Serotonergic Cell Bodies Research Articles

Spontaneous activity in the developing mouse midbrain driven by an external pacemaker

Central nervous system (CNS) development depends upon spontaneous activity (SA) to establish networks. We have discovered that the mouse midbrain has SA expressed most robustly at embryonic day (E) 12.5. SA propagation in the midbrain originates in midline serotonergic cell bodies contained within the adjacent hindbrain and then passes through the isthmus along ventral midline serotonergic axons. Once within the midbrain, the wave bifurcates laterally along the isthmic border and then propagates rostrally. Along this trajectory, it is carried by a combination of GABAergic and cholinergic neurons. Removing the hindbrain eliminates SA in the midbrain. Thus, SA in the embryonic midbrain arises from a single identified pacemaker in a separate brain structure, which drives SA waves across both regions of the developing CNS. The midbrain can self-initiate activity upon removal of the hindbrain, but only with pharmacological manipulations that increase excitability. Under these conditions, new initiation foci within the midbrain become active. Anatomical analysis of the development of the serotonergic axons that carry SA from the hindbrain to the midbrain indicates that their increasing elongation during development may control the onset of SA in the midbrain.

Acute effects of combining citalopram and pindolol on regional brain serotonin synthesis in sham operated and olfactory bulbectomized rats

The olfactory bulbectomized (OBX) rat is considered to be a good model of the pathology of human depression and also of the functional actions of antidepressant drug therapy. It has been proposed that antidepressant effects of selective serotonin reuptake inhibitors (SSRIs) can be accelerated by blocking 5-HT 1A/B autoreceptors with pindolol. The underlying mechanism is thought to involve acute unrestricting of 5-HT release and, consequently, relatively enhanced 5-HT turnover throughout the forebrain serotonergic networks. The effect of this combination on 5-HT turnover in sham operated or OBX rats can be assessed at the level of 5-HT synthesis, a very important presynaptic step in serotonergic neurotransmission, using the α-[ 14C]methyl- l-tryptophan autoradiography method. In sham rats, acute citalopram (20 mg/kg) treatment increased synthesis at almost all serotonergic terminal regions but slightly decreased synthesis at serotonergic cell body regions (i.e. dorsal and median (not significant) raphe; ∼16%). Combining pindolol (10 mg/kg) with citalopram further increased synthesis at many regions in sham rats (relative to treatment with only citalopram). In OBX rats, citalopram decreased synthesis at a few terminal regions and greatly decreased synthesis at the dorsal and median raphe (∼45%; relative to OBX rats treated with saline). Combining pindolol with citalopram greatly increased synthesis at almost all regions in OBX rats (relative to treatment with only citalopram). These results suggest that acute citalopram effects result in elevated terminal 5-HT synthesis, but these effects are restrained by 5-HT 1A/B autoreceptor feedback to different degrees in sham and OBX rats. Moreover, 5-HT 1A/B autoreceptor feedback is stronger in OBX rats and may underlie the delay of SSRI effects in OBX rats and, correspondingly, in human depression. Pindolol acceleration and augmentation of SSRI antidepressant therapy for human depression may be mediated by attenuation of 5-HT 1A/B autoreceptor feedback, permitting unhindered SSRI effects on serotonergic terminals.

Age‐ and subcaste‐related patterns of serotonergic immunoreactivity in the optic lobes of the ant Pheidole dentata

Serotonin, a biogenic amine known to be a neuromodulator of insect behavior, has recently been associated with age-related patterns of task performance in the ant Pheidole dentata. We identified worker age- and subcaste-related patterns of serotonergic activity within the optic lobes of the P. dentata brain to further examine its relationship to polyethism. We found strong immunoreactivity in the optic lobes of the brains of both minor and major workers. Serotonergic cell bodies in the optic lobes increased significantly in number as major and minor workers matured. Old major workers had greater numbers of serotonergic cell bodies than minors of a similar age. This age-related increase in serotonergic immunoreactivity, as well as the presence of diffuse serotonin networks in the mushroom bodies, antennal lobes, and central complex, occurs concomitantly with an increase in the size of worker task repertoires. Our results suggest that serotonin is associated with the development of the visual system, enabling the detection of task-related stimuli outside the nest, thus playing a significant role in worker behavioral development and colony-wide division of labor.

Neural architecture of the brachiolaria larva of the starfish, Asterina pectinifera

The nervous system of the brachiolaria larva of the starfish, Asterina pectinifera, was characterized using immunohistochemistry with the neuron-specific monoclonal antibodies 1E11 and 1F9 and an anti-serotonin antibody. The antigen recognized by 1F9 was determined by immunoprecipitation, peptide identification by mass spectrometry, and cDNA cloning as a novel START (steroidogenic acute regulatory protein [StAR]-related lipid transfer) domain-containing protein. Nerve cells are prominent in the brachiolar arms, ciliary bands, and adult rudiment. The brachiolar arms contain sensory-like nerve cells in the adhesive papillae, flask-shaped nerve cells in the adhesive disk, and bundles of fibers with branches interconnecting them. In the ciliary bands, nerve cells are interconnected with axon bundles along the ciliary bands and some neurons send fibers toward the oral and aboral epidermis. These neural components of the ciliary bands are regionally modified to form masses such as lateral and oral ganglia. The future aboral epidermis of the adult rudiment forms a nerve plexus with cell bodies enriched over spicules. Serotonergic nerve cell bodies are found throughout the nervous system except in the adhesive disk, the bipinnaria arms, and the adult rudiment. In addition, there are neural components in the esophagus and in the coelom where nerve fibers or bundles have distinct orientations with respect to the muscle fibers. The neuroanatomy of the brachiolaria suggests how it may function in controlling larval physiology and identifies intriguing problems on the origin of larval and adult nerves.

Flesinoxan challenge suggests that chronic treatment with paroxetine in rats does not desensitize receptors controlling 5-HT synthesis

It has been proposed that the desensitization of 5-HT 1A (5-hydroxytryptamine; serotonin) receptors following chronic therapy with selective serotonin reuptake inhibitors (SSRIs) is necessary for their therapeutic efficacy. Stimulation of the 5-HT 1A receptors decreases serotonin (5-HT) synthesis and release, but it is not clear if the receptors are fully desensitized following chronic SSRI treatment. The main objective of this study was evaluation of ability of 5-HT 1A receptors to modulate 5-HT synthesis after 14-day paroxetine treatment. 5-HT 1A receptor sensitivity following chronic administration of the SSRI paroxetine was assessed by the ability of an acute challenge with the 5-HT 1A agonist, flesinoxan, to modulate 5-HT synthesis in the rat brain. The rates of 5-HT synthesis were measured using the α-[ 14C]methyl- l-tryptophan autoradiographic method. The rats were treated for 2 weeks with paroxetine (10 mg/(kg day), s.c., delivered by osmotic minipump). After this treatment, the rats received an acute challenge with flesinoxan (5 mg/kg, i.p.), while the control rats were injected with the vehicle. Forty minutes following the flesinoxan injection, the tracer, α-[ 14C]methyl- l-tryptophan, was injected over 2 min. 5-HT synthesis rates were calculated from autoradiographically measured tissue tracer concentrations and plasma time–activity curves. The results demonstrated that the acute flesinoxan challenge produced a significant decrease in 5-HT synthesis rates throughout the rat brain. The greatest decrease was observed in the ventral hippocampus, somatosensory cortex and the ascending serotonergic cell bodies. In comparison with data reported on an acute challenge with flesinoxan in naïve rats (rats without any other treatment), the results presented here suggest a greater effect of flesinoxan on synthesis reduction in rats chronically treated with paroxetine. The results also suggest that the 5-HT receptors were not fully desensitized by paroxetine treatment, and that the stimulation of 5-HT 1A receptors with an agonist is still capable of reducing 5-HT synthesis.

Increased expression of tyrosine hydroxylase and anomalous neurites in catecholaminergic neurons of ATF‐2 null mice

ATF-2/CRE-BP1 was originally identified as a cAMP-responsive element (CRE) binding protein abundant in the brain. We previously reported that phosphorylation of ATF-2 increased the expression of tyrosine hydroxylase (TH), which is the rate-limiting enzyme for catecholamine biosynthesis, directly acting on the CRE in the promoter region of the TH gene in PC12D cells (Suzuki et al. [2002] J. Biol. Chem. 277:40768-40774). To examine the role of ATF-2 on transcriptional control of the TH gene in the brain, we investigated the TH expression in ATF-2-/- mice. We found that TH expression was greatly increased in medulla oblongata and locus ceruleus of the ATF-2-deficient embryos. Ectopic expression of TH was observed in the raphe magnus nucleus, where serotonergic neural cell bodies are located. Interestingly, A10 dorsal neurons were lost in the embryos of ATF-2-/- mice. There was no difference in the TH immunoreactivity in the olfactory bulb. The data showed that alteration in TH expression by absence of ATF-2 gradually declined from caudal to rostral part of the brain. We also found anomalous neurite extension in catecholaminergic neurons of ATF-2 null mice, i.e., increased dendritic arborization and shortened axons. These data suggest that ATF-2 plays critical roles for proper expression of the TH gene and for neurite extension of catecholaminergic neurons, possibly through a repressor-like action.

The nervous system of Convolutriloba (Acoela) and its patterning during regeneration after asexual reproduction

We describe the serotonergic and cholinergic nervous system of the asexually reproducing acoel Convolutriloba longifissura Bartolomaeus & Balzer, 1997 by means of immunohistochemistry, conventional histochemistry and transmission electron microscopy. Immunocytochemical staining for serotonin revealed neurons in the brain, in a pair of ventral main longitudinal cords, in two pairs of smaller dorsal longitudinal nerve cords, and in a submuscular nerve net. The brain comprises a ventral-anterior commissure and a less intensely stained dorsal commissure joined together by connectives into a three-ringed scaffold from which the longitudinal nerves extend. We followed the regeneration of the serotonergic part of the nervous system up to the second day after fission. Within this time period, the offspring reestablished bilateral symmetry in the nervous system and developed full motor control. The presence of aminergic cell bodies associated with the main lateral nerve cords of C. longifissura shows that the acoelan nervous system is more similar to that of other platyhelminths (triclads, rhabditophorans) than previously assumed. The presence of serotonergic cell bodies along the main nerve cord correlates with the capacity for asexual reproduction via fissioning. We also describe the single fission mode of C. hastifera Winsor 1990, which brings the modes of asexual reproduction employed by members of the Convolutrilobinae to three.

Localization of l-DOPA uptake and decarboxylating neuronal structures in the cat brain using dopamine immunohistochemistry

The present study examined dopamine-immunoreactive neuronal structures using immunohistochemistry in conjunction with an anti-dopamine antiserum, following injection of l-3,4-dihydroxyphenylalanine ( l-DOPA) with or without an inhibitor of monoamine oxidase (Pargyline) in the cat brain. l-DOPA injection made it possible to detect dopamine immunoreactivity in presumptive serotonergic and noradrenergic cell bodies and axons. Weak to moderate dopamine immunoreactivity was observed in non-aminergic cells (possibly so-called “D” cells containing aromatic l-amino acid decarboxylase (AADC)) in several hypothalamic, midbrain, pontine and medullary nuclei. Intense dopamine immunoreactivity became visible in a large number of cells and axons (possibly containing AADC) with wide distribution in the brain following administration of l-DOPA with Pargyline. AADC is most likely active in cells and axons that take up l-DOPA, where it decarboxylates the l-DOPA to dopamine. However, newly synthesized dopamine in such cells is rapidly oxidized by monoamine oxidase.

Regulation of Serotonin-1A Receptor Function in Inducible Brain-Derived Neurotrophic Factor Knockout Mice After Administration of Corticosterone

We examined the effects of a forebrain-specific reduction in brain-derived neurotrophic factor (BDNF) on the regulation of serotonin-1A (5-HT1A) receptor function in serotonergic cell body areas as well as in limbic and cortical structures of mice chronically treated with corticosterone. 5-HT1A receptor function, at the level of receptor-G protein interaction, was assessed with quantitative autoradiography of [35S]GTPgammaS binding stimulated by the 5-HT1A receptor agonist 8-OH-DPAT. 5-HT1A receptor number was assessed by measuring the binding of the antagonist radioligand [3H] WAY100635. We observed a significant attenuation of 5-HT1A receptor function, in the absence of a change in receptor number, in the dorsal hippocampus of BDNF knockout versus control mice. There was no difference between control and BDNF knockout mice in 5-HT1A receptor number or function in the dorsal or median raphe nuclei or medial prefrontal cortex or anterior cingulate cortex. Corticosterone treatment of control mice decreased 5-HT1A receptor function in the dorsal and median raphe but not in hippocampus or frontal cortical areas. The regulation of 5HT1A receptor number or function in the dorsal and median raphe by corticosterone was lost in BDNF knockout mice. Attenuation of BDNF expression in forebrain regions produces differential effects on distinct 5-HT1A receptor populations and on the regulation of these receptor populations by corticosterone.

Prefrontal cortex dysfunction in patients with suicidal behavior

Abnormal serotonergic neurotransmission has long been demonstrated in suicidal behavior. The dorsal and median raphe nuclei housing the main serotonergic cell bodies and the prefrontal cortex (PFC), particularly the ventral part innervated by the serotonergic system, have therefore been studied extensively in suicidal behavior research. However, only a few studies have described neuropsychological function impairment in suicidal patients. We investigated PFC-related neuropsychological function in patients with suicidal behavior, separating dorsolateral PFC (DLPFC)- and orbitofrontal cortex (OFC)-related functions. We compared 30 euthymic patients with suicidal behavior aged 18-65 years with 39 control subjects, for the following neuropsychological domains: global intellectual functioning, reward sensitivity, initiation, inhibition, and working memory. Patients and controls were compared by means of univariate and multivariate analyses, adjusting for age at interview, level of education and mood state at the time of evaluation. Trait impulsivity, measured with the Barratt Impulsivity Scale version 10 (BIS-10), was also included as a covariate in a subset of analyses. Multivariate comparisons demonstrated significant executive function deficits in patients with suicidal behavior. In particular, we observed impairment in visuospatial conceptualization (p<0.0001), spatial working memory (p=0.001), inhibition (Hayling B-A, p=0.04; go anticipations, p=0.01) and visual attention (or reading fluency) (p=0.002). Similar results were obtained following adjustment for motor impulsivity as a covariate, except for spatial working memory. These deficits are consistent with prefrontal dysfunction in patients with suicidal behavior. Differentiation between DLPFC- and OFC-related neuropsychological functions showed no specific dysfunction of the orbitofrontal region in patients with suicidal behavior in our sample.

Mirtazapine-Induced Nightmares

Sir: Mirtazapine is classed as a noradrenergic and specific serotonergic antidepressant (NaSSA). It acts by blocking α2 receptors on noradrenergic neurons and enhancing norepinephrine release.1 Increased levels of norepinephrine act on α1-adrenoceptors on serotonergic cell bodies, increasing serotonergic firing.1 Nightmares occur only in rapid eye movement (REM) sleep. Most antidepressants suppress REM sleep; hence, nightmares are not a commonly reported side effect of therapy with antidepressants. We report the first ever case, to our knowledge, of a patient who developed severe nightmares on initiation of therapy with mirtazapine, which necessitated stopping the drug. Case report. Mr. A, a 52-year-old white man, presented in 2006 with depressive symptoms including low mood, poor sleep and appetite, loss of weight, hopelessness, and fatigue. Because of his symptom profile, he was started on mirtazapine, 15 mg at night. One day later, he reported vivid nightmares of being murdered and his body being cut up. These nightmares woke him from sleep and left him feeling very scared and upset. He recalled that he had been treated with mirtazapine 2 years ago and it had to be discontinued because of similar distressing nightmares. After 4 days of therapy and experiencing nightmares every night, he requested that the medication be stopped. The nightmares disappeared 1 day after cessation of mirtazapine. He denied ever experiencing such distressing nightmares in the past, except when he was taking mirtazapine. His only other concurrent medication was hydroxymorphone. The temporal relationship between the initiation of treatment with mirtazapine and onset of nightmares and their disappearance with discontinuation of the drug, and also their occurrence during a previous episode of mirtazapine treatment, suggest a causal etiology. Most antidepressants suppress REM sleep.2 Mirtazapine has been shown to increase REM sleep even with acute administration, i.e., at 2 days.3 It has also been shown to increase total sleep time, sleep efficiency, and stage 2 and slow wave sleep. These effects persisted after 5 weeks of treatment.3 Vivid dreams and nightmares have been reported with other antidepressants that increase REM sleep, such as bupropion.4 It is possible that mirtazapine increased REM sleep in this patient, which may have induced nightmares. Clinicians should be aware of this side effect, as it can potentially affect treatment adherence.

The role of noradrenergic tone in the dorsal raphe nucleus of the mouse in the acute behavioral effects of antidepressant drugs

Serotonin neurons of the dorsal raphe nucleus (DRN) receive dense noradrenergic innervation and are under tonic activation by noradrenergic input. Thus, afferent noradrenergic input to the DRN could modify the antidepressant effects of selective serotonin reuptake inhibitors (SSRIs) by regulating serotonergic transmission. This study investigated whether noradrenergic innervation of the DRN contributes to the acute behavioral effects of different types of antidepressant drugs in the mouse tail suspension test (TST). Noradrenergic terminals in the DRN were destroyed selectively by the local application of 6-hydroxydopamine (6-OHDA). Immunohistochemical analysis confirmed the presence of noradrenergic fibers in the mouse DRN, that 6-OHDA-induced destruction of noradrenergic terminals was confined to the DRN, and serotonergic cell bodies were not affected by 6-OHDA treatment. The antidepressants tested included the SSRIs, fluoxetine and citalopram, and the norepinephrine reuptake inhibitor (NRI) desipramine. The behavioral effects of fluoxetine (20 mg/kg, IP) were blocked by the destruction of noradrenergic terminals. In contrast, pretreatment with 6-OHDA did not alter the ability of citalopram (20 mg/kg, IP) or desipramine (10 mg/kg, IP) to reduce immobility in the TST. Destruction of noradrenergic projections from the locus ceruleus (LC) by DSP-4 treatment did not alter the behavioral effects of any of the antidepressants tested, or the presence of noradrenergic terminals in the DRN, thus indicating that noradrenergic pathways originating from the LC do not mediate the acute behavioral effects of antidepressants in this test. Thus, afferent noradrenergic activity at the level of the DRN can modulate serotonergic transmission in forebrain structures and the behavioral effects of SSRIs, such as fluoxetine, which use noradrenergic input to the DRN to increase forebrain serotonin.

Serotonin noradrenaline reuptake inhibitors: New hope for the treatment of chronic pain

Depression and painful symptoms occur frequently together. Over 75% of depressed patients report painful symptoms such as headache, stomach pain, neck and back pain as well as non-specific generalized pain. In addition, World Health Organization data have shown that primary care patients with chronic pain have a four fold greater risk of becoming depressed than pain-free patients. Increasingly, pain is considered as an integral symptom of depression and there evidence to suggest that pain and depression may arise from a common neurobiological dysfunction. Serotonergic cell bodies, in the raphe nucleus, and noradrenergic cell bodies in the locus coeruleus send projections to various parts of the brain, where they are involved in the control of mood, movement, cognitive functioning and emotions. In addition both serotonergic and noradrenergic neurons project to the spinal cord. These descending pathways serve to inhibit input from the intestines, skeletal muscles and other sensory inputs. Usually, these inhibitory effects are modest, but in times of stress, in the interest of the survival of the individual, they can completely inhibit the input from painful stimuli. A dysfunction of the serotonergic and noradrenergic neurons can thus affect both the ascending and descending pathways resulting in the psychological symptoms of depression and somatic pain symptoms such as chronic pain, fibromyalgia, non-cardiac chest pain, or irritable bowel syndrome. In view of this, it is not surprising that tricyclic antidepressants have been a standard treatment of chronic pain for many years. In contrast and in spite of their improved tolerance, selective serotonin reuptake inhibitors do not appear to be particularly effective in the treatment of pain. Recently, a number of open and controlled trials with selective serotonin and noradrenaline reuptake inhibitors such as venlafaxine, milnacipran and duloxetine, suggest that these compounds may be more effective in relieving pain than selective inhibitors of serotonin reuptake. Wherever valid comparisons have been made the newer dual action drugs appear to be as effective as the tricyclic and considerably better tolerated. Dual action antidepressants may thus soon become the new standard treatment of chronic pain whether it is associated with depression or not. In addition, these agents may also have a role in modulating neurogenesis and other neuroplastic changes in the central nervous system, thereby leading to more complete recovery in patients suffering from the symptoms of depression or chronic pain.

The high specific activity tritium labeling of the ganglion-blocking nicotinic antagonist chlorisondamine

Chlorisondamine is a bisquaternary ganglion-blocking nicotinic antagonist that accumulates in dopaminergic, serotonergic, and noradrenergic cell bodies; the mechanism of uptake and time-course of retrograde transport are not known. Chlorisondamine could possibly be taken into monoaminergic neurons when blocked nicotinic receptors on those cells are internalized. In order to more easily study the mechanism of the capture and recycling of chlorisondamine, a ligand is needed that has high specific activity. For that purpose, we now report the preparation of 3H-labeled chlorisondamine (4,5,6,7-tetrachloro-2-[3H]methyl-2-(2-trimethylammoniumethyl)-isoindolinium diiodide) of high specific activity (94 Ci/mmol). The compound was synthesized by quarternization of 4,5,6,7-tetrachloro-2-(2-trimethylammoniumethyl-isoindolinium iodide with pertritiated methyl iodide in dimethylformamide at high temperature in a sealed vessel. Copyright © 2006 John Wiley & Sons, Ltd.

Chronic administration of venlafaxine fails to attenuate 5-HT1A receptor function at the level of receptor-G protein interaction

In this study venlafaxine was administered to rats at a low, moderate or high dose; for comparison, the selective serotonin reuptake inhibitor (SSRI) sertraline and the tricyclic antidepressant (TCA) amitriptyline were also included. We evaluated, using quantitative autoradiography, the effect of these antidepressant treatments on [35S]GTPgammaS binding stimulated by the 5-HT1A receptor agonist 8-OH-DPAT, a measure of the capacity of 5-HT1A receptors to activate G proteins. Chronic administration of amitriptyline resulted in a marked increase in 5-HT1A receptor-stimulated [35S]GTPgammaS binding in the hippocampus which was accompanied by an increase in 5-HT1A receptor number. 5-HT1A receptor-stimulated [35S]GTPgammaS binding in the hippocampus was also increased by chronic treatment with the highest dose of venlafaxine; 5-HT1A receptor number, however, was not significantly altered. In serotonergic cell body areas (i.e. dorsal and median raphe nuclei), 5-HT1A receptor-stimulated [35S]GTPgammaS binding was not altered by chronic administration of amitriptyline, sertraline or venlafaxine. Chronic TCA treatment does not desensitize somatodendritic 5-HT1A autoreceptor function. However, the lack of effect of chronic sertraline treatment on 5-HT1A receptor-stimulated [35S]GTPgammaS binding is in contrast to what has been observed previously following chronic administration of the SSRI fluoxetine, and suggests that different SSRIs may regulate somatodendritic 5-HT1A autoreceptor function differently depending on their pharmacology. Our data also suggest that the desensitization of somatodendritic 5-HT1A autoreceptors observed in electrophysiological studies following chronic venlafaxine administration is not at the level of receptor-G protein interaction. The hypothermic response in vivo to acute injection of 8-OH-DPAT was significantly attenuated following chronic treatment with venlafaxine or sertraline, but not amitriptyline.

Comparison of the serotonergic nervous system among Tunicata: implications for its evolution within Chordata

Using immunohistochemistry in combination with confocal laser scanning microscopy, the serotonergic nervous systems of major tunicate taxa were studied in three-dimensional detail. Organisms analyzed included aplousobranchiate, phlebobranchiate, and stolidobranchiate ascidian larvae, appendicularian juveniles and adults, and doliolid oozooids. Outgroup comparisons to notochordates showed that the serotonergic nervous system of the last common ancestor of Chordata consisted of two elements: (i) an anterior concentration of serotonergic cell bodies, and (ii) a fiber network that followed posteriorly and gave rise to fiber tracts that descended towards the effective somatic lateral musculature. Within Tunicata, the nervous systems of Appendicularia and Aplousobranchiata appear serotonin-reduced or negative. This could be interpreted as a heterochronic reduction and a synapomorphy between Appendicularia and Aplousobranchiata. In this hypothesis, free-living Appendicularia are derived within Tunicata, and a biphasic life cycle with a free-swimming larva and a sessile, ascidian-like adult is most parsimoniously reconstructed for the last common ancestor of Tunicata. The close spatial relation of the serotonergic cell cluster with the statocyte complex suggests a function as an integrative control center for the coordination of locomotion. A similar anterior concentration of serotonergic nerve cells is known from tornaria larvae. See also Electronic Supplement at: http://www.senckenberg.de/odes/05-02.htm

Immunohistological characterization of striatal and amygdalar structures in the telencephalon of the fire-bellied toad bombina orientalis

The subpallium of the fire-bellied toad Bombina orientalis was studied by means of enzyme-histological detection of NADPH-diaphorase and immunohistological demonstration of aspartate, GABA, calretinin, choline-acetyl transferase, Leu-and Met-enkephalin, neuropeptide Y, 5-hydroxy-tryptamine (serotonin), somatostatin, substance P and tyrosine-hydroxylase. As in other vertebrates, the striato-pallidum is characterized by GABA-, substance P- and enkephalin-immunoreactivity. Neurons and fibers differing in immunoreactivity are arranged in layers. Choline-acetyl transferase-immunoreactive neurons were found in a position corresponding to the mammalian cholinergic cell-group (Ch4-group), which therefore may be homologous to the nucleus basalis of Meynert. Within the amygdaloid complex, the cortical and lateral (vomeronasal) nuclei are similar in calretinin-, GABA-, NADPH-diaphorase-, enkephalin, substance P- and neuropeptide Y-(immuno)histology. The medial and central amygdaloid nuclei reveal a dense peptidergic innervation, and the medial amygdala additionally exhibits serotonergic fibers and cell bodies staining for neuropeptides and tyrosine-hydroxylase. Differences between Bombina and other anuran species exist, such as the absence of cholinergic neurons in the striatum. Our findings corroborate the view based on recent studies on the hodology and cytoarchitecture of the anuran telencephalon that the anuran ventral telencephalon contains most of the structures found in the mammalian brain. This concerns a septal region, a dorsal and ventral striato-pallidum including a nucleus accumbens and an amygdaloid complex consisting of a central, cortical and vomeronasal amygdala. The only major difference appears to concern the lack of a basolateral amygdala.

Rat brain serotonin neurones that express neuronal nitric oxide synthase have increased sensitivity to the substituted amphetamine serotonin toxins 3,4-methylenedioxymethamphetamine and p-chloroamphetamine

Substituted amphetamines such as p-chloroamphetamine and the abused drug methylenedioxymethamphetamine cause selective destruction of serotonin axons in rats, by unknown mechanisms. Since some serotonin neurones also express neuronal nitric oxide synthase, which has been implicated in neurotoxicity, the present study was undertaken to determine whether nitric oxide synthase expressing serotonin neurones are selectively vulnerable to methylenedioxymethamphetamine or p-chloroamphetamine. Using double-labeling immunocytochemistry and double in situ hybridization for nitric oxide synthase and the serotonin transporter, it was confirmed that about two thirds of serotonergic cell bodies in the dorsal raphé nucleus expressed nitric oxide synthase, however few if any serotonin transporter immunoreactive axons in striatum expressed nitric oxide synthase at detectable levels. Methylenedioxymethamphetamine (30mg/kg) or p-chloroamphetamine (2×10mg/kg) was administered to Sprague–Dawley rats, and 7 days after drug administration there were modest decreases in the levels of serotonin transporter protein in frontal cortex, and striatum using Western blotting, even though axonal loss could be clearly seen by immunostaining. p-Chloroamphetamine or methylenedioxymethamphetamine administration did not alter the level of nitric oxide synthase in striatum or frontal cortex, determined by Western blotting. Analysis of serotonin neuronal cell bodies 7 days after p-chloroamphetamine treatment, revealed a net down-regulation of serotonin transporter mRNA levels, and a profound change in expression of nitric oxide synthase, with 33% of serotonin transporter mRNA positive cells containing nitric oxide synthase mRNA, compared with 65% in control animals. Altogether these results support the hypothesis that serotonin neurones which express nitric oxide synthase are most vulnerable to substituted amphetamine toxicity, supporting the concept that the selective vulnerability of serotonin neurones has a molecular basis.

Understanding pain in depression.

A dysfunction of the serotonergic and noradrenergic pathways is commonly accepted as playing a major role in the aetiology of depression. Serotonergic cell bodies, located in the raphe nucleus, send projections to various parts of the brain where they are involved in the control of mood, movement, emotions such as anxiety and regulate behaviours such as eating, sexual activity and the feeling of pleasure. Similarly, the noradrenergic neurons, located in the locus coeruleus, project to the same regions where they regulate, in addition, attention and cognition. A further projection to the cerebellum regulates motor control. A dysfunction at the level of the monoamine neurons thus results in the classical symptoms of depression. In addition to these ascending pathways, however, the neurons in the raphe nucleus and the locus ceruleus also project to the spinal cord. These descending pathways serve to inhibit input from the intestines, the skeletal muscles and other sensory inputs. Under normal conditions, these inhibitory effects are modest, but in times of stress, in the interests of the survival of the individual, they can completely inhibit the input from painful stimuli. A dysfunction at the level of the serotonergic and noradrenergic neurons can thus affect both the ascending and descending pathways resulting in the psychological and somatic symptoms of depression but also in physical painful symptoms.

Serotonergic neurotransmission in the bivalve Venus verrucosa (Veneridae): a neurochemical and immunohistochemical study of the visceral ganglion and gonads

Serotonin (5-hydroxytryptamine, 5-HT) is well known to be involved in many aspects of bivalve biology, especially in the control of reproductive function. In this work, a neurochemical and immunohistochemical study was carried out in the visceral ganglion of Venus verrucosa (Bivalvia: Veneridae), with the aim of elucidating the features of 5-HT neurotransmission and its influence on gamete emission in this poorly investigated bivalve species. 5-HT release was characterized: tritium efflux, evoked from the isolated [3H]5-HT-preincubated visceral ganglion by high potassium concentrations, was shown to possess the characteristics of neurotransmitter release (sodium and calcium dependence, auto-feedback regulation). Serotonergic cell bodies and axonal tracts were labeled by immunohistochemistry, confirming that the released 5-HT originates in a pool of neurons in the visceral ganglion. The presence and distribution of serotonin were immunohistochemically checked in the gonads as well. A plexus of immunopositive fibers was observed in the gonadic tissue of both sexes, specifically located in the follicle walls, and this innervation appeared to come from branching of the cerebro-visceral connectives, whereas no peripheral serotonergic neurons were identified. The immunohistochemical data were supported by light and electron microscope observations. Exogenous 5-HT was applied to V. verrucosa specimens by intramuscular injection; it induced spawning in both sexes, and the response rate was significantly higher in males than in females, as previously observed in some other species of gonochoric bivalves. These findings suggest the existence of a serotonergic neurotransmission in V. verrucosa, possibly regulating the reproductive process.