows from the equations used for calculating coupling coefficients. The fact that the modulatory effect of <em>5HT</em> on electrical connections was negatively correlated with the strength of electrical coupling suggests that the degree of electrical coupling within a neural network impacts subsequent neuromodulation of those synapses. Biophysical studies indicated that these effects were primarily due to <em>5HT</em>-induced modulation of membrane currents that indirectly affect junctional coupling at synaptic contacts. In support of these experimental analyses, we created a simple model of coupled neurons to demonstrate that modulation of electrical coupling could be due solely to <em>5HT</em> effects on H-channel conductance. Therefore, variability in the strength of electrical coupling in neural circuits can determine the pharmacological effect of this neuromodulatory agent.

In the 1960s, serotonin (<em>5HT</em>) was associated with pulmonary arterial hypertension (PAH) caused by certain diet pills, but has recently been the subject of renewed interest in the field of PAH. Serotonin can be synthesised in the pulmonary endothelium with the rate-limiting step being the activity of tryptophan hydroxylase1 (Tph1). The serotonin is released and can then: (i) pass into the underlying pulmonary smooth muscle cells through the serotonin transporter (SERT) to initiate proliferation and/or (ii) activate serotonin receptors on pulmonary smooth muscle cells to evoke proliferation and/or contraction. Serotonin may also mediate pulmonary fibroblast proliferation via the SERT and/or serotonin receptors. Here we will unravel, discuss and update the 'serotonin hypothesis' of PAH in light of recent advances in the field. In conclusion, the activity of serotonin receptors, the SERT and Tph1 can all be elevated in clinical and experimental PAH and each offers a potentially unique therapeutic target.

1. [(3)H]D,L-5-hydroxytryptophan ([(3)H]<em>5HT</em>P) was injected under pressure into cell bodies of identified cholinergic and serotonergic neurones in the central nervous system of the marine mollusc, Aplysia californica.2. Both serotonergic and cholinergic neurones converted [(3)H]<em>5HT</em>P to [(3)H]5-hydroxytryptamine ([(3)H]<em>5HT</em>).3. The fate of [(3)H]<em>5HT</em> in the two types of neurones differed. In serotonergic cells, <em>5HT</em> was present primarily in particulate form; the transmitter readily moved from cell bodies into nerves by selective transport. In contrast, <em>5HT</em> remained free in the cytoplasm of the cholinergic neurone, and was not transported from the cell body.4. Treatment of Aplysia with reserpine decreased the proportion of [(3)H]<em>5HT</em> associated with particulate material, and also decreased the amount of [(3)H]<em>5HT</em> recovered.5. Serotonergic neurones possess specific mechanisms for the storage and axonal transport of <em>5HT</em> which are absent in cholinergic cells.

5-Hydroxytryptamine (<em>5HT</em>)1C and <em>5HT</em>2 receptors appear to be closely related, from a molecular viewpoint, displaying similar second messenger systems and a high degree of sequence homology. However, there are striking differences in the interactions of <em>5HT</em> with <em>5HT</em>1C and <em>5HT</em>2 receptors; <em>5HT</em> is generally more potent in stimulating responses mediated through <em>5HT</em>1C receptors than responses mediated through <em>5HT</em>2 receptors. Also [3H]<em>5HT</em> labels <em>5HT</em>1C receptors and not <em>5HT</em>2 receptors. In order to explore more fully the molecular rationale for these differences, radioligand binding studies were performed in rat, human, and porcine brain and choroid plexus tissues and in mammalian cells transfected with rat <em>5HT</em>1C or <em>5HT</em>2 receptors; second messenger studies (inositol phosphate accumulation) were performed in the transfected cells. The second messenger studies confirmed the approximately 10-fold higher potency of <em>5HT</em> in stimulating intracellular responses through <em>5HT</em>1C receptors (EC50 = 8.3 nM) than in stimulating intracellular responses through <em>5HT</em>2 receptors (EC50 = 101 nM). An agonist radioligand selective for the <em>5HT</em>1C and <em>5HT</em>2 receptors, 2,5-dimethoxy-(4-[125I]iodo)phenylisopropylamine, was used, as well as [3H]<em>5HT</em>, [3H]mesulergine (antagonist radioligand for <em>5HT</em>1C receptors), and [3H]ketanserin (antagonist radioligand for <em>5HT</em>2 receptors). Computer-assisted analyses of the binding data revealed two agonist affinity states for the <em>5HT</em>1C receptor. The agonist high affinity state of the receptor was modifiable by guanyl nucleotides. The proportion of agonist high affinity states, relative to the total receptor population, was approximately 10% for both receptors. The apparent higher affinity of <em>5HT</em> for the radiolabeled <em>5HT</em>1C receptors was due to the higher affinity <em>5HT</em> displayed for the agonist low affinity state of the <em>5HT</em>1C receptor, compared with the affinity of <em>5HT</em> for the agonist low affinity state of the <em>5HT</em>2 receptor. The correspondence between the higher affinity of <em>5HT</em> for the agonist low affinity state of the <em>5HT</em>1C receptor, relative to the <em>5HT</em>2 receptor, and the higher potency of <em>5HT</em> in stimulating <em>5HT</em>1C responses indicates that <em>5HT</em> interacts with the agonist low affinity state of the <em>5HT</em>1C and <em>5HT</em>2 receptors in initiating its biological effects. These observations indicate that guanine nucleotide-binding protein (G protein)-coupled receptors can exhibit high affinity for neurotransmitters in both the free receptor and the G protein-coupled states and that receptors exhibiting this property may represent a novel subfamily of G protein-coupled receptors.

The taxa Nemertodermatida and Acoela have traditionally been considered closely related and classified as sister groups within the Acoelomorpha Ehlers 1984 (Platyhelminthes). Recent molecular investigations have questioned their respective position. In this study, the 5-HT and FMRFamide immunoreactivity (IR) in the nervous system of two nemertodermatids, Nemertoderma westbladi and Meara stichopi, is described. The 5-HT immunoreactive pattern differs in the two nemertodermatids studied. In M. stichopi, two loose longitudinal bundles of 5-HT-immunoreactive fibres and an basi-epidermal nerve net were observed. In N. westbladi the 5-HT-IR shows a ring-shaped commissural structure, different from the commissural brain of acoels. In both nemertodermatids, FMRFamide immunoreactive nerve fibres followed the 5-HT-immunoreactive fibres. It is demonstrated that the Nemertodermatida have neither a 'commissural brain' structure similar to that of the Acoela, nor a 'true', ganglionic brain and orthogon, typical for other Platyhelminthes. The question of the plesiomorphic or apomorphic nature of the nervous system in Nemertodermatida cannot yet be answered. The neuroanatomy of the studied worms provides no synapomorphy supporting the taxon Acoelomorpha.

The depolarisation-induced release of brain-derived neurotrophic factor (BDNF) from adult rat striatal slices was studied in vitro. The slices were preloaded with [125I]BDNF and exposed to depolarising stimulation with varying concentrations of veratrine (up to 50 microM) and potassium (up to 50 mM) which caused activity-dependent short-term release of [125I]BDNF. The results indicate that this stimulated release of [125I]BDNF is not regulated by a feedback mechanism mediated via the TrkB receptor. The release of [125I]BDNF was found to be dependent on the concentrations of both extracellular and intracellular calcium, since BDNF release was modulated by the addition of both EGTA and BAPTA-AM, agents chelating either external or internal Ca(2+), respectively. BDNF release also proved to be dependent on activation of IP(3) mediated Ca(2+) release from intracellular stores. [125I]BDNF release was also modulated by <em>5HT</em>(3) receptor ligands and by receptors coupled to adenylate cyclase. Taken together, these results indicate that [125I]BDNF release is activity dependent, and is modulated by changes in Ca(2+) levels. Moreover the release occurs via a mechanism involving cAMP.

Spinal cord injury (SCI) is a debilitating disorder, which produces profound deficits in volitional motor control. Following medical stabilization, recovery from SCI typically involves long term rehabilitation. While recovery of walking ability is a primary goal in many patients early after injury, those with a motor incomplete SCI, indicating partial preservation of volitional control, may have the sufficient residual descending pathways necessary to attain this goal. However, despite physical interventions, motor impairments including weakness, and the manifestation of abnormal involuntary reflex activity, called spasticity or spasms, are thought to contribute to reduced walking recovery. Doctrinaire thought suggests that remediation of this abnormal motor reflexes associated with SCI will produce functional benefits to the patient. For example, physicians and therapists will provide specific pharmacological or physical interventions directed towards reducing spasticity or spasms, although there continues to be little empirical data suggesting that these strategies improve walking ability. In the past few decades, accumulating data has suggested that specific neuromodulatory agents, including agents which mimic or facilitate the actions of the monoamines, including serotonin (<em>5HT</em>) and norepinephrine (NE), can initiate or augment walking behaviors in animal models of SCI. Interestingly, many of these agents, particularly <em>5HT</em>ergic agonists, can markedly increase spinal excitability, which in turn also increases reflex activity in these animals. Counterintuitive to traditional theories of recovery following human SCI, the empirical evidence from basic science experiments suggest that this reflex hyper excitability and generation of locomotor behaviors are driven in parallel by neuromodulatory inputs (<em>5HT</em>) and may be necessary for functional recovery following SCI. The application of this novel concept derived from basic scientific studies to promote recovery following human SCI would appear to be seamless, although the direct translation of the findings can be extremely challenging. Specifically, in the animal models, an implanted catheter facilitates delivery of very specific <em>5HT</em> agonist compounds directly onto the spinal circuitry. The translation of this technique to humans is hindered by the lack of specific surgical techniques or available pharmacological agents directed towards <em>5HT</em> receptor subtypes that are safe and effective for human clinical trials. However, oral administration of commonly available <em>5HT</em>ergic agents, such as selective serotonin reuptake inhibitors (SSRIs), may be a viable option to increase central <em>5HT</em> concentrations in order to facilitate walking recovery in humans. Systematic quantification of how these SSRIs modulate human motor behaviors following SCI, with a specific focus on strength, reflexes, and the recovery of walking ability, are missing. This video demonstration is a progressive attempt to systematically and quantitatively assess the modulation of reflex activity, volitional strength and ambulation following the acute oral administration of an SSRI in human SCI. Agents are applied on single days to assess the immediate effects on motor function in this patient population, with long-term studies involving repeated drug administration combined with intensive physical interventions.

The role of the monoamines dopamine (DA) and serotonin (<em>5HT</em>) and the monoamine-metabolizing enzyme monoamine oxidase A (MAOA) have been repeatedly implicated in studies of alcohol use and dependence. Genetic investigations of MAOA have yielded conflicting associations between a common polymorphism (MAOA-LPR) and risk for alcohol abuse. The present study provides direct comparison of tissue-specific MAOA expression and the level of alcohol consumption. We analyzed rhesus macaque MAOA (rhMAOA) expression in blood from males before and after 12 months of alcohol self-administration. In addition, nucleus accumbens core (NAc core) and cerebrospinal fluid (CSF) were collected from alcohol access and control (no alcohol access) subjects at the 12-month time point for comparison. The rhMAOA expression level in the blood of alcohol-naive subjects was negatively correlated with subsequent alcohol consumption level. The mRNA expression was independent of rhMAOA-LPR genotype and global promoter methylation. After 12 months of alcohol use, blood rhMAOA expression had decreased in an alcohol dose-dependent manner. Also after 12 months, rhMAOA expression in the NAc core was significantly lower in the heavy drinkers, as compared with control subjects. The CSF measured higher levels of DA and lower DOPAC/DA ratios among the heavy drinkers at the same time point. These results provide novel evidence that blood MAOA expression predicts alcohol consumption and that heavy alcohol use is linked to low MAOA expression in both the blood and NAc core. Together, the findings suggest a mechanistic link between dampened MAOA expression, elevated DA and alcohol abuse.

The dependence of platelet-<em>5HT</em> content on apparent kinetic parameters of <em>5HT</em> uptake was analyzed in 56 healthy subjects and 47 depressed patients, who had not been taking psychotropic medication for several months. There were no significant relationships between apparent Vmax or Km and platelet-<em>5HT</em> content in both groups. However, the ratio of Vmax to Km, as a measure of apparent <em>5HT</em> uptake efficiency, significantly correlated with the platelet-<em>5HT</em> concentration in healthy subjects (r=0.627 p<0.001). Female controls showed a higher correlation coefficient (r=0.723) than male controls (r=0.457). A marked deviation from the linear relationship between <em>5HT</em> content and the ratio Vmax/K was observed in female depressed patients (r=0.250 n.s.). In male depressed patients the correlation coefficient (r=0.485 p<0.05) was similar to male healthy subjects, but the regression equations differed significantly in slope and intercept. Dividing controls and patients in subgroups with low, median and high net uptake rates, it was found that the frequencies of these uptake rate classes were 24.6%, 33.3%, 42.1% in controls and 38.3%, 44.7%, 17.0% in patients respectively. Patients and controls with low net uptake rate showed very similar uptake kinetics and uptake efficiencies, but the lack of a significant correlation between <em>5HT</em> content and the ratio Vmax/Km differentiated patients from controls. The status of the serotonergic system, expressed as relationship between <em>5HT</em> content and uptake efficiency, was very similar in patients and controls in the range of medium net uptake rate. A trend toward higher values of uptake efficiency was apparent in patients with high net uptake rate but the platelet-<em>5HT</em> content was similar to corresponding controls. Mean scores on the HAMD scale (total score and psychic anxiety item) were significantly higher in the low net uptake rate group of patients than in those with a high net uptake rate.

In this study, we have identified and characterized 5-HT3-like receptors in the rat medial prefrontal cortex (mPFc), an area with a moderate density of 5-HT3 binding sites, using the techniques of single unit recording and microiontophoresis. The microiontophoresis of the 5-HT3 receptor agonist 2-methylserotonin (2-Me-<em>5HT</em>), similar to the action of 5-HT, produced a current-dependent (10-80 nA) suppression of the firing rate of both spontaneously active and glutamate (GLU)-activated (quiescent) mPFc cells. Phenylbiguanide (PBG), another 5-HT3 receptor agonist, suppressed the firing rate of mPFc cells but was less effective compared to 2-Me-<em>5HT</em>. The continuous iontophoresis (10-20 min) of 1 M magnesium chloride markedly attenuated the suppressant effect produced by electrical stimulation of the ascending 5-HT pathway, but did not alter 2-Me-<em>5HT</em>'s action, suggesting that the action of 2-Me-<em>5HT</em> is a direct one. The suppressant action of 2-Me-<em>5HT</em> on mPFc cells was blocked by a number of structurally diverse and selective 5-HT3 antagonists, with a rank order of effectiveness as follows: ICS 205930 = (+/-)-zacopride greater than granisetron = ondansetron = LY 278584 greater than MDL 72222. Furthermore, the intravenous administration of (+/-)-zacopride antagonized the action of 2-Me-<em>5HT</em> and PBG on mPFc cells. In contrast to the effects of the 5-HT3 receptors antagonists, other receptor antagonists such as metergoline (5-HT1A,1B,1C.2), (+/-)-pindolol (5-HT1A,1B, beta), SCH 23390 (5-HT1C.2, D1), l-sulpiride (D2) or SR 95103 (GABAA) failed to block 2-Me-<em>5HT</em>'s action. These results combined suggest that 2-Me-<em>5HT</em>'s suppressive action on mPFc cells is mediated directly by 5-HT3-like receptors.

The uptake and metabolism of 5-hydroxytryptamine (<em>5HT</em>) and l-norepinephrine (NE) were measured in endothelial cells of pig pulmonary artery and aorta, as well as in lung slices. Evidence for oxidative deamination and for a saturable uptake mechanism, sensitive to cold, imipramine, and NA+-free medium was obtained for <em>5HT</em> in lung slices and in the pulmonary as well as in the aortic endothelium, separated from the lumen by absorption to Millipore filters or by exposure to collagenase. For NE, however, a similar type of uptake could be deomonstrated in lung slices only. In the aortic and pulmonary endothelium, NE was metabolized, but its uptake was not influenced by imipramine, Na+-free medium, and high substrate concentration. The aortic and pulmonary endothelium have, therefore, similar properties and exhibit for <em>5HT</em>, but not for NE, a type of uptake similar to that existing in lung capillaries.

The subcellular distribution of basic substances such as mepacrine, chloroquine, chlorpromazine and imipramine was studied in rabbit blood platelets exposed to these compounds in vitro and to some in vivo. All the drugs showed a preferential concentration in the 5-hydroxytryptamine (<em>5HT</em>) storage organelles (<em>5HT</em> vesicles). Chloroquine and mepacrine accumulated more specifically in the organelles than did chlorpromazine and imipramine. After osmotic shock of the <em>5HT</em> vesicles chlorpromazine sedimented mostly with the vesicular membranes, whereas the other compounds preferentially went into the supernatant. It is concluded that (a) fluorescent basic compounds such as mepacrine are rather specific markers for the <em>5HT</em> storage organelles in live platelets and (b) drugs such as chlorpromazine and imipramine also have a considerable affinity for these organelles.

1 Dopamine deficiency in the brain is the prime biochemical deficit in Parkinson's disease, but loss of noradrenaline and <em>5HT</em> also may contribute. 2 In rats, <em>5HT</em>-containing neurones originating from the dorsal and median raphe nuclei innervate forebrain dopamine-containing areas so as to impose an inhibitory regulatory tone on dopamine function. However, this interaction between brain dopamine and <em>5HT</em>-containing neuronal systems is complex, and the effect produced appears dependent on the relative activity of each system. 3 Anatomical evidence for innervation of dopamine-containing brain regions by noradrenaline fibres in the rat is scanty, but functional studies suggest the existence of inputs which facilitate dopamine function. 4 Drug therapy designed to increase or decrease brain <em>5HT</em> function has had no consistent effect in Parkinson's disease. 5 Manipulation of brain noradrenergic activity in Parkinson's disease had little effect, although the noradrenaline precursor L-threo-DOPS may reduce freezing attacks. 6 Until more specific drug molecules are available the role of brain noradrenergic and <em>5HT</em> mechanisms in Parkinson's disease remains uncertain.

Continuous exposure of non-parturient rats to pups can induce maternal behavior similar in most aspects to that found in the postpartum rat. Surprisingly, young juvenile rats (20-24 days of age) only require 1-3 days of exposure to pups, while adults require 4-8 days before maternal behavior emerges. Dopamine (DA) and possibly serotonin (5-HT) may mediate the expression of adult maternal behavior. We hypothesize that postnatal changes in DA and 5-HT within the neural circuit that supports maternal behavior including the medial preoptic area (MPOA), medial and cortical amygdala (MCA), and nucleus accumbens (NAC), may underlie these differences in responsiveness across juveniles and adults. We measured DA, 5-HT, and their metabolites in postmortem samples of these regions in maternal and non-maternal juvenile and adult females. The only difference found across behavioral groups was that the MPOA of adults induced into maternal behavior by pup exposure had more DA than did that of isolated adult females or maternal juveniles. However, when adults versus juveniles were compared, the content of DA and 3,4-dihydroxyphenylacetic (DOPAC) was higher in the adult than in the juvenile NAC and MCA; the content of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in these structures did not vary across the age groups. In contrast, higher levels of 5-HT and 5-HIAA were found in the MPOA in juveniles compared to adults. We propose that these region-specific age differences in DA and <em>5HT</em> may underlie differences in juvenile-adult responses to pups.

This study examined whether activation of <em>5HT</em>(1B) receptors in the rodent globus pallidus (GP) could reduce GABA release in vitro and reverse reserpine-induced akinesia in vivo. Microdissected slices of GP from male Sprague Dawley rats (300-350 g) were preloaded with [(3)H]-GABA. During subsequent superfusion, 4 min fractions were collected for analysis of release. The effects of the <em>5HT</em>(1B) receptor agonist, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3, 2-b]pyrid-5-one (CP-93129), on 25 mM KCl-evoked release were examined using a standard dual stimulation paradigm. Male Sprague Dawley rats (270 - 290 g), stereotaxically cannulated above the GP, were rendered akinetic by injection of reserpine (5 mg kg(-1) s.c.). Eighteen hours later, the rotational behaviour induced by unilateral injection of CP-93129 was examined. CP-93129 (0.6-16.2 microM) produced a concentration-dependent inhibition of 25 mM KCl-evoked [(3)H]-GABA release reaching a maximum inhibition of 52.5+/-4.5%. The effect of a submaximal concentration of CP-93129 (5.4 microM) was fully inhibited by the <em>5HT</em>(1B) receptor antagonist, isamoltane (10 microM). Following intrapallidal injection, CP-93129 (30-330 nmol in 0.5 microl) produced a dose-dependent increase in net contraversive rotations reaching a maximum of 197+/-32 rotations in 240 min at 330 nmol. Pre-treatment with isamoltane (10 nmol in 1 microl) inhibited the effects of a submaximal dose of CP-93129 (220 nmol) by 84+/-6%. These data suggest that at least some <em>5HT</em>(1B) receptor function as heteroreceptors in the GP, reducing the release of GABA. Moreover, CP-93129-mediated activation of these receptors in the GP provides relief of akinesia in the reserpine-treated rat model of PD.

The effects of combined microinjection into the nucleus ambiguus (NA) of dopamine (DA) and the 5-hydroxytryptamine-1A (<em>5HT</em>-1A) receptor agonist 8-hydroxy-2-[di-n-propylamino]tetralin (8-OH-DPAT) on arterial pressure (AP) and heart rate (HR) were studied in 24 urethane-anaesthetized, artificially ventilated spinal (C1) rats. Sites from which bradycardia was elicited by microinjection of L-glutamate (GLU) were selected for microinjection of DA and 8-OH-DPAT into the NA. Microinjections of 8-OH-DPAT (60-300 pmol in 10 nl) elicited a dose-dependent bradycardia; the HR responses elicited by microinjection of 300 pmol of 8-OH-DPAT were significantly larger (-34.0 +/- 3.0) than responses elicited by the threshold dose of 60 pmol (-3.1 +/- 0.1 bpm). The onset latency of the HR responses elicited by the 300 pmol of 8-OH-DPAT was 6.5 +/- 0.5 s and the peak was reached in 40.0 +/- 8.0 s. The duration of these responses was 615 +/- 3.5 s. Microinjection of DA (1 nmol in 10 nl) within 3-5 s from the time of 8-OH-DPAT microinjection (60 pmol in 2 nl) into the NA at sites previously shown to elicit decreases in HR following microinjection of GLU, produced significant additive effects in eliciting bradycardia (20.4 +/- 2.9 bpm) when compared with decreases in HR elicited by microinjection of DA (11.1 +/- 1.8 bpm) or of 8-OH-DPAT (3.1 +/- 0.1 bpm) alone. There were no changes in AP after microinjections of DA, 8-OH-DPAT or of these two substances combined.(ABSTRACT TRUNCATED AT 250 WORDS)