Time course of changes in serotonin and noradrenaline in rat brain after predictable or unpredictable shock

The effects of predictable and unpredictable shock on concentrations of serotonin (5-hydroxytryptamine, 5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan (TP) and noradrenaline (NA) have been studied in 7 regions of rat brain. Two separate experiments have been carried out determining these substances both at 30 min and 2 h after the stress session. Unpredictable shock depleted NA levels in all brain regions except the striatum. However, at 2 h poststress NA in these regions increased significantly in comparison with both controls and predictably shocked rats. Predictable shock also decreased NA in locus coeruleus, brainstem and hypothalamus, which was not observed 2 h later. Both predictable and unpredictable shock decreased 5-HT in brainstem and hypothalamus. At 2 h poststress, 5-HT levels in these regions were still decreased in predictably shocked rats, but had attained control values in unpredictably shocked rats. 5-HT metabolism expressed as the 5-HIAA/5-HT ratio, was significantly increased 30 min after predictable shock in all regions except the locus coeruleus and hippocampus. Unpredictable shock produced a much more marked increase in 5-HIAA/5-HT ratio. At 2 h poststress 5-HT metabolism returned to control values in most of the brain regions of predictably shocked animals, but it remained high after unpredictable shock. The activation of serotonergic metabolism following each type of shock is different according to the nucleus in which the 5-HT nerve endings originate. Only slight increases in tryptophan were observed after both types of shock. Our results suggest that unpredictable shock is perceived as a more anxiogenic situation and that under this condition both 5-HT and NA levels are more effectively normalized with time.     

Antidepressant-like effects of liquiritin and isoliquiritin from Glycyrrhiza uralensis in the forced swimming test and tail suspension test in mice

Two classic animal behavior despair tests--the Forced Swimming Test (FST) and the Tail Suspension Test (TST) were used to evaluate the antidepressant activity of liquiritin and isoliquiritin from Glycyrrhiza uralensis in mice. It was observed that both liquiritin and isoliquiritin at doses of 10, 20 and 40 mg/kg significantly reduced the immobility time in the FST and TST in mice 30 min after treatment. Measurement of locomotor activity indicated that liquiritin and isoliquiritin had no central nervous system (CNS)-stimulating effects. The main monoamine neurotransmitters and their metabolites in mouse brain regions were also simultaneously determined by HPLC-ECD. It was found that these two compounds significantly increased the concentrations of the main neurotransmitters 5-HT and NE in the hippocampus, hypothalamus and cortex. Liquiritin and isoliquiritin also significantly reduced the ratio of 5-HIAA/5-HT in the hippocampus, hypothalamus and cortex, slowing down 5-HT metabolism compared with mice treated with vehicle+stress. In conclusion, liquiritin and isoliquiritin produced significant antidepressant-like effects, and their mechanism of action may be due to increased 5-HT and NE in the mouse hippocampus, hypothalamus and cortex.     

Indoleamine and catecholamine concentrations in the mid-term human fetal brain

Because of the likelihood that androgen-induced sex specific brain differentiation is mediated by various neurotransmitters, their concentrations were measured in the mid-term human fetal hypothalamus, cortex and cerebrospinal fluid (CSF). Tissue was collected from 32 hysterotomy specimens aged from 10 to 23 weeks, immediately frozen in liquid nitrogen, and stored at -20 degrees C. 5-Hydroxytryptamine (5-HT), 5-hydroxy indole acetic acid (5-HIAA), norepinephrine (NE) and dopamine (DA) levels were measured by a fluorometric assay. Cord serum testosterone levels were measured by radioimmunoassay. In the male fetuses, hypothalamic concentrations of 5-HT, 5-HIAA and NE were all significantly increased in comparison to those in the cortex. Because the number of female fetuses was small, only the 5-HIAA levels were seen to be significantly higher in the hypothalamus than in the cortex. In the CSF from fetuses of both sexes, the DA levels were greatly raised. Concentrations of NE were significantly higher in male fetuses aged from 14-16 weeks, a time when plasma testosterone levels are also elevated. It is hypothesized that the raised plasma testosterone and hypothalamic NE concentrations are inter-related.     

Profile of NE, DA and 5-HT activity shifts in medial hypothalamus perfused by 2-DG and insulin in the sated or fasted rat

This study was carried out in the unrestrained rat to determine the nature of the in vivo profile of monoamine neurotransmitters within the medial hypothalamus in response to the presence of a glucoprivic or metabolic challenge to neurons within this region. In these experiments, insulin or 2-deoxy-D-glucose (2-DG) was applied locally to the paraventricular nucleus (PVN), dorsomedial nucleus (DMN) and ventromedial hypothalamus (VMH). In each of 11 Sprague-Dawley rats, a guide cannula was implanted stereotaxically to rest just above these structures. Upon recovery, a concentric push-pull cannula system was used to perfuse an artificial CSF within a medial hypothalamic site. The CSF was perfused at a rate of 20 microliters/min with a 5.0 min interval intervening between the collection of each 100 microliters sample. After the rat was fasted for 20-22 hr, either 10 micrograms/microliters 2-DG or 4.0 mU/microliters of insulin was incorporated into the control CSF medium and perfused at the same locus. The aliquots of hypothalamic perfusate were assayed by high performance liquid chromatography with electrochemical detection (HPLC-EC) for the respective concentration in pg/microliter of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and each of their major metabolic products. When the rat was sated, 2-DG enhanced significantly the mean efflux of NE from the medial hypothalamus in comparison to control CSF values. However, under the fasted condition, 2-DG augmented the turnover of both the catecholamine and 5-HT as reflected by elevated levels of MHPG and 5-HIAA, respectively. On the other hand, insulin perfused within the same medial hypothalamic sites evoked a significant increase in the synthesis and release of DA from the sated rat, but did not alter its turnover. Following the interval of fast, insulin produced no immediate alteration in transmitter activity; however, in the interval following insulin's perfusion, DA and 5-HT turnover were enhanced while the efflux of 5-HT was suppressed. An analysis of the proportional values of the levels of the amines to each other revealed marked shifts in the relationships between the catechol- and indoleamine transmitters following local perfusion with both 2-DG and insulin. Overall, NE synthesis and turnover exceeded that of 5-HT following 2-DG, whereas DA predominated over NE and 5-HT during insulin's perfusion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Circadian patterns of serotonin (5-HT) accumulation after pargyline treatment in the rat hypothalamus during development

