Simultaneous detection of indoleamines and dopamine in rat dorsal raphe nuclei using specific antibodies

Optogenetic activation of DRN 5-HT neurons induced active wakefulness, not quiet wakefulness

There has been a long-standing controversy regarding the physiological role of serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) in sleep/wake architecture. Some studies have reported that 5-HT acts as a sleep-promoting agent, but several studies have suggested that DRN 5-HT neurons function predominantly to promote wakefulness and inhibit rapid eye movement (REM) sleep. Furthermore, recent studies have reported that there is a clear neurobiological difference between a waking state that includes alertness and active exploration (i.e., active wakefulness) and a waking state that is devoid of locomotion (i.e., quiet wakefulness). These states have also been shown to differ clinically in terms of memory consolidation. However, the effects of 5-HT neurons on the regulation of these two different waking states have not been fully elucidated. In the present study, we attempted to examine the physiological role of DRN 5-HT neurons in various sleep/wake states using optogenetic methods that allowed manipulation of cell-type specific neuronal activation with high temporal and anatomical precision. We crossed TPH2-tTA and TetO-ChR2(C128S) mice to obtain mice with channelrhodopsin-2 (ChR2) [C128S]-expressing central 5-HT neurons, and we activated DRN-5HT neurons or medullary 5-HT neurons. Optogenetic activation of DRN 5-HT neurons caused rapid transition from non-REM sleep to active wakefulness, not quiet wakefulness, whereas activation of medullary 5-HT neurons did not appear to affect sleep/wake states or locomotor activity. Our results may shed light on the physiological role of DRN 5-HT neurons in sleep/wake architecture and encourage further investigations of the cortical functional connectivity involved in sleep/wake state regulation.

Functional Connectivity of the Raphe Nuclei: Link to Tobacco Withdrawal in Smokers

BACKGROUND

Although nicotine alters serotonergic neurochemistry, clinical trials of serotonergic medications for smoking cessation have provided mixed results. Understanding the role of serotonergic dysfunction in tobacco use disorder may advance development of novel pharmacotherapies.

METHODS

Functional magnetic resonance imaging was used to measure resting-state functional connectivity of the raphe nuclei as an indicator of serotonergic function. Connectivity of the dorsal and median raphe nuclei was compared between 18 young smokers (briefly abstinent, ~40 minutes post-smoking) and 19 young nonsmokers (16-21 years old); connectivity was also examined in a separate sample of overnight-abstinent smokers (18-25 years old), before and after smoking the first cigarette of the day. Relationships between connectivity of the raphe nuclei with psychological withdrawal and craving were tested in smokers.

RESULTS

Connectivity of the median raphe nucleus with the right hippocampal complex was weaker in smokers than in nonsmokers and was negatively correlated with psychological withdrawal in smokers. In overnight-abstinent smokers, smoking increased connectivity of the median raphe nucleus with the right hippocampal complex, and the increase was positively correlated with the decrease in psychological withdrawal.

CONCLUSIONS

Relief of withdrawal due to smoking is potentially linked to the serotonergic pathway that includes the median raphe nucleus and hippocampal complex. These results suggest that serotonergic medications may be especially beneficial for smokers who endorse strong psychological withdrawal during abstinence from smoking.

The effects of local microinjection of selective dopamine D1 and D2 receptor agonists and antagonists into the dorsal raphe nucleus on sleep and wakefulness in the rat

The effects of the dopamine (DA) D1 and D2 receptor agonists SKF38393, bromocriptine and quinpirole, respectively, on spontaneous sleep were analyzed in adult rats prepared for chronic sleep recordings. Local administration of the DAergic agonists into the dorsal raphe nucleus (DRN) during the light phase of the light-dark cycle induced a significant reduction of rapid-eye movement sleep (REMS) and the number of REM periods. Additionally, bromocriptine and quinpirole significantly increased wakefulness (W). Opposite, the microinjection into the DRN of the DA D1 and D2 receptor antagonists SCH23390 and sulpiride, respectively, significantly augmented REMS and the number of REM periods. Pretreatment with SCH23390 and sulpiride prevented the effects of SKF38393 and bromocriptine, respectively, on sleep variables. Our results tend to indicate that DAergic neurons located in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) contribute to the regulation of predominantly W and REMS by DRN serotonergic neurons.

The mysterious trace amines: protean neuromodulators of synaptic transmission in mammalian brain

The trace amines are a structurally related group of amines and their isomers synthesized in mammalian brain and peripheral nervous tissues. They are closely associated metabolically with the dopamine, noradrenaline and serotonin neurotransmitter systems in mammalian brain. Like dopamine, noradrenaline and serotonin the trace amines have been implicated in a vast array of human disorders of affect and cognition. The trace amines are unique as they are present in trace concentrations, exhibit high rates of metabolism and are distributed heterogeneously in mammalian brain. While some are synthesized in their parent amine neurotransmitter systems, there is also evidence to suggest other trace amines may comprise their own independent neurotransmitter systems. A substantial body of evidence suggests that the trace amines may play very significant roles in the coordination of biogenic amine-based synaptic physiology. At high concentrations, they have well-characterized presynaptic "amphetamine-like" effects on catecholamine and indolamine release, reuptake and biosynthesis; at lower concentrations, they possess postsynaptic modulatory effects that potentiate the activity of other neurotransmitters, particularly dopamine and serotonin. The trace amines also possess electrophysiological effects that are in opposition to these neurotransmitters, indicating to some researchers the existence of receptors specific for the trace amines. While binding sites or receptors for a few of the trace amines have been advanced, the absence of cloned receptor protein has impeded significant development of their detailed mechanistic roles in the coordination of catecholamine and indolamine synaptic physiology. The recent discovery and characterization of a family of mammalian G protein-coupled receptors responsive to trace amines such as beta-phenylethylamine, tyramine, and octopamine, including socially ingested psychotropic drugs such as amphetamine, 3,4-methylenedioxymethamphetamine, N,N-dimethyltryptamine, and lysergic acid diethylamide, have revitalized the field of scientific studies investigating trace amine synaptic physiology, and its association with major human disorders of affect and cognition.

Effects of 5,7-dihydroxytryptamine lesion of the dorsal raphe nucleus on ethanol discrimination in the rat

It has been shown that ethanol produces a complex interoceptive cue in rodents with distinct GABAergic, glutamatergic, and serotonergic (5-hydroxytryptamine, 5-HT) components. The present study aimed to examine the contribution of the 5-HT system originating in the dorsal raphe nucleus (DRN) to the discriminative stimulus effects of ethanol in male Wistar rats. Therefore, selective lesions of 5-HT neurons in the DRN were induced by microinfusions of 5,7-dihydroxytryptamine. The DRN- and sham-lesioned rats were trained to discriminate ethanol (1.0 g/kg) from saline in a standard two-lever drug discrimination procedure. Acquisition of ethanol discrimination and discrimination performance after consumption of lower doses of ethanol did not differ between the groups. In substitution tests, diazepam (0.5-2.5 mg/kg), a nonselective benzodiazepine receptor agonist, partially generalized from the ethanol cue in both groups. In contrast, m-chlorophenylpiperazine (0.1-0.9 mg/kg), a mixed 5-HT(1B/2C) receptor agonist, did not mimic the ethanol cue. The drug decreased response rates in both groups, but this effect was more evident in the sham-lesioned group. A 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propyloamino)-tetraline (0.05-0.4 mg/kg), did not produce significant increase in ethanol-appropriate responding in either group. These results may indicate that 5-HT neurons of the DRN are not critically involved in ethanol discrimination in the rat.

Control of serotonergic neurons in rat brain by dopaminergic receptors outside the dorsal raphe nucleus

We studied the control of dorsal raphe (DR) serotonergic neurons by dopaminergic transmission in rat brain using microdialysis and single unit extracellular recordings. Apomorphine (0.5-3.0 mg/kg s.c.) and quinpirole (0.5 mg/kg s.c.) increased serotonin (5-HT) output in the DR and (only apomorphine) in striatum. These effects were antagonized by 0.3 mg/kg s.c. SCH 23390 (in DR and striatum) and 1 mg/kg s.c. raclopride (in DR). 5-HT(1A) receptor blockade potentiated the 5-HT increase produced by apomorphine in the DR. Apomorphine (50-400 microg/kg i.v.) increased the firing rate of most 5-HT neurons, an effect prevented by SCH 23390 and raclopride. Quinpirole (40-160 microg/kg i.v.) also enhanced the firing rate of 5-HT neurons. When applied in the DR, neither drug increased the 5-HT output in the DR or striatum. Likewise, micropressure injection of quinpirole (0.2-8 pmol) failed to increase the firing rate of 5-HT neurons. In situ hybridization showed that the dopamine (DA) D(2) receptor transcript was almost absent in the DR and abundant in the substantia nigra (SN) and the periaqueductal grey matter (PAG). Using dual probe microdialysis, the application of tetrodotoxin or apomorphine in SN significantly increased the DR 5-HT output. Thus, the discrepancy between local and systemic effects of dopaminergic agonists and the absence of DA D(2) receptor transcript in 5-HT neurons suggest that DA D(2) receptors outside the DR control serotonergic activity.

Dopaminergic input is required for increases in serotonin output produced by behavioral activation: an in vivo microdialysis study in rat forebrain

Previous research has demonstrated that pharmacological stimulation of postsynaptic dopamine D2 receptors produces increases in serotonin output. The present study explored whether this relationship also holds under physiological conditions. Accordingly, we examined the effects of D2 receptor blockade or unilateral dopamine depletion on behaviorally induced increases in extracellular serotonin levels in the corpus striatum and prefrontal cortex of freely moving rats using in vivo microdialysis. Extracellular levels of dopamine and serotonin, as well as behavioral activity, were increased by both mild tail pinch and the light-dark transition. Tail pinch-induced increases in serotonin levels (39+/-3% and 53+/-5% in the corpus striatum and prefrontal cortex, respectively), but not the accompanying behavioral changes, were blocked by local application of the D2 receptor antagonist raclopride (10 microM). D2 receptor blockade also disrupted the positive relationship between striatal serotonin levels and behavioral activity of animals across the light-dark transition (r=0.93 without raclopride, r=0.24 in presence of raclopride). Unilateral 6-hydroxydopamine lesion of the nigrostriatal dopaminergic system also abolished increases in striatal serotonin output induced by both tail pinch and light-dark transition. A negative correlation was observed between the degree of striatal dopamine depletion and tail pinch-induced increases in serotonin efflux (r= - 0.88). Thus, both a local blockade of postsynaptic D2 receptors and striatal dopamine depletion prevented increases in serotonin output that normally accompany behavioral activation. These data indicate that the increases in the forebrain serotonin output produced by two distinct physiological/environmental manipulations appear to be largely dependent upon intact local dopaminergic neurotransmission.

Tryptamine, serotonin and catecholamines: an immunocytochemical study in the central nervous system

Tryptamine, a serotonin-related indolamine, could be involved in the modulation of catecholaminergic and serotoninergic systems interaction. Despite previous reports on this topic, the morphological relationship among these systems is not well described. We studied the interaction among serotoninergic and catecholaminergic with tryptaminergic systems by double immunostaining at the level of light microscopy. Mesencephalic rat brain sections treated according to the Schiff quenching method were double immunostained using peroxidase and fluorescein labeled antibodies. Primary antibodies to anti-tryptophan hydroxylase (TrpOH), anit-tyrosine hydroxylase (TH) and anti-tryptamine (T) were used to demonstrate serotoninergic, catecholaminergic and tryptaminergic neurons respectively. A morphometric study was performed in order to analyze the different morphological characteristics of each system. The results showed that (i) T+ and TrpOH+ neurons are localized in the same areas but their morphology is significantly different. Moreover morphometric parameters of T+ neurons were significantly different from those TrpOH+ or TH+ neurons; (ii) The number of TrpOH+ neurons was larger than T+ neurons; (iii) T+ neurons were dominant in the lateral dorsal raphe nucleus. TrpOH+ neurons were more numerous in the central area of the dorsal raphe nucleus; (iv) Coexpression of TrpOH and T was demonstrated in the somata of dorsal raphe nucleus neurons; (v) TrpOH+ neurons from raphe nuclei and TH+ neurons from substantia nigra are contacted by T+ fibres. The present morphological evidence supports a functional relationship among these three aminergic systems.

Involvement of dopamine D2 receptors in apomorphine-induced facilitation of forebrain serotonin output

The effect of systemic administration of the nonselective dopamine receptor agonist apomorphine on efflux of serotonin (5-hydroxytryptamine, 5-HT) in striatum and hippocampus of freely moving rats was examined using in vivo microdialysis. 5-HT efflux was increased by a moderate dose of apomorphine sufficient for a postsynaptic dopaminergic effect (0.5 mg/kg, s.c.), but not by a lower dose (0.1 mg/kg, s.c.), that acts preferentially on presynaptic dopamine receptors. This effect was blocked by a dopamine D2 receptor antagonist raclopride, administered either systemically or locally into striatum, but not by a 5-HT1A receptor antagonist N-¿2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl¿-N-(2-pyridinyl) cyclohexanecarboxamide 3HCI (WAY-100635). This indicates that dopamine D2 receptors, and not 5-HT1A receptors, mediate the facilitatory effect of apomorphine, and that this effect occurs at the nerve terminal level. Behavioral effects of apomorphine outlasted the concomitant changes in 5-HT efflux, suggesting that these changes resulted from dopaminergic receptor activation, rather than from the drug-induced behavioral arousal.

Serotonergic dorsal raphe nucleus projections to the cholinergic and noncholinergic neurons of the pedunculopontine tegmental region: a light and electron microscopic anterograde tracing and immunohistochemical study

The serotonergic dorsal raphe nucleus is considered an important modulator of state-dependent neural activity via projections to cholinergic neurons of the pedunculopontine tegmental nucleus (PPT). Light and electron microscopic analysis of anterogradely transported biotinylated dextran, combined with choline acetyltransferase (ChAT) immunohistochemistry, were employed to describe the synaptic organization of mesopontine projections from the dorsal raphe to the PPT. In a separate set of experiments, we utilized immunohistochemistry for the serotonin transporter (SERT), combined with ChAT immunohistochemistry at the light and electron microscopic levels, to determine whether PPT neurons receive serotonergic innervation. The results of these studies indicate that: (1) anterogradely labeled and SERT-immunoreactive axons and presumptive boutons invest the PPT at the light microscopic level; (2) at the ultrastructural level, dorsal raphe terminals in the PPT pars compacta synapse mainly with dendrites and axosomatic contacts were not observed; (3) approximately 12% of dorsal raphe terminals synapse with ChAT-immunoreactive dendrites; and (4) at least 2-4% of the total synaptic input to ChAT-immunoreactive dendrites is of dorsal raphe and/or serotonergic origin. This serotonergic dorsal raphe innervation may modulate cholinergic PPT neurons during alterations in behavioral state. The role of these projections in the initiation of rapid eye movement (REM) sleep and the ponto-geniculo-occipital waves that precede and accompany REM sleep is discussed.

Selective destruction of midbrain raphe nuclei by 5,7-DHT: is brain 5-HT involved in alcohol drinking in Sprague-Dawley rats?

Since serotonin (5-HT) reportedly is involved in aberrant drinking of ethyl alcohol, the present study examined a possible role of the concentration of 5-HT in systems originating in the dorsal raphe nucleus (DRN), median raphe nucleus (MRN) or both nuclei. The preference for alcohol offered in concentrations increased over 10 days from 3% to 30% was determined for each Sprague-Dawley rat. After the rats were anesthetized with sodium pentobarbital, either 10 microg 5,7-DHT or artificial cerebrospinal fluid (CSF) was micro-injected stereotaxically into the DRN, MRN or both nuclei. After 10 days, a second alcohol preference test was offered to the animals. Then the rats were decapitated, each brain removed, and the block of tissue containing injection sites was saved for histological analysis. The remaining portion was dissected into separate regions for analysis by HPLC of 5-HT, 5-hydroxyindoleacetic-acid (5-HIAA), norepinephrine (NE), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). The 5,7-DHT lesion of the DRN depleted the levels of 5-HT and 5-HIAA by 50-55% in the midbrain and pons and by 70-80% in the frontal cortex, whereas, the 5,7-DHT lesion of MRN reduced 5-HT in all regions except the corpus striatum. The depletion of 5-HT was lower in MRN-lesioned than in DRN-lesioned rats in the frontal cortex and nucleus accumbens. The combined lesion of both DRN and MRN produced a massive decline of >90% of 5-HT and 5-HIAA in all structures except the pons where 5-HT was reduced by 70%. Whereas the level of NE was reduced mainly in the frontal cortex, the levels of DA and its metabolites were essentially unaffected by the 5,7-DHT lesions. Although single or combined lesions of the DRN and MRN failed to alter the intake of alcohol of the rats, the combined serotonergic lesions increased significantly the ingestion of water but not food. Correlational analyses in the sham groups showed a negative association between the intake of alcohol and cortical dopamine and possible hippocampal 5-HT and NE as well as between the ingestion of food and of 5-HT in the frontal cortex. Taken together, these observations in the Sprague-Dawley rat suggest that lower levels of these monoamines in certain regions of the brain may play a role in the maintenance of the basal intake of alcohol but not in the drinking after the injection of 5,7-DHT. Explanations of our findings include: (1) a compensatory neurochemical change in pre- or postsynaptic 5-HT receptors subsequent to the dysfunction of serotonergic neurons in the forebrain; (2) a unique characteristic of the Sprague-Dawley strain of rat; and (3) residual quanta of 5-HT which sustains the pattern of alcohol drinking.

Exogenous L-5-hydroxytryptophan is decarboxylated in neurons of the substantia nigra pars compacta and locus coeruleus of the rat

The aim of the present study is to examine by immunohistochemistry whether exogenous L-5-hydroxytryptophan (L-5HTP) is decarboxylated in neurons of the substantia nigra pars compacta (SNC) and locus coeruleus (LC) of the rat. In normal rats, neurons of the SNC and LC stained intensely for aromatic L-amino acid decarboxylase (AADC). No serotonin (5HT)-positive cells were found in the two regions of the normal rats. In rats that were intraperitoneally injected with L-5HTP alone, the SNC neurons stained deeply for 5HT, but the LC neurons showed only a faint staining for 5HT. In rats that intraperitoneally received both a monoamine oxidase (MAO) inhibitor and L-5HTP, when compared with the L-5HTP-injected rats, the LC neurons became much darker in 5HT staining, but the SNC neurons showed only a slight increase in 5HT staining. The present findings suggest that (i) AADC in dopaminergic neurons of the SNC and in noradrenergic neurons of the LC can catalyze the in vivo decarboxylation of exogenous L-5HTP to produce 5HT, and (ii) most of the newly produced 5HT in the LC neurons is rapidly degraded by endogenous MAO.

Immunohistochemical evidence that central serotonin neurons produce dopamine from exogenous L-DOPA in the rat, with reference to the involvement of aromatic L-amino acid decarboxylase

The aim of the present study is to examine whether aromatic L-amino acid decarboxylase (AADC) catalyzes the conversion of exogenous L-3,4-dihydroxyphenylalanine (L-DOPA) to dopamine in serotonin neurons of the rat dorsal raphe nucleus. First, in order to confirm the localization of AADC in central serotonin neurons, we used an immunoperoxidase method for AADC and demonstrated that the distribution of AADC-containing neurons in the dorsal raphe nucleus corresponds very closely to the previous description on the distribution of serotonin-immunoreactive neurons. Second, in the rat that received intraperitoneally L-DOPA plus a peripheral AADC inhibitor, we used a double-labeling immunofluorescence method and showed that serotonin-stained neurons of the dorsal raphe nucleus were also immunoreactive to dopamine. The present result suggests that AADC decarboxylating L-5-hydroxytryptophan to serotonin in physiological conditions is also able to catalyze the in vivo decarboxylation of exogenous L-DOPA.

Dopamine D2 receptor-mediated regulation of serotonin extracellular concentration in the dorsal raphe nucleus of freely moving rats

Morphological and pharmacological data suggest the existence of a reciprocal interaction between the mesencephalic dopamine (DA) system and the serotonin (5-HT) system originating in the dorsal raphe nucleus (DRN). In the present work, a DA D2 receptor-mediated regulation of 5-HT extracellular concentrations in the DRN is described, by using brain microdialysis in freely moving rats. Local infusion of the nonselective DA agonist apomorphine produced a dose-dependent increase in the extracellular concentration of 5-HT in the DRN, which was prevented by previous infusion of the specific D2 antagonist raclopride but not of the D1 antagonist SCH-23390. Furthermore, local infusion of the selective D2 agonist LY-171,555 increased extracellular 5-HT levels in the DRN, and this effect was also prevented by the previous infusion of raclopride. It is postulated that DA, either from projections from the substantia nigra or the ventral tegmental area or from the DA-containing neurons of the DRN, may increase 5-HT release in the DRN, which, through autoreceptor stimulation, can profoundly influence the activity of ascending serotoninergic neurons.

Identification of tryptamine and tryptamine-serotonin neurons in the rat dorsal raphe nuclei using specific antibodies

Previous studies have shown that tryptamine (T) is closely associated with the serotonergic system but have failed to determine whether neurons containing only T exist in the raphe nuclei (RN) and/or if T colocalizes with serotonin (5-HT). The use of rabbit-conjugated T antisera (TAS) and rat-conjugated 5-HT antisera (5-HTAS) in a double-labelling technique has made the study of the colocalization of T and 5-HT in neurons of the rat dorsal RN (DR) possible. Slices taken from the same zone of the DR were treated following four different procedures of double-immunolabelling: DAB coloration for the rabbit TAS and DAB-nickel coloration for the rat 5-HTAS either first or second; or DAB coloration for the 5-HTAS and DAB-nickel coloration for the TAS first or second. Control sections were treated according to a single immunoperoxidase staining in the same zone. The immunolabelled neurons were computed using the Biocom 200 program at the same magnification. The results of this double-immunolabelling show that three different cell types exist in the rat DR: (1) T-only-containing neurons, (2) 5-HT-only-containing neurons displaying either homogeneous DAB or homogeneous DAB-nickel, and (3) neurons where T colocalizes with 5-HT (T-positive/5-HT-positive neurons) displaying heterogeneous DAB-nickel coloration. The results were identical whatever the procedure performed or the order of the DAB-nickel revelation.(ABSTRACT TRUNCATED AT 250 WORDS)

Tryptamine: a metabolite of tryptophan implicated in various neuropsychiatric disorders

Although early interest in the biomedical relevance of tryptamine has waned in recent years, it is clear from the above discussion that the study of tryptamine is worthy of serious consideration as a factor in neuropsychiatric disorders. The study of [3H]-tryptamine binding sites indicates an adaptive responsiveness characteristic of functional receptors. The question raised by Jones (1982d) on whether tryptamine is acting centrally as a neurotransmitter or a neuromodulator still remains mostly unanswered, although the evidence cited within this review strongly suggests a modulatory role for this neuroactive amine (see also Juorio and Paterson, 1990). The synthesis and degradative pathways of tryptamine, as well as the intricate neurochemical and behavioral consequences of altering these pathways, are now more fully understood. It is not yet clear what the role of tryptamine is under normal physiological [homeostatic] conditions, however, its role during pathological conditions such as mental and physical stress, hepatic dysfunction and other disorders of metabolism (i.e. electrolyte imbalance, increased precursor availability, enzyme induction or alterations in enzyme co-factor availability) may be quite subtle, perhaps accounting for various sequelae hitherto considered idiopathic. The evidence for a primary role for tryptamine in the etiology of mental or neurological diseases is still relatively poor, although the observations that endogenous concentrations of tryptamine are particularly susceptible to pharmacological as well as physiological manipulations serve to reinforce the proposition that this indoleamine is not simply a metabolic accident but rather a neuroactive compound in its own right. Finally, one might wonder what proportion of the data attributed to modifications of 5-HT metabolism might, in fact, involve unrecognized changes in the concentrations of other neuroactive metabolites of tryptophan such as tryptamine.

First Characterization of 6-Hydroxytryptamine in the Rat Midbrain by Using Specific Antibodies

The visualization of serotonin, 5-methoxytryptamine, and tryptamine in the rat midbrain has been made possible by the development of antibodies raised against these conjugated molecules. It has been suggested that 6-hydroxytryptamine (6-HT) might also be a neurotransmitter in this region. To test this hypothesis, 6-HT was synthesized and antibodies were raised in the rabbit. The high avidity (IC50 = 5 x 10(-9) M) and specificity [cross-reactivity ratio between 6-HT-glutaraldehyde (G)-bovine serum albumin (BSA) and 5-HT-G-BSA, the most immunoreactive compound, was 1,500] rendered these antibodies reliable tools for specific molecular detection of 6-HT in the G-fixed tissues. In the dopaminergic region, 6-HT immunoreactivity was noted in the substantia nigra but was particularly intense in the red nuclei, where it seems to be localized in the magnocellular division in the form of large 6-HT neurons. In contrast, there were few 6-HT neurons in the raphe nuclei. Thus, 6-HT may be a new putative neurotransmitter existing in the red nuclei, in addition to the other neurotransmitters already described in this region, in the nigro-rubral pathway, and in the rubral projection from the dorsal raphe nuclei. 6-HT is possibly implicated in motor control and might exert hallucinogenic properties as do other 6-hydroxylated indoleamines.

Distribution, morphology and number of monoamine-synthesizing and substance P-containing neurons in the human dorsal raphe nucleus

The distribution, morphology and number of serotonin-, catecholamine- and substance P-containing neurons in the human dorsal raphe nucleus were studied. Parallel series of sections were prepared from 10 human brainstems obtained at autopsy from patients without neurological disease aged between 42 and 88 years. The neurons were identified using immunohistochemistry with antibodies raised against phenylalanine hydroxylase (tryptophan hydroxylase-containing, serotonin neurons), tyrosine hydroxylase (catecholamine neurons) and substance P. A reference series of Nissl-stained sections was also prepared and data published separately were used to delineate the subnuclear divisions of the dorsal raphe nucleus and to establish the total number of neurons in each subnucleus. The following principal findings emerged. (1) Serotonin-synthesizing neurons are present in all regions of the dorsal raphe nucleus and their total number is 165,000 +/- 34,000. The same types of neurons as those seen in Nissl material characterize each of the five subnuclei (caudal, dorsal, ventral, ventrolateral and interfascicular). (2) Substance P-containing neurons mostly occupy the rostral part of the nucleus and their number is 74,600 +/- 17,600. (3) Catecholamine cells are only found in the rostral part of the dorsal raphe nucleus and their number is 5600 +/- 3400. (4) In the ventral and interfascicular subnuclei the combined number of serotonin-synthesizing and substance P-containing neurons exceeds the total number of Nissl-stained neurons suggesting that serotonin and substance P co-exist in a substantial part of the cell population of the dorsal raphe nucleus. This is further supported by the highly similar morphology and size of these neurons. It is concluded that there are demonstrable chemical differences between the various subregions of the human dorsal raphe nucleus. These differences are in harmony with the results of hodological studies in animals, which have demonstrated differential projection pathways emerging from this nucleus.

Immunohistochemistry of endogenous L-DOPA in the rat posterior hypothalamus

The aim of this work was to study L-DOPA-containing neuronal structures of the rat posterior and dorsal hypothalamus by means of immunohistochemistry using antiserum against glutaraldehyde conjugated L-DOPA. Aspects and distribution of L-DOPA immunoreaction among cells of the supramammillary nucleus and the A11, A13c and A13 cell groups are described and compared to dopamine immunoreactivity, mainly through a double colored labelling procedure employing a color modification of the DAB reaction by metallic ions. Differences between L-DOPA and dopamine stainings within cell groups as the presence of cells with predominant or exclusive L-DOPA coloration are tentatively explained under the light of previous findings using immunohistochemistry of catecholamines synthesizing enzymes and catecholamines histofluorescence.

Simultaneous detection of tryptamine and dopamine in rat substantia nigra and raphe nuclei using specific antibodies

Using a double-labelling procedure, morphological relationships existing between dopaminergic and indoleaminergic neuronal systems in the rat brain were investigated. First, thanks to a tryptamine (T) antiserum, we visualized this indoleamine in all mesencephalic regions and showed that the T-immunoreactivity (IR) seems to overlap with the stainings observed from serotonin and 5-methoxytryptamine antisera. Secondly, using a monoclonal anti-dopamine (DA) antibody and our anti-T antibodies, the simultaneous and specific detection of these compounds enabled us to define the spatial relationships existing between the dopaminergic and tryptaminergic neuronal systems from the substantia nigra (SN) to the raphe nuclei. No co-localization existed, but the intensity of T-IR decreased from back to front, whereas the DA-staining decreased in the opposite way, indicating possible interactions at the end of the SN and the B9 area.

Monoclonal antibody directed against glutaraldehyde conjugated glutamate and immunocytochemical applications in the rat brain

Like other small-sized neurotransmitter molecules, glutamate (Glu) was conjugated to carrier proteins via glutaraldehyde (G). Human serum albumin (HSA) and thyroglobulin (TH) conjugates were alternately injected into mice. When a relevant immune response was obtained for antibody affinity and specificity, hybridization of spleen activated lymphocytes with SP2/O/Ag myeloma cells was performed. Supernatant culture media of hybridomas were tested for the presence of anti-conjugated Glu antibodies with our ELISA method. Selected hybridomas giving good antibody affinity and specificity were then cloned by the limiting dilution technique. Using DEAE-chromatographed ascites fluid, Glu reactivity was observed on the cortex and the hippocampus. Staining obtained with this monoclonal antibody was in agreement with that observed with previous polyclonal antisera directed against conjugated Glu or monoclonal anti-gamma-glutamyl-Glu antibody.

Identification of L-dopa-dopamine and L-dopa cell bodies in the rat mesencephalic dopaminergic cell systems

An immunocytochemical technique for simultaneously visualizing two different antigens, dihydroxyphenylalanine (L-DOPA) and dopamine (DA), has been used to investigate the presence of cell bodies containing both compounds L-DOPA and DA and those having only L-DOPA in rat mesencephalon areas. The brain slices were processed with a double peroxidase-antiperoxidase method using simultaneously an incubation of a rabbit anti-L-DOPA serum and a monoclonal anti-DA antibody raised in mouse. Both antigens were revealed by the peroxidase reaction but with different chromogens that are easily distinguishable. In this staining procedure, the first antigen, conjugated DA was stained using the 3,3'-diaminobenzidine (DAB)-Nickel complex; while the second antigen, conjugated L-DOPA, was localized using DAB. The yellow-brown color due to DAB was masked by that of DAB-nickel. The possible existence of both single and double labelings could be worked. We have found many L-DOPA-positive/DA-positive and a few L-DOPA-positive/DA-negative cell bodies in dopaminergic regions in the rat midbrain: substantia nigra, ventral tegmental area, and raphe nuclei. In the locus coeruleus, we noted only L-DOPA-positive/DA-positive cell bodies. These results confirm those previously described for rat and cat hypothalamus, where both immunoreactive-cell body types have been detected: L-DOPA positive/DA positive and L-DOPA positive/DA negative. The existence of neuronal cells containing only L-DOPA is a new neuroanatomic finding, accounting better for the heterogeneity of dopamine systems with respect to physiologic, pharmacologic, and molecular data.