BACKGROUND

A promoter polymorphism in the serotonin transporter (<em>5HT</em>TLPR) has functional effects on an important physiologic process involved in serotonin (<em>5HT</em>) signaling. Despite the fact that variation in the <em>5HT</em> system has long been implicated in the etiology of aggressive behaviors, only a few association-based studies with mixed results have been reported.

METHODS

We conducted family-based tests of association in a sample of 366 families from which 1187 genotypes of the <em>5HT</em>TLPR were generated using polymerase chain reaction. Ratings of aggressive behavior were obtained from parents and teachers longitudinally using the Child Behavior Checklist (CBCL) and Teacher Report Form (TRF), instruments widely used in behavioral and psychiatric genetics.

RESULTS

Within-family tests suggest an association between the s-allele of the <em>5HT</em>TLPR and higher aggressive behavior in middle childhood. The strongest association was at age 9 and for an aggregate measure of teacher-rated aggressive behavior.

CONCLUSIONS

This is the first report of an association analysis of the <em>5HT</em>TLPR in a general population sample of school-age children. The results provide some support for the hypothesis that the functional effects of the <em>5HT</em>TLPR s-allele are associated with higher levels of aggressive behavior in middle childhood.

The effects of serotoninergic and noradrenergic drugs (applied intrathecally) on treadmill locomotion were evaluated in two adult cats subjected to a ventral and ventrolateral spinal lesion (T13). Despite the extensive spinal lesion, severely damaging important descending pathways such as the reticulo- and vestibulospinal tracts, both cats recovered quadrupedal voluntary locomotion. As detailed in a previous paper, the locomotor recovery occurred in three stages defined as early period, when the animal could not walk with its hindlimbs, recovery period, when progressive improvement occurred, and plateau period, when a more stable locomotor performance was observed. At this latter stage, the cats suffered from postural and locomotor deficits, such as poor lateral stability, irregular stepping of the hindlimbs, and inconsistent homolateral fore- and hindlimb coupling. The present study aimed at evaluating the potential of serotoninergic and/or noradrenergic drugs to improve the locomotor abilities in the early and late stages. Both cats were implanted chronically with an intrathecal cannula and electromyographic (EMG) electrodes, which allowed determination, under similar recording conditions, of the locomotor performance pre- and postlesion and comparisons of the effects of different drugs. EMG and kinematic analyses showed that norepinephrine (NE) injected in early and plateau periods improved the regularity of the hindlimb stepping and stabilized the interlimb coupling, permitting to maintain constant locomotion for longer periods of time. Methoxamine, the alpha1-agonist (tested only at the plateau period), had similar effects. In contrast, the alpha2-agonist, clonidine, deteriorated walking. Serotoninergic drugs, such as the neurotransmitter itself, serotonin (<em>5HT</em>), the precursor 5-hydroxytryptophan (<em>5HT</em>P), and the agonist quipazine improved the locomotion by increasing regularity of the hindlimb stepping and by increasing the step cycle duration. In contrast, the <em>5HT</em>1A agonist 8-hydroxy-dipropylaminotetralin (DPAT) caused foot drag in one of the cats, resulting in frequent stumbling. Injection of combination of methoxamine and quipazine resulted in maintained, regular stepping with smooth movements and good lateral stability. Our results show that the effects of drugs can be integrated to the residual voluntary locomotion and improve some of its postural aspects. However, this work shows clearly that the effects of drugs (such as clonidine) may depend on whether or not the spinal lesion is complete. In a clinical context, this may suggest that different classes of drugs could be used in patients with different types of spinal cord injuries. Possible mechanisms underlying the effect of noradrenergic and serotoninergic drugs on the locomotion after partial spinal lesions are discussed.

Chlorpyrifos (CPF), one of the most widely-used organophosphate pesticides, is a suspected neuroteratogen. We administered CPF to neonatal rats on postnatal days (PN) 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), treatments devoid of overt toxicity. At the end of the treatment period (PN5 and 15, respectively) and 5-7 days later, we then examined the effects on paroxetine (PXT) binding to the presynaptic <em>5HT</em> high-affinity transporter, a marker for serotonin (<em>5HT</em>) projections. In males, we found a persistent decrease in PXT binding across the two different treatment regimens, with deficits apparent in a brain region containing <em>5HT</em> terminal fields (forebrain) as well as in a region containing <em>5HT</em> cell bodies (brainstem). In contrast, females given the early treatment regimen (PN1-4) showed deficits in the brainstem but transient elevations in the forebrain; the later treatment regimen (PN11-14) had no significant effect on PXT binding in females. These data are consistent with earlier work showing brainstem cell injury resulting from neonatal CPF exposure, and indicate specific damage to <em>5HT</em> neurons, with a consequent loss of transporter expression in both terminal fields and perikarya. In females, the damage may be temporarily offset by initial trophic effects in the terminal region, consequent to the cholinergic stimulation evoked by cholinesterase inhibition via the active metabolite, CPF oxon. The gender-selective effects on <em>5HT</em> systems are likely to contribute to similar gender dimorphism in behavioral performance. Because the CPF effects involve <em>5HT</em>, a neurotransmitter intimately involved in the control of mood, we suggest the need to evaluate behaviors that typify animal models of depression.

The serotonin (<em>5HT</em>1A) receptor subtype is one member of the <em>5HT</em>1 receptor family and is constitutively expressed on Jurkat cells and is elevated on human T lymphocytes after mitogenic activation. Published reports show that human T lymphocytes and monocytes also release <em>5HT</em> after stimulation with PHA or IFN-gamma. In lymphocytes and the central nervous system, the <em>5HT</em>1A receptor is coupled to regulation of adenylate cyclase. The <em>5HT</em>1A receptor agonists inhibit activation of adenylate cyclase. The purpose of the experiments reported here was to investigate further the role <em>5HT</em> and the <em>5HT</em>1A receptor may play in the regulation of human and murine T cell activity. For this purpose, human PBMC or murine spleen cells were used for experimental purposes rather than Jurkat cells. The results show that inhibition of <em>5HT</em> synthesis inhibits IL-2-stimulated human T cell proliferation and that addition of 5-hydroxytryptophan, a precursor of <em>5HT</em>, reverses inhibition of T cell proliferation. The <em>5HT</em>1 receptor antagonist, metitepine, and the <em>5HT</em>1A selective antagonist, pindobind-<em>5HT</em>1A, also block T cell proliferation. Inhibition by metitepine is reversed by <em>5HT</em> and by the selective <em>5HT</em>1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) (8-OH-DPAT). Selective <em>5HT</em>1A receptor antagonists cause elevation of cAMP in human T cells. In a murine model, selective <em>5HT</em>1A receptor antagonists inhibit contact sensitivity responses but not Ab responses to oxazalone in vivo. Inhibition is reversed by 8-OH-DPAT. In addition, production of Th1 cytokines, such as IL-2 and IFN-gamma, by Ag-stimulated, immune murine spleen cells is inhibited by <em>5HT</em>1A receptor antagonists in vitro but not by <em>5HT</em>1C/2 receptor antagonists.

The effects of oleamide, an amidated lipid isolated from the cerebrospinal fluid of sleep-deprived cats, on serotonin receptor-mediated responses were investigated in cultured mammalian cells. In rat P11 cells, which endogenously express the 5-hydroxytryptamine2A (<em>5HT</em>2A) receptor, oleamide significantly potentiated <em>5HT</em>-induced phosphoinositide hydrolysis. In HeLa cells expressing the <em>5HT</em>7 receptor subtype, oleamide caused a concentration-dependent increase in cAMP accumulation but with lower efficacy than that observed by <em>5HT</em>. This effect was not observed in untransfected HeLa cells. Clozapine did not prevent the increase in cAMP elicited by oleamide, and ketanserin caused an approximately 65% decrease. In the presence of <em>5HT</em>, oleamide had the opposite effect on cAMP, causing insurmountable antagonism of the concentration-effect curve to <em>5HT</em>, but had no effect on cAMP levels elicited by isoproterenol or forskolin. These results indicate that oleamide can modulate <em>5HT</em>-mediated signal transduction at different subtypes of mammalian <em>5HT</em> receptors. Additionally, our data indicate that oleamide acts at an apparent allosteric site on the <em>5HT</em>7 receptor and elicits functional responses via activation of this site. This represents a unique mechanism of activation for <em>5HT</em> G protein-coupled receptors and suggests that G protein-coupled neurotransmitter receptors may act like their iontropic counterparts (i.e., gamma-aminobutyric acid type A receptors) in that there may be several binding sites on the receptor that regulate functional activity with varying efficacies.

This study mapped the location of serotonin (<em>5HT</em>) 1A, 2A and 2C receptor mRNA expression in the female macaque hypothalamus and determined whether the expression was regulated by estrogen plus or minus progesterone treatment using in situ hybridization (ISH) and densitometric analysis of autoradiographic films. The experimental groups of pigtail macaques (Macaca nemestrina) were spayed controls (n=4), estrogen treated (28 days, n=4) and estrogen+progesterone-treated animals (14 days estrogen+14 days estrogen and progesterone, n=4). Monkey specific <em>5HT</em>1A (432 bp), 2A (411 bp) and 2C (294 bp) receptor probes were generated with PCR. Moderate <em>5HT</em>1A receptor hybridization signal was detected in the preoptic area and the ventromedial nuclei. Less intense <em>5HT</em>1A receptor signal was detected in a contiguous area from the dorsomedial nuclei through the posterior hypothalamus and in the supramammillary area. There was no change in <em>5HT</em>1A receptor hybridization signal in any area with ovarian steroid treatment. Dense <em>5HT</em>2A receptor hybridization signal was morphologically confined to the paraventricular, supraoptic, and mammillary nuclei and the external capsule of the thalamus. Light <em>5HT</em>2A mRNA signal was inconsistently observed in the ventromedial nuclei. There was no change in the <em>5HT</em>2A receptor hybridization signal in any area with ovarian steroid treatment. The <em>5HT</em>2C receptor mRNA was widely distributed in the macaque hypothalamus. The preoptic area and anterior hypothalamus were largely positive for <em>5HT</em>2C mRNA with a more concentrated signal in a narrow periventricular area. Dense <em>5HT</em>2C receptor signal was detected lateral to the ventromedial nuclei (capsule), in the tuberomammillary nuclei, arcuate nucleus, dorsomedial nuclei, infundibular area and choroid plexus. Moderate <em>5HT</em>2C receptor signal was detected in the ventromedial nuclei, lateral hypothalamus and dorsal to posterior hypothalamus. There was a significant decrease in total <em>5HT</em>2C mRNA hybridization signal with ovarian steroid treatment in the ventromedial nuclei, dorsal and posterior hypothalamus. In summary, macaque <em>5HT</em>1A, 2A and 2C receptor mRNAs are located in distinct hypothalamic loci which play a role in a number of autonomic functions and behavior. Ovarian steroids decreased the expression of <em>5HT</em>2C receptor mRNA in the ventromedial nuclei, dorsal and posterior hypothalamus. The expression of <em>5HT</em>1A and <em>5HT</em>2A receptor mRNA was not altered by treatment with ovarian steroids.

We tested the hypothesis that the <em>5HT</em>(1D)R, the primary antinociceptive target of triptans, is differentially distributed in tissues responsible for migraine pain. The density of <em>5HT</em>(1D)R was quantified in tissues obtained from adult female rats with Western blot analysis. Receptor location was assessed with immunohistochemistry. The density of <em>5HT</em>(1D)R was significantly greater in tissues known to produce migraine-like pain (i.e. circle of Willis and dura) than in structures in which triptans have no antinociceptive efficacy (i.e. temporalis muscle). <em>5HT</em>(1D)R-like immunoreactivity was restricted to neuronal fibres, where it colocalized with calcitonin gene-related peptide and tyrosine hydroxylase immunoreactive fibres. These results are consistent with our hypothesis that the limited therapeutic profile of triptans could reflect its differential peripheral distribution and that the antinociceptive efficacy reflects inhibition of neuropeptide release from sensory afferents. An additional site of action at sympathetic efferents is also suggested.

Serotonin (5-hydroxytryptamine: <em>5HT</em>) is an important neuroactive substance in the model roundworm, Caenorhabditis elegans. Aside from having effects in feeding and egg-laying, <em>5HT</em> inhibits motility and also modulates several locomotory behaviors, notably food-induced slowing and foraging. Recent evidence showed that a serotonergic <em>5HT</em>2-like receptor named SER-1 (also known as <em>5HT</em>2ce) was responsible for the effect of <em>5HT</em> on egg-laying. Here we confirm this observation and show that SER-1 also plays an important role in locomotion. A mutant lacking SER-1 was found to be highly resistant to exogenous <em>5HT</em> in the absence of food and this resistant phenotype was rescued by reintroducing the SER-1 gene in a mutant background. Pharmacological studies showed that the same antagonists that blocked the activity of recombinant SER-1 in vitro also inhibited the effect of <em>5HT</em> on motility, suggesting the same receptor was responsible for both effects. When tested for locomotory behaviors, the SER-1 mutant was found to be moderately defective in food-induced slowing. In addition, the mutant changed direction more frequently than the wildtype when searching for food, suggesting that SER-1 may play a role in navigational control during foraging. Both these effects required the presence of MOD-1, a <em>5HT</em> gated chloride channel, and the results indicate that SER-1 and MOD-1 modulate these behaviors through a common pathway. On the basis of expression analysis of a ser-1::GFP translational fusion, SER-1 is prominently located in central, integrating neurons of the head ganglia (RIA and RIC) but not the body wall musculature. The evidence suggests that SER-1 controls locomotion through indirect modulation of neuromuscular circuits and has effects both on speed and direction of movement.

Developmental exposure to unrelated neurotoxicants can nevertheless produce similar neurobehavioral outcomes. We examined the effects of developmental exposure to terbutaline, a tocolytic beta2-adrenoceptor agonist used to arrest preterm labor, and chlorpyrifos (CPF), a widely used organophosphate pesticide, on serotonin (<em>5HT</em>) systems. Treatments were chosen to parallel periods typical of human developmental exposures, terbutaline (10 mg/kg) on postnatal days (PN) 2-5 and CPF (5 mg/kg) on PN11-14, with assessments conducted on PN45, comparing each agent alone as well as sequential administration of both. Although neither treatment affected growth or viability, each elicited similar alterations in factors that are critical to the function of the <em>5HT</em> synapse: <em>5HT</em>1A receptors, <em>5HT</em>2 receptors, and the presynaptic <em>5HT</em> transporter (<em>5HT</em>T). Either agent elicited global increases in <em>5HT</em> receptors and the <em>5HT</em>T in brain regions possessing <em>5HT</em> cell bodies (midbrain, brainstem) as well as in the hippocampus, which contains <em>5HT</em> projections. For both terbutaline and CPF, males were affected more than females, although there were some regional disparities in the sex selectivity between the two agents. Both altered <em>5HT</em> receptor-mediated cell signaling, suppressing stimulatory effects on adenylyl cyclase and enhancing inhibitory effects. When animals were exposed sequentially to both agents, the outcomes were no more than additive and, for many effects, less than additive, suggesting convergence of the two agents on a common set of developmental mechanisms. Our results indicate that <em>5HT</em> systems represent a target for otherwise unrelated neuroteratogens.

Preliminary data on the existence of a plasma pool of serotonin (<em>5HT</em>) in human blood has been confirmed in a descriptive study of two distinctive pools of <em>5HT</em> (plasma and platelet), and its metabolite 5-hydroxyindoleacetic acid (5HIAA), in the blood of 175 healthy individuals. Plasma <em>5HT</em> (0.93 +/- 0.67 ng/mL, X +/- S.D.) shows a significant but low correlation with platelet <em>5HT</em> (711 +/- 319 ng/10(9) platelets) (r=0.29, p less than 0.001). Diastolic blood pressure correlated significantly with plasma <em>5HT</em> (r=0.51, p less than 0.05) and whole blood <em>5HT</em> (r=0.52, p less than 0.05) in older individuals (50-65 years) but not in the whole group (r=0.052, n.s.). Differences between sexes include plasma <em>5HT</em>, whole blood <em>5HT</em> (both higher in women) and plasma 5HIAA (lower in women) and may reflect a differential whole body <em>5HT</em> function. The effect of meal consumption and a peripheral <em>5HT</em> synthesis inhibitor (carbidopa) in four human subjects has also been tested. Carbidopa (0.7 mg/kg) significantly lowers the plasma pool of <em>5HT</em> (mean change -33%) 2 hr. after administration, while platelet <em>5HT</em> is unchanged. These data support the existence of a human plasma <em>5HT</em> pool, with a rapid turnover, different from the <em>5HT</em> in platelets (slow turnover, reserve pool). Both may be useful in evaluating different aspects of <em>5HT</em>-mediated pathologies.