The purpose of this study was to determine if developmental changes in serotonin (5-HT) synthesis occur during maturation of the 5-HT circadian rhythm in the rat hypothalamus of 10- to 35-day-old rats. Pargyline (75 mg/kg, s.c.), a monoamine oxidase (MAO) inhibitor, was administered 30 min prior to decapitation. Hypothalamic 5-HT concentrations after pargyline treatment were measured at six time points over a 24-hr interval in male and female rat pups at 10, 20, 30 and 35 days of age. Daily fluctuations in hypothalamic 5-HT accumulation were detectable as early as 10 days of age in rats of both sexes. Since the influence of MAO on hypothalamic 5-HT concentrations was eliminated by pargyline treatment, the findings suggest that changes in tryptophan hydroxylase activity contribute significantly to daily and age-related patterns of 5-HT accumulation in the rat hypothalamus during development. Circadian rhythms in hypothalamic norepinephrine (NE) and dopamine (DA) also occurred during development; however, sex differences were not detected for these biogenic amines. Since catecholamine catabolism is not exclusively mediated by MAO, our findings are insufficient to conclude whether or not sex differences actually exist in patterns of these monoamines.     

Modulatory Effects of Melatonin on Cadmium-Induced Changes in Biogenic Amines in Rat Hypothalamus

This study was undertaken to examine whether cadmium oral exposure modifies biogenic amine concentration at hypothalamic level in adult male rats, and to investigate the possible modulatory effects of melatonin against cadmium-induced changes on these neurotransmitters. For this purpose, rats were exposed to cadmium (25 mg/l of CdCl₂ in the drinking water) with or without melatonin (30 μg/rat/day intraperitoneally) for 30 days. Norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenyl acetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) were quantified by high performance liquid chromatography (HPLC). Oral cadmium administration led to decrease of NE, DA, and 5-HT content and DA turnover within the three hypothalamic regions examined, and therefore an inhibition of 5-HT turnover at posterior hypothalamus. Sensitivity to melatonin was specific to the hypothalamic region evaluated. Thus, the anterior hypothalamus was not nearly sensitive to exogenously administered melatonin, whereas the neurohormone decreased the content of these amines in the mediobasal hypothalamus, and melatonin increased it in the posterior hypothalamic region. Melatonin effectively prevented some cadmium-induced alterations on hypothalamic amine concentration. This is the case of DA in the anterior and posterior hypothalamus, and 5-HT metabolism in the posterior hypothalamic region. In conclusion, the obtained results indicate that melatonin treatment may be effective modulating some neurotoxic effects induced by cadmium exposure, and, more to the point, a possible role of this indolamine as a preventive agent for environmental or occupational cadmium contamination.     

Effects of neonatal rat Borna disease virus (BDV) infection on the postnatal development of the brain monoaminergic systems

Effects of neonatal Borna disease virus infection (BDV) on the postnatal development of brain monoaminergic systems in rats were studied. Tissue content of norepinephrine (NE), dopamine (DA) and its metabolite, 3,4-dihydroxyphenol acetic acid (DOPAC), and serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed by means of HPLC-EC in frontal cortex, cerebellum, hippocampus, hypothalamus and striatum of neonatally BDV-infected and sham-inoculated male Lewis rats of 8, 14, 21, 60 and 90 days of age. Both NE and 5-HT concentrations were significantly affected by neonatal BDV infection. The cortical and cerebellar levels of NE and 5-HT were significantly greater in BDV-infected rats than control animals at postnatal days (PND) 60 and 90. Tissue content of NE in hippocampus was unaffected. In hippocampus, neonatally BDV-infected rats had lower 5-HT levels at PND 8 and significantly elevated levels at PND 21 and onwards. Neither striatal levels of 5-HT nor hypothalamic levels of 5-HT and NE were affected by neonatal BDV infection, suggesting that the monoamine systems in the prenatally maturing brain regions are less sensitive to effects of neonatal viral infection. 5-HIAA/5-HT ratio was not altered in BDV-infected rats indicating no changes in the 5-HT turnover in the brain regions damaged by the virus. Neither DA nor DOPAC/DA ratio was affected by neonatal BDV infection in any of the brain regions examined. The present data demonstrate significant and specific alterations in monoaminergic systems in neonatally BDV-infected rats. This pattern of changes is consistent with the previously reported behavioral abnormalities resulting from neonatal BDV infection.     

Blunted responsiveness of posterior hypothalamic norepinephrine to quinpirole in DOCA/NaCl hypertensive rats

Our previous studies have demonstrated that the specific dopamine D2 receptor agonist, quinpirole (LY171555), has a pressor effect in conscious normotensive rats and that this is accompanied by a centrally mediated increase in sympathetic activity and arginine vasopressin release. This pressor response to quinpirole is blunted in the DOCA/NaCl hypertensive rