5HT Neurons Research Articles

Distribution of serotonin-immunoreactive nerve cells and fibers in the rat gastrointestinal tract.

The distribution of serotonin-immunoreactive (5HT-IR) nerve cells and fibers was thoroughly investigated immunohistochemically in the rat stomach, duodenum, jejunum, ileum, and colon. The immunoreactivity of the 5HT neurons was compared between non-treated controls and animals treated with colchicine, colchicine plus 5-hydroxytryptophan (5HTP), colchicine plus pargyline, and reserpine. The intensity of immunoreactivity in nerve fibers as well as nerve cell bodies was enhanced mostly in colchicine plus pargyline treated animals, therefore these animals were used for an observation of precise localization of 5HT in the rat gastrointestinal (GI) tract. Immunoreactivity in the nerve cell bodies and fibers was completely abolished in the GI tract of reserpine treated animals. The pattern of localization and projection of 5HT-IR neurons was similar in all segments of the rat GI tract: 5HT-IR nerve cell bodies were located in the myenteric plexus and showed the distinctive features of Dogiel type I neurons. Prominent bundles of varicose fibers traversed the myenteric ganglia and some of them surrounded the cell bodies of immunopositive and immunonegative neurons. 5HT-IR nerve fibers were located in the submucous plexus, densely entwined about the submucosal blood vessels. Most characteristically, 5HT-IR nerve fibers invaded the lamina propria of mucosa where they underlay the crypt epithelium. In conclusion, the present study showed that 5HT-IR neurons located in the myenteric plexus projected fibers widely in the rat GI tract. The localization of fibers in the lamina propria of mucosa implies that this neuron may exert an important role in the epithelial function of the GI tract.

Painful vein overdistension in migraine patients: no relationship with serotoninergic parameters.

Overdistension of the hand-forearm veins after a period of ischaemia-induced stasis causes local pain in a high percentage of migraineurs, but never in healthy subjects. To investigate the mechanism of such pain, we compared 5-hydroxytryptamine (5HT) whole blood levels and hand vein 5HT reactivity of migraine subjects who did experience pain during venous overdistension to those who did not. No differences were found in whole blood 5HT levels or in the venoconstrictor activity of 5HT between subjects experiencing pain and those who did not. No correlation was found between whole blood 5HT levels and the degree of 5HT-induced venoconstriction. Our results suggest that, if platelets are considered as a model of central antinociceptive 5HT neurons, pain appearance is not due to reduced 5HT at a central level and, therefore, to increased perception of peripheral nociceptive stimuli. Moreover, the similar 5HT venoconstrictive effect (indirect marker of venous tone and, therefore, of venous distensibility) seems to indicate that a mechanical factor is not involved in pain appearance during the HAVD test.

1911 Distribution of c-fos expressing cells in the trigeminal nucleus caudalis following infraorbital nerve transection in the rat

As one of the main serotonergic (5HT) projections to the forebrain, the dorsal raphe nucleus (DRN) has been implicated in disorders of anxiety and depression. Although the nucleus contains the densest population of 5HT neurons in the brain, at least 50% of cells within this structure are non-serotonergic, including a large population of nitric oxide synthase (NOS) containing neurons. The DRN has a unique topographical efferent organization and can also be divided into sub-regions based on rostro-caudal and medio-lateral dimensions. NOS is co-localized with 5HT in the midline DRN but NOS-positive cells in the lateral wing (LW) of the nucleus do not express 5HT. Interestingly, the NOS LW neuronal population is immediately rostral to and in line with the cholinergic lateral dorsal tegmental nucleus (LDT). We used immunohistochemical methods to investigate the potential serotonergic regulation of NOS LW neurons and also the association of this cell grouping to the LDT. Our results indicate that >75% of NOS LW neurons express the inhibitory 5HT1A receptor and are cholinergic (>90%). The findings suggest this assembly of cells is a rostral extension of the LDT, one that it is subject to regulation by 5HT release. As such the present study suggests a link between 5HT signaling, activation of cholinergic/NOS neurons, and the stress response including the pathophysiology underlying anxiety and depression.

Serotonin and alcohol-related brain damage.

Preliminary results from the immunohistochemical examination of the brainstems of chronic alcoholics, suggest that alcohol may have a role in damage to the principal serotonergic (5HT) nuclei. This view is reinforced by evidence from previous animal experiments which demonstrated a reduction in 5HT neurons in the brains of alcohol-preferring rats and selective neurotoxicity to 5HT neurons following 5,6-dihydroxytryptamine-induced increased ethanol intake. It is speculated that, like other neurotoxins, alcohol or its metabolites cause degeneration of 5HT axons and axon terminals. It is possible that if axonal damage is sufficiently severe and chronic, the eventual consequence is cell death. This could be due to insufficient opportunity for repair and regrowth under repeated and sustained insults of high alcohol consumption.

Identification and characterization of antidepressant-sensitive serotonin transporter proteins using site-specific antibodies

Serotonin (5HT) transporters (SERTs) are responsible for clearance of synaptic and plasma 5HT and are molecular targets for multiple therapeutic and addictive compounds. Recently brain and peripheral SERT cDNAs have been cloned and characterized functionally in transfected cells. Antipeptide (S365) and anti-fusion protein (CT-2) antibodies, directed at epitopes poorly conserved among other Na+/Cl- cotransporters, have been prepared to facilitate the identification and characterization of SERT proteins in native and transfected cells. Immunoprecipitations and immunoblots of rat/human SERT-transfected HeLa cells reveal specific SERT-immunoreactive glycoproteins absent from extracts of vector-transfected cells and absent when incubations were conducted using peptide- or fusion protein-absorbed antibody. In SDS-PAGE of membranes prepared from rat midbrain and cortex, SERTs migrate as single 76 kDa polypeptides with a relative abundance consistent with the known distribution of 5HT neurons and axonal projections. SERT-immunoreactive proteins are also detectable in platelet and pulmonary membranes, sites of peripheral 5HT uptake, but not in liver. Our studies also indicate that brain and platelet SERTs are formed from identical polypeptides differing significantly in their extent of N-linked glycosylation. Immunocytochemistry performed on rat brain sections with CT-2 antibody revealed SERT expression associated with brainstem raphe nuclei in a pattern virtually identical to that obtained by labeling adjacent sections with 5HT antisera. SERT-immunoreactive fibers were found to be widely distributed throughout the rodent brain, with highest density in forebrain regions known to receive a dense serotonergic innervation. In a similar manner, CT-2 antibody also detects endogenous expression of human SERT proteins, providing an opportunity for future studies on the modulation of transporter protein expression in neurologic and psychiatric disorders.

Monoaminergic Depletion and Changes in Aggressive Behavior in Cats and Rats

The involvement of various neurotransmitters in aggressive behavior has been studied intensively for years. It is known that various neurotransmitter systems remain in anatomical and functional interactions and it seems that the changes in their dynamic balance might play an important role in the regulation of complex behaviors. The purpose of our experiments was to study the behavioral and biochemical effects of the destruction of noradrenergic (NA) system in respect to various types of aggression in two different species. In both, cats and rats the experimental paradigms were designed as close to the natural circumstances as it was possible in the laboratory, i.e. predatory behavior and predatory competition for cats, mouse-killing and intruder-resident with computerized ethological analysis for rats. The first series of tests allowed to describe the behavioral profile of all animals. Then submissive cats and rats were treated with selective noradrenergic neurotoxin DSP-4 preceded by zimelidine to protect 5HT neurons. After the completion of the experiments, concentration of NA, 5HT and DA (in case of rats also their metabolites) was measured in brain structures associated with emotional behavior. It has been found that DSP-4 treatment did not affect prey killing in either cats or rats. Also well established dominance-submissive order during predatory competition remained unchanged, except the situation when the stressful stimuli were presented to the pair of cats. In rats, marked decrease of defensive episodes and increase of offense during social interactions, were observed. Simultaneously it was found that DSP-4 treated rats explored more in stressogenic highly illuminated area than controls. Three possible hypotheses are discussed: 1. increase of aggression 2. fear reduction 3. inadequate responsiveness to environmental factors. Biochemical analysis showed significant reduction of NA and some changes in 5HT and DA, which we consider as an effect secondary to NA depletion. In the neurochemical perspective the results obtained can be interpreted in terms of altered NA, 5HT and DA balance that reflects functional interactions within monoaminergic systems.

Host Serotonin Axons Innervate Intrastriatal Ventral Mesencephalic Grafts After Implantation in Newborn Rats

This study investigated the potential of immature and adult serotonin (5-HT) neurons for axonal growth into intrastriatal grafts of ventral mesencephalic tissue. Implantation of dissociated fetal (embryonic days 14-15) ventral mesencephalic tissue was carried out in immature [postnatal days (P) 5-14] and adult rat neostriatum. The brains were processed 2-6 months later for dopamine and 5-HT immunocytochemistry. A few grafts implanted into adult and P7 recipients contained small numbers of cotransplanted 5-HT cell bodies. These also displayed a rich network of 5-HT axons, even in adult rats prelesioned with 5,7-dihydroxytryptamine, indicating the graft origin of these axons. All other grafts were totally devoid of 5-HT cell bodies. After implantation in adults, such grafts contained rare 5-HT axons. In contrast, in P5-P7 recipients, they displayed many 5-HT fibres, which were uniformly distributed. Such was no longer the case after implantation in P14 recipients, which showed minimal 5-HT innervation, as in adult recipients. Processing of naïve rat brain at different ages for 5-HT immunocytochemistry showed that 5-HT axons were still clearly less numerous in the neostriatum at P21 than in adults, whereas in the substantia nigra the 5-HT innervation developed more rapidly and was comparable, at P21, to that of adults. It was concluded that 5-HT axons are able to grow into ventral mesencephalic grafts, but mainly at the fetal stage and with decreasing capacity after birth.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical responses and synaptic connections of giant serotonin-immunoreactive neurons in crayfish olfactory and accessory lobes.

Five pairs of identified 5HT-IR cells in the deutocerebrum of the crayfish Cherax are known to have their synaptic endings in the accessory and olfactory lobes. Two of these cells, one on each side of the brain, are significantly larger than the others. Dye fills of these "giant" cells reveal each to be an interneuron with its branches confined to, but distributed throughout, the olfactory and accessory lobes on the side of the brain ipsilateral to its cell body and with no branches to the contralateral side. Intracellular recordings from the giant cells were made while stimulating the olfactory afferents and tracts within the brain in an attempt to discover the inputs and outputs to the cells. Electrical stimulation of chemoreceptor sensilla on the outer branch of the antennule does not excite the giant 5HT neurons. Focal extracellular electrical stimulation of the olfactory globular tract containing the axons of projection neurons from the olfactory and accessory lobes produces excitatory synaptic potentials and action potentials in the giant cells. Focal extracellular electrical stimulation of the deutocerebral commissure, the axons of which terminate in the glomeruli of the accessory lobes, also results in excitation of the giant cells. We conclude that the input to the giant cells is via axons in the deutocerebral commissure and collaterals from the projection neurons, ending in the glomeruli of the accessory lobes. The output of the giant cells is to the olfactory lobes, where it may serve to modulate olfactory signals.

Effect of reserpine on 5-hydroxytryptophan (5HTP)-immunoreactive neurons in the rat brain.

By immunohistochemistry of rat brain in conjunction with a specific antibody against 5-hydroxytryptophan (5HTP), we examined immunoreactivity to 5HTP in neurons, from which 5-hydroxytryptamine (5HT; serotonin) was depleted by reserpine treatment. The distribution patterns of 5HTP-positive neurons overlapped with those of 5HT neurons. Treatment with reserpine (5 mg/kg, 90 min before death) caused a complete suppression of 5HT-positive staining, but 5HTP-immunostaining remained in perikarya of the nuclei raphe dorsalis, centralis superior and obscurus. Treatment with reserpine (25 mg/kg, 90 min before death) suppressed the 5HTP-immunoreaction in certain perikarya (e.g. of the nucleus raphe dorsalis) and fibres; however, 5HTP-immunostaining remained in perikarya of the nuclei centralis superior and raphe obscurus. This suggests that these neurons synthesize more 5HTP by a process which appears to be stimulated by reserpine.

5HT drugs in animal models of anxiety.

It has been widely accepted that 5HT neurones promote anxiety, in humans as well as in animal models. This could be termed the "classic" hypothesis and it has led to a determined search for drugs which reduce 5HT function, especially agents which have selective actions at 5HT receptor subtypes. However, these novel agents tend to have weak and/or variable effects in animal models and more detailed examination of their actions suggests that not all findings are accounted for by the classic hypothesis. There appear to be circumstances in which increased 5HT activity can reduce anxious behaviour. There is increasing evidence for multiple anxiety mechanisms, which may be able to explain differential patterns of drug effects within and between models. Animal models of anxiety may also detect non-anxiety factors: effects on cognition or on impulsivity could be reflected in some models. This could be important in the light of recent evidence that 5HT-selective reuptake inhibitors are effective in impulsivity disorders. The classic hypothesis of 5HT function in anxiety may be only one part of an increasingly complex story. Unravelling the rest of this story is likely to lead to new insights in our understanding of anxiety and related disorders.

Synaptic loss following removal of serotoninergic fibers in newly hatched and adult chickens.

Neurotransmitters such as serotonin (5HT) may have nontransmitter, trophic-like functions in the developing and adult nervous system. In order to examine this possibility in the avian spinal cord, we have quantified synapse numbers on spinal neurons following treatment with drugs that result in the destruction of 5HT positive axons. Either p-chlorophenylalanine or reserpine was injected into newly hatched or adult chickens. Following treatment for 7 days the density of nonserotoninergic synapses was considerably decreased in the targets of 5HT fibers. By contrast, neither change was observed in the dendritic structures of spinal motoneurons or in the distribution of substance P and enkephalin positive fibers. These data suggest that 5HT may play an important role in the normal increase and maintenance of synapses in developing and adult animals. A lesion of 5HT neurons may not only alter neurochemistry but also alter the general synaptic structures of the brain. While 5HT containing fibers were depleted in a dose-dependent fashion we cannot rule out the possibility that other neurotransmitter systems were depleted at higher dose of PCPA and reserpine.

Colocalization of progestin receptors with serotonin in raphe neurons of macaque.

Progesterone stimulates prolactin secretion in estrogen-primed women and monkeys. We hypothesize that this effect is neurally mediated since pituitary lactotropes do not contain progestin receptors (PR). In rodents, progesterone enhances hypothalamic serotonin (5HT) content, and both progesterone and 5HT stimulate prolactin and LH secretion. However, it was not known whether progesterone acts directly on 5HT neurons or through other neurons. Using a double immunocytochemical procedure, we show that 5HT neurons in macaque contain PR and thus are a progestin target system. Midbrain tissue blocks were obtained from two female monkeys and immersion-fixed prior to freezing and sectioning. PR was detected with a monoclonal antibody against human PR (B39) bridged to horseradish peroxidase and developed in diaminobenzidine. PR immunoreactivity appeared as a brown reaction product which localized in the nuclei of individual neurons. 5HT was detected with an antiserum generated against a conjugate of 5HT and BSA bridged to alkaline phosphatase. 5HT immunoreactivity appeared as a blue reaction product in the cytoplasm and axons of the pontine raphe nucleus. Neurons containing both nuclear reaction product for PR and cytoplasmic reaction product for 5HT were observed in both the dorsal and ventral aspects of the midbrain raphe nucleus as well as the raphe magnus. In summary, progesterone can have a direct action on 5HT neuronal function and thereby influence those endocrine and affective systems under serotonergic control.

Effects of the neurotoxin ethylcholine mustard aziridinium in rat brain reaggregate cultures

The toxicity was studied of ethylcholine mustard aziridinium (ECMA) in rat brain reaggregate cultures. The objective was to define optimum conditions for selective effects on cholinergic neurones. Single treatments with 12.5–50 μ m-ECMA caused approximately 35% loss of choline acetyltransferase (ChAT) activity in 2 hr, increasing to 70–80% in 72–120 hr. The 2-hr, but not the longer-term loss of activity was prevented by the choline transport blocker hemicholinium-3 (40 μ m). Significant loss of ChAT activity could not be obtained with less than 12.5 μ m-ECMA. Approximately 55% irreversible inhibition of muscarinic receptor binding also occurred in 2 hr. However, after 12.5 μ m-ECMA, binding recovered to control values within 48 hr. These persisted throughout the longer-term more extensive loss of ChAT activity, which suggests that receptor recovery localized to cells other than cholinergic neurones. After 25–50 μ m-ECMA, muscarinic receptor binding did not recover, which suggests more widespread cytotoxicity destroying cells other than the cholinergic neurones. More pronounced leakage of lactate dehydrogenase and reduced reaggregate concentrations of total and neurofilament protein were consistent with more generalized cytotoxicity after 25 or 50 μ m-ECMA. Examination of ECMA treated reaggregates or cerebellar monolayer cultures by light microscopy confirmed this. Concentrations of 12.5 μ m-ECMA therefore represent the optimum for achieving selective toxic effects on cholinergic neurones in the cultures. After ECMA, reaggregate concentrations of 5-hydroxyindole acetic acid were markedly increased (100–300%), which suggests increased activity of 5HT neurones. This demonstrates that reaggregate cultures might be used to study trans-synaptic neurochemical sequelae of brain cholinergic neurone loss.

Developmental alteration of serotonin neurons in the raphe nucleus of rats with methylazoxymethanol-induced microcephaly.

Prenatal exposure of pregnant rats to methylazoxymethanol acetate (MAM), an anti-mitotic agent, on day 15 of gestation induces severe microcephaly in the offspring. The present study first investigated a developmental alteration of serotonin (5HT) neurons immunohistochemically in the dorsal and median raphe nuclei in serial sections in both control and microcephalic rats (MAM-rats) at 35 days of age. 5HT-immunoreactive neurons in the MAM-rats were reduced in number and irregularly distributed in the dorsal and median raphe nuclei compared with those in the control. The dendrites of neurons in these nuclei in the MAM-rats were very short and twisted. A follow-up observation on the development of the cerebral cortex at 5, 9 and 28 days of age was performed using Nissl-stained preparations, which revealed a disorganized cell arrangement in the cerebral cortex of the MAM-rats at the very early postnatal period. Furthermore, the distribution of 5HT-immunoreactive fibers into the cerebral cortex was also examined using brains of 28 days of age. In MAM-rats of this age, abnormally tortuous 5HT-immunoreactive fibers were observed in the cerebral cortex. 5HT neurons in the raphe nuclei are known to project their ascending axons widely into the entire cortical area during the 1st postnatal week. Thus, the association of disorganized cortical cell arrangement and the hyperdense and tortuous distribution of 5HT-immunoreactive fibers in the cerebral cortex support the idea of target-dependent secondary degeneration of 5HT neurons in the dorsal and median raphe nuclei of the MAM-rats.

Immunohistochemical Examination of Developmental Brain Defects*

AbstractRecent advances in immunohistochemistry have revealed the precise distribution of various neurotransmitter systems, their projections and ultrastructure in the brain. Based on these data, the structure and function of specific neurons or a group of neurons in the brain can be understood in terms of the dynamics of the neurotransmitters they utilize. This strategy of neuroscience may be utilized to explore higher brain functions such as learning, memory, cognition and sleep. Prenatal exposure of pregnant rats to methylazoxymethanol acetate (MAM) on day 15 of gestation produces offspring with severe microcephaly (MAM‐rats). These MAM‐rats show various behavioral abnormalities in learning, memory and cognition as well as hyperactivity and reduction of paradoxical sleep. Developmental abnormalities of serotonin (5HT) fibers in the cerebral cortex and 5HT neurons in raphe nuclei are examined. The cell deficits of cortical target neurons and irregularly arranged cortical layers were observed. Developmental abnormalities of 5HT neurons are discussed in terms of target dependent secondary degeneration. Vasoactive intestinal polypeptide (VIP) has an important role in behavioral modification. VIP is suggested to have a functional correlation with 5HT in the brain. The reduction of VIP neurons and hypo‐aggregation of their axonal boutons were observed in the cerebral cortex and hippocampus of infant MAM‐rats. However, in adult MAM‐rats, VIP axonal boutons showed layer‐dependent hyper‐ or hypo‐aggregation compared with the age‐matched control. The difference in the number of VIP neurons became small between the controls and MAM‐rats. These immunohistochemical observations of brain defects have an important implication for understanding the abnormal behavior of MAM‐rats.

Characterization of opioid receptor-mediated regulation of incertohypothalamic dopamine neurons: lack of evidence for a role of 5-hydroxytryptaminergic neurons in mediating the stimulatory effects of morphine

The purpose of the present study was to characterize opioid receptor-mediated regulation of incertohypothalamic dopaminergic (DA) neurons in the rat brain by examining the acute effects of selective μ or κ opioid receptor agonists and antagonists on concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) in the medial zona incerta (MZI) and the dorsomedial hypothalamic nucleus (DMN) which contain cell bodies and terminals, respectively, of these neurons. Morphine caused a dose- and time-related increase in concentrations of DOPAC in MZI and DMN; this stimulatory effect was blocked by the μ opioid receptor antagonist naltrexone. In contrast, activation or blockade of κ opioid receptors following administration of U-50,488 or nor-binaltorphimine, respectively, had no effect on DOPAC concentrations in either the MZI or DMN. The basal activity of incertohypothalamic DA neurons and their response to morphine was similar in male and female rats. Morphine also increased the concentrations of 5-hydroxyindoleacetic acid in MZI and DMN, indicating that morphine increases the activity of 5-hydroxytryptamine (5HT) neurons projecting to these regions. This might suggest that morphine-induced activation of incertohypothalamic DA neurons is mediated by 5HT neurons, but 5,7-dihydroxytryptamine-induced lesions of 5HT neurons did not alter the ability of morphine to increase DOPAC concentrations in MZI and DMN. These results indicate that the stimulatory effects of μ opioid receptor activation on incertohypothalamic DA neurons is not dependent upon the presence of 5HT neurons.

The serotoninergic system of the brain of the lamprey, Lampetra fluviatilis: an evolutionary perspective

The distribution of serotonin(5HT)-immunoreactive cell bodies, nerve fibers and terminals was investigated by light microscopy in the lamprey Lampetra fluviatilis. Twenty-three distinct groups of 5HT neuronal somata were identified from diencephalic to rhombencephalic levels in the brain. The diencephalon contained a subependymal population of immunoreactive cells in contact with the cerebrospinal fluid (CSF), which could be subdivided into five separate groups situated in the hypothalamus and ventral thalamus; five additional groups of immunoreactive diencephalic neurons, situated in the dorsal thalamus and thalamo-pretectum, which were not in contact with the CSF, were also identified. In the midbrain, in addition to a few labelled neurons in the optic tectum, two structures containing immunoreactive cells were identified in the tegmentum mesencephali. None of these 5HT cells corresponded to the retinopetal neurons which are situated in the same region. A very large number of 5HT neurons were observed in the hindbrain which could be divided into seven groups in the isthmus rhombencephali and a further three in the rhombencephalon proper. Immunoreactive fibers and terminals were widely distributed throughout the neuraxis. In the telencephalon two 5HT fibers assemblies, lateral and medial, could be identified which terminated in both pallial and subpallial structures. The richest serotoninergic innervation in the telencephalon was found in the lateral portion of the primordium hippocampi and the medial part of the corpus striatum. In the diencephalon, the distribution of immunoreactive fibers and terminals was heterogeneous, being most pronounced in the lateral hypothalamic area and in the infundibulum. The densest arborization of fibers in the mesencephalon was found in the stratum fibrosum et cellulare externum of the optic tectum, a major site of retinal projection, and in the nucleus interpeduncularis mesencephali as well as in the oculomotor nuclei. The rhombencephalon is richly endowed with serotoninergic fibers and terminals, many labelled arborizations being found in the nuclei isthmi rhombencephali and around the nucleus motorius nervi trigemini. Comparative analysis of the serotoninergic systems of petromyzontiforms and gnathostomes indicates that the evolution of this system involves a progressive elimination of the rostral immunoreactive cells and an increasing complexity of the caudal population of serotoninergic neurons.

Aggression and suicide attempts: preliminary data

The similarities between blood platelets and serotonin (5HT) neurons offer a reliable tool of exploring 5HT system. The aim of our study was to evaluate platelet [ 3H]imipramine binding in suicide attempters, as compared with depressed patients and healthy controls. In addition, we measured aggressive features in the 3 groups, by a standardized rating scale, the Inventory for assessing different kinds of ostility (QTA). The results showed a significant decrease in the maximum binding capacity (Bmax) of 3H-imipramine binding to platelet membranes in suicide attempters, who also exhibited higher total and single item scores at QTA than healthy controls or depressed patients. Both biological and psychological findings are suggestive of an aggression dysregulation in suicide attempters.

Effects of Ethanol and Low-Carbohydrate Diet on Contents of Noradrenalin, Dopamine, Serotonin and their Metabolites in Rat Brain.

Effects of ethanol consumption and intake of low-carbohydrate (low-CHO) diet on noradrenaline (NA), dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), serotonin (5HT) and its metabolite, 5-hydroxyindoleacetic acid (5HIAA) contents in six brain regions of rats were investigated. 1) Change of DA neuron Ethanol-containing control diet (hypercaloric ethanol diet) did not affect DA content in any area of brain, but decreased HVA in cortex and hypothalamus and increased DOPAC and HVA in midbrain. Low-CHO diet increased DA content in striatum, DOPAC and HVA in midbrain, but decreased DOPAC in hippocampus and hypothalamus, and HVA in cortex, pons and medulla, hippocampus and hypothalamus. Ethanol-containing low-CHO diet (isocaloric ethanol diet) increased DA level in striatum, DOPAC and HVA in midbrain, but decreased HVA in cortex, hippocampus, striatum and hypothalamus. These results suggest that i) hypercaloric ethanol diet has an opposite effect to carbohydrate on DA metabolism: hypercaloric ethanol diet and lowered carbohydrate intake per se enhance DA metabolism in midbrain, whereas inhibit it in cortex and hypothalamus, ii) lowered carbohydrate intake also declines DA metabolism in pons and medulla and hippocampus, whereas enhances DA synthesis in striatum, iii) the combined effect of ethanol and carbohydrate intake on DA metabolism is inhibited each other in the rats of isocaloric ethanol diet feeding, and this diet decreased DA metabolism in striatum. 2) Change of 5HT neuron Hypercaloric ethanol diet did not affect the contents of 5HT and 5HIAA in any region of brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between Norepinephrine and Serotonin in the Neuroendocrine Control of Growth Hormone Release in the Rat*

Both alpha 2-adrenergic (alpha 2) and serotonergic (5HT) neurons are associated with stimulation of GH secretion via GRH release. The object of this study was to determine whether the 5HT system is involved in the stimulation of GH secretion by alpha 2-receptor agonists. There are two parts of this study. In the first, the relationship between alpha 2-5HT systems were analyzed by determining if alpha 2-stimulated GH release is mediated by 5HT. In this model, systemically administered alpha 2-agonists [clonidine (CLON) or UK14,304] were tested against 5HT antagonists (meterogoline or cyproheptadine) or 5HT synthesis inhibitors (p-chlorophenylalanine methylester hydrochloride). In the second, sites of 5HT-GRH interaction were determined by testing the response to CLON after 5HT neurotoxin [5,7-dihydroxytryptamine (5,7-DHT)] microinjection at specific hypothalamic nuclei. In both experiments sequential blood samples were withdrawn from silastic jugular cannulas in unanesthetized, freely moving animals. Metergoline (0.045 and 0.135 mg/kg, iv) and cyproheptadine (0.969 micrograms/kg, iv) suppressed, in a dose-dependent manner, the CLON (33 or 66 micrograms/kg, iv)-induced GH surge that was detected 15-30 min after injection in control animals. Both cyproheptadine (0.969 micrograms/kg, iv) and p-chlorophenylalanine (300 mg/kg, ip) effectively suppressed the UK14,304 (220 micrograms/kg, iv)-induced GH surge that occurred 15-30 min after injection in control animals. These data suggest that an intact 5HT system is required for alpha 2-stimulated GH release. 5,7-DHT neurotoxin microinjected into the midline arcuate nucleus (6 micrograms/mg,iv) or bilaterally into the ventromedial nucleus or perifornical area (4 micrograms/0.2 microliter) 5 days previously suppressed the CLON (30 micrograms/kg)-induced GH surge only in animals with arcurate nucleus lesions. To determine if the suppression was mediated by inhibition of GH-releasing hormone (GRH) or stimulation of somatostatin (SRIF), an additional experiment was conducted including 5,7-DHT arcuate nucleus-lesioned animals injected with anti-SRIF. Inasmuch as anti-SRIF failed to reverse the 5,7-DHT suppression of GH secretion, the results of this experiment suggest that GRH mediates NE-5HT-induced GH secretion. In conclusion, these data suggest that alpha 2 activation of GH secretion requires intact serotonergic terminals in the arcuate nucleus and most likely involves GRH rather than SRIF, release.