The present study examined the effect of a low-dose of nicotine; below that one expects to be achieved from a single cigarette, on brain regional heterogeneity and sensitivity of catecholaminergic responses. 1 microM nicotine was infused into six brain areas via a microdialysis probe: the dorsal and ventral hippocampus, the medial temporal and prefrontal cortex, the basolateral amygdala, and the ventral tegmental area (VTA). The nicotine concentration in the brain tissue near the probe site was approximately 0.1 microM. Nicotine-induced increases and decreases could be noted in dopamine (DA), norepinephrine (NE), and serotonin (<em>5HT</em>) levels. In particular, DA and <em>5HT</em> decreased in both hippocampal areas, while NE increased in the dorsal and decreased in the ventral hippocampus. In the cortical areas, DA and NE increased and <em>5HT</em> was not significantly altered. In the amygdala all three neurotransmitters increased and in the VTA, all three decreased. Many of the nicotine-induced changes in neurotransmitter concentrations were reversed in the presence of atropine. Where nicotine induced decreases in DA and <em>5HT</em> in the VTA, increases were observed in the presence of atropine. A similar reversal was seen with NE in the VTA and ventral hippocampus. In contrast, the increases in DA observed in the cortex and amygdala and the increases in NE observed in the cortex, amygdala and dorsal hippocampus were inhibited by the presence of atropine. <em>5HT</em> was also significantly decreased in the amygdala and both cortical areas in the presence of atropine, where nicotine alone had no significant effect. We conclude, that at low doses, nicotine significantly alters the release of DA, NE, and <em>5HT</em>--in some areas increasing, in others decreasing endogenous neurotransmitter levels. This data, in conjunction with previous experiments, indicates that the effects of nicotine are regionally heterogeneous and arise from both direct and indirect actions on various receptors and neurotransmitter systems and nicotine's effects at low doses differ from that at higher doses. The changes in effects in the presence of atropine suggest that muscarinic acetylcholine receptors play a major role in nicotine's actions on neurotransmitter systems.

Growth-inhibitory chondroitin sulfate proteoglycans (CSPG) are a primary target for therapeutic strategies after spinal cord injury because of their contribution to the inhibitory nature of glial scar tissue, a major barrier to successful axonal regeneration. Chondroitinase ABC (ChABC) digestion of CSPGs promotes axonal regeneration beyond a lesion site with subsequent functional improvement. ChABC also has been shown to promote sprouting of spared fibers but it is not clear if functional recovery results from such plasticity. Here we sought to better understand the roles rostral or caudal sprouting may play in ChABC-mediated functional improvement. To achieve this, ChABC or vehicle was injected rostral or caudal to a unilateral C5 injury. When injected rostral to a hemisection, ChABC promoted significant sprouting of <em>5HT</em>+ fibers into dorsal and ventral horns. When ChABC was injected into tissue caudal to a hemisection, no additional sprouting was observed. When injected caudal to a hemicontusion injury, ChABC promoted sprouting of <em>5HT</em>+ fibers into the ventral horn but not the dorsal horn. None of this sprouting resulted in a change in the synaptic component synapsin, nor did it impact performance in behavioral tests assessing motor function. These data suggest that ChABC-mediated sprouting of spared fibers does not necessarily translate into functional recovery.

Arsenic is one of the most common heavy metal contaminants found in the environment, particularly in water. We examined the impact of perinatal exposure to relatively low levels of arsenic (50 parts per billion, ppb) on neuroendocrine markers associated with depression and depressive-like behaviors in affected adult C57BL/6J mouse offspring. Whereas most biomedical research on arsenic has focused on its carcinogenic potential, a few studies suggest that arsenic can adversely affect brain development and neural function. Compared to controls, offspring exposed to 50 parts per billion arsenic during the perinatal period had significantly elevated serum corticosterone levels, reduced whole hippocampal CRFR 1 protein level and elevated dorsal hippocampal serotonin <em>5HT</em> 1A receptor binding and receptor-effector coupling. <em>5HT</em> 1A receptor binding and receptor-effector coupling were not different in the ventral hippocampal formation, entorhinal or parietal cortices, or inferior colliculus. Perinatal arsenic exposure also significantly increased learned helplessness and measures of immobility in a forced swim task. Taken together, these results suggest that perinatal arsenic exposure may disrupt the regulatory interactions between the hypothalamic-pituitary-adrenal axis and the serotonergic system in the dorsal hippocampal formation in a manner that predisposes affected offspring to depressive-like behavior. These results are the first to demonstrate that relatively low levels of arsenic exposure during development can have long-lasting adverse effects on behavior and neurobiological markers associated with these behavioral changes.

Central chemoreception is a distributed property involving many sites and neuronal types. Focal acidosis in conscious or anesthetized animals at many hindbrain sites stimulates breathing. The steady-state CO2 response in conscious animals is reduced by cell specific lesions of catecholamine, <em>5HT</em> or neurokinin-1 receptor (NK1R) expressing neurons and by focal inhibition at the retrotrapezoid nucleus (RTN) and medullary raphe (MR). Is the steady-state CO2 response a physiologically relevant way to study central chemoreception? Central chemoreceptors also: (1) provide a 'tonic drive' to breathe, (2) are modified by and/or modulate other control systems, e.g., temperature and hypoxia, (3) affect breath-to-breath variability, (4) can respond dynamically to few breath changes in CO2, and (5) interact in complex ways. We contend that central chemoreceptors detect interstitial pH and thus monitor the balance of arterial PCO2, cerebral blood flow and neuronal/glial metabolism. They affect physiological control systems in many ways, perhaps not all measurable, via the study of the steady-state CO2 response.

Methamphetamine (METH) is a neurotoxic drug of abuse that damages the dopamine (DA) neuronal system in a highly delimited manner. The brain structure most affected by METH is the striatum where long-term DA depletion and microglial activation are maximal. Endogenous DA has been implicated as a critical participant in METH-induced neurotoxicity, most likely as a substrate for non-enzymatic oxidation by METH-generated reactive oxygen species. The striatum is also extensively innervated by serotonin (<em>5HT</em>) nerve endings and this neurochemical system is modified by METH in much the same manner as seen in DA nerve endings (i.e., increased release of <em>5HT</em>, loss of function in tryptophan hydroxylase and the serotonin transporter, long-term depletion of <em>5HT</em> stores). <em>5HT</em> can also be modified by reactive oxygen species to form highly reactive species that damage neurons but its role in METH neurotoxicity has not been assessed. Increases in <em>5HT</em> levels with 5-hydroxytryptophan do not change METH-induced neurotoxicity to the DA nerve endings as revealed by reductions in DA, tyrosine hydroxylase and dopamine transporter levels. Partial reductions in <em>5HT</em> with p-chlorophenylalanine are without effect on METH toxicity, despite the fact that p-chlorophenylalanine largely prevents METH-induced hyperthermia. Mice lacking the gene for brain tryptophan hydroxylase 2 are devoid of brain <em>5HT</em> and respond to METH in the same manner as wild-type controls, despite showing enhanced drug-induced hyperthermia. Taken together, the present results indicate that endogenous <em>5HT</em> does not appear to play a role in METH-induced damage to DA nerve endings of the striatum.

Voluntary exercise has been associated with reduced anxiety across several animal models. Manipulation of central 5-HT can alter anxiety-like behaviors and administration of the 5-HT agonist metachlorophenylpiperazine (mCPP) increases anxiety in rodents and humans. To examine whether the anxiolytic effect of exercise is associated with an alteration in 5-HT systems, we examined the anxiogenic effect of mCPP in exercising and nonexercising mice. C57BL/6J mice were given 2 weeks of free access to either a functioning or nonfunctioning running wheel. Mice were then tested for acoustic startle following systemic injection of either 0, 0.1, 0.3, or 1 mg/kg of mCPP. Consistent with its anxiogenic properties, mCPP produced a dose-dependent increase in acoustic startle in nonexercising mice. However, this anxiogenic effect was blunted in exercising mice. These findings suggest that exercise may help to reduce anxiety by altering 5-HT systems, perhaps by down-regulating postsynaptic <em>5HT</em> 2B/2C receptors.

The murine F9-derived 1C11 clone exhibits a stable epithelial morphology, expresses nestin, an early neuroectodermal marker, and expresses genes involved in neuroectodermal cell fate. Upon appropriate induction, 100% of 1C11 precursor cells develop neurite extensions and acquire neuronal markers (N-CAM, synaptophysin, gammagamma-enolase, and neurofilament) as well as the general functions of either serotonergic (1C11*(/<em>5HT</em>)) (<em>5HT</em>, 5-hydroxytryptamine) or noradrenergic (1C11**(/NE)) (NE, norepinephrine) neurons. The two programs are shown to be mutually exclusive. 1C11 thus behaves as a neuroepithelial cell line with a dual bioaminergic fate. 1C11*(/<em>5HT</em>) cells implement a functional 5-HT transporter and thereby a complete serotonergic phenotype within 4 days, whereas 5-HT(1B/D), 5-HT(2B), and 5-HT(2A) receptors are sequentially induced. The accurate time schedule of catecholaminergic differentiation was defined. Catecholamine synthesis, storage, and catabolism are acquired within 4 days; the noradrenergic phenotype is complete at day 12 and includes a functional norepinephrine transporter and an alpha(1D)-adrenoreceptor (day 8). The time-dependent onset of neurotransmitter-associated functions proper to either program is similar to in vivo observations. Along each pathway, the selective induction of serotonergic or adrenergic receptors is shown to be an essential part of the differentiation program, since they promote an autoregulation of the corresponding phenotype.

In transfected cells and non-neuronal tissues many G-protein-coupled receptors activate p44/42 MAP kinase (ERK), a kinase involved in both hippocampal synaptic plasticity and learning and memory. However, it is not clear to what degree these receptors couple to ERK in brain. G(s)-coupled beta-adrenergic receptor activation of ERK in neurons is critical in the regulation of synaptic plasticity in area CA1 of the hippocampus. In addition, alpha(1)- and alpha(2)-adrenergic receptors, present in CA1, could potentially activate ERK. We find that, like the beta-adrenergic receptor, the G(q)-coupled alpha(1)AR activates ERK in adult mouse CA1. However, activation of the G(i/o)-coupled alpha(2)AR does not activate ERK, nor does activation of a homologous G(i/o)-coupled receptor enriched in adult mouse CA1, the <em>5HT</em>(1A) receptor. In contrast, the nonhomologous G(i/o)-coupled gamma-aminobutyric acid type B receptor does activate ERK in adult mouse CA1. Surprisingly, activation of alpha(2)ARs in CA1 from immature animals where basal phospho-ERK is low induces ERK phosphorylation. These data suggest that although most G-protein-coupled receptor subtypes activate ERK in non-neuronal cells, the coupling of G(i/o) to ERK is tightly regulated in brain.

The exposure to bright light of dark-adapted (DKA) mouse retinas incubated in the dark (DI) in IBMX-containing medium causes a marked loss of cyclic AMP. This light response also occurs if the medium contains 10 mM aspartate or cobaltous ion, agents believed to confine the effects of light to photoreceptors. Thus, the action of light in the presence of either of these agents defines a light-sensitive pool of cyclic AMP in photoreceptors. This pool could also be reduced or eliminated in DKA-DI retinas by nanomolar to micromolar levels of dopamine (if the medium contained SCH23390, a potent antagonist of D1 receptors), thus indicating an agonistic action of dopamine at D2 receptors. The D2 agonists LY171555 (EC50 10 nM) or (+)-3-PPP also reduced the cyclic AMP level in the dark. Of the D2 antagonists tested, the butyrophenone spiperone (in the presence of the <em>5HT</em>-2 blocker ketanserin) countered the action of the D2 agonists but substituted benzamides were ineffective. Consistently, the D2 agonists had no effect on cyclic AMP levels of mutant retinas lacking photoreceptors (rd/rd), but reduced cyclic AMP in DKA-DI glutamate-modified retinas which exhibit a major loss of inner retinal neurons without apparent loss of photoreceptors. The D1 antagonist SCH23390 only reduced cyclic AMP levels of DKA-DI retinas when cyclic AMP levels had been elevated by adding dopamine to the incubation medium.

Abnormalities in serotonin receptor subtypes have been observed in the postmortem brain of suicide victims. We examined the regional distribution of serotonin (<em>5HT</em>)(2C) receptor mRNA in several areas of the human brain and also compared its protein and mRNA expression in the prefrontal cortex (PFC), hippocampus, and choroid plexus between suicide victims and normal control subjects. <em>5HT</em>(2C) receptors were found to be distributed in several areas of the human brain (in order of abundance): highly concentrated and richest in choroid plexus; hypothalamus; nucleus accumbens; with the lowest abundance in PFC and cerebellum. Comparison of <em>5HT</em>(2C) receptors between suicide victims and control subjects showed higher protein levels in the PFC but not the hippocampus or choroid plexus of suicide victims. However, there were no significant differences in mRNA levels between suicide victims and control subjects in these brain areas. These results suggest that <em>5HT</em>(2C) receptors are richly distributed throughout the brain with the highest level in the choroid plexus and that abnormalities in protein expression of <em>5HT</em>(2C) receptors in the PFC may be associated with suicide.

Lithium is an effective drug for both treatment and prophylaxis of bipolar disorder. However, the mechanism of lithium action is still unknown. The inositol depletion hypothesis is supported by biochemical and behavioral data in rats, but primate inositol levels are higher than in rodents and may obviate the effects of depletion. Inhibition of <em>5HT</em> autoreceptors by lithium is supported by biochemical and behavioral data in rats but would seem more related to lithium's antidepressant than to its antimanic or prophylactic effects. Lithium induces increases in levels of the anti-apoptotic factor Bcl-2. This effect could be most relevant for treatment of neurodegenerative disorders. Lithium inhibits glycogen synthase kinase-3, which is involved in a wide range of signal transduction pathways. However, this lithium effect occurs at high concentrations and may be more relevant for its toxic effect. Lithium in low concentrations induces accumulation of PAP, which affects several cellular processes including RNA processing. However, PAP phosphatase is present more in peripheral tissues than in brain. This lithium effect could explain some of its peripheral side effects. Chronic lithium administration upregulates glutamate reuptake and thus decreases glutamate availability in synapse. Glutamate is an excitatory neurotransmitter and its reduction could exert an antimanic effect. Biochemical and clinical experiments are necessary to determine the key mechanism of lithium efficacy in treatment and prophylaxis of affective disorders.

Impaired <em>5HT</em> functioning has been implicated in two very different psychiatric syndromes: antisocial personality disorder and depression. In both, reduced csf concentration of 5HIAA and blunted circulating hormone responses to <em>5HT</em> drug challenge have been described. The paradox can be resolved by the theory that the two main ascending <em>5HT</em> pathways mediate adaptive responses to future and current adversity. Projections of the anterior group of raphe <em>5HT</em> cells (dorsal raphe nucleus) oppose the action of dopamine and mediate avoidance of threats. Impaired function sensitises the dopamine system resulting in impulsivity and drug addiction. Posterior <em>5HT</em> cells (median raphe nucleus) innervate hippocampus and cingulate gyrus and suppress memory and awareness of current and past adversity. Impaired function results in low mood, low self-esteem, hopelessness and pessimism. Modern imaging methods are providing startling corroboration of these ideas.

Urotensin II is a cyclic undecapeptide which activates the GPR14 receptor and exerts potent vasoconstrictor effects in some species of fish and mammals. The present study intended to investigate isolated vessels from various species in an attempt to find sensitive preparations to be used in studies of the human urotensin (hU-II)/GPR14 system. Contractile responses evoked by noradrenaline (NA), angiotensin II (Ang II), endothelin 1 (ET-1) and hU-II were measured in large vessels (aorta and some large arteries and veins) of rats, guinea pigs, rabbits, pigs and humans. Relaxing effects of hU-II, bradykinin (BK) and substance P (SP) were measured in pig coronary arteries contracted with KCl 30 mM. The rat mesenteric vasculature was investigated from the arterial and venous site to establish the function of ET-1 and hU-II receptors. Results indicate that the only preparation showing high sensitivity to hU-II (pEC(50)=8.27) is the rat aorta, whose contractions in response to hU-II develop slowly and persist for hours, similar to those of ET-1 (pEC(50)=8.35). Effects of NA (pEC(50)=8.12) and Ang II (pEC(50)=7.95) develop and reverse more rapidly. Tissues treated with ET-1 and hU-II show marked desensitization, in contrast to those treated with NA. Specific antagonists for alpha(1) (prazosin, p A(2)=10.46), AT(1) (EXP 3174, p A(2)=10.20), <em>5HT</em>(2) (ketanserine, p A(2)=8.61) and ET(A)-ET(B) (bosentan, p A(2)=6.88) receptors were shown to block the effects of the respective agonists, while being inactive against hU-II. In some vessels, hU-II behaved as an highly potent but scarcely effective contractile agent. It is concluded that: the hU-II/GPR14 is not a functional contractile system in vessels of several species, in contrast with NA/alpha(1), Ang II/AT(1), <em>5HT</em>/<em>5HT</em>(2) and ET-1/ET(A)-ET(B). The rat aorta appears however to be a sensitive and reliable preparation for evaluating biological activities of hU-II and related peptides.

The effects of manipulating 5-hydroxytryptamine (<em>5HT</em>) neuronal function in humans and in animals are reviewed. <em>5HT</em> pathways do not have a unitary function in modulating anxiety. It is proposed that, rather than acting as input or output channels for brain aversive systems, these pathways provide information concerning waking/motor status, which is crucial to the organisation of appropriate responses to threat. Each terminal region can make use of this information in different ways. Globally, the influence of <em>5HT</em> neurones on higher centres appears predominantly to facilitate information processing relevant to threat, while their major influence on brainstem centres may be a restraining one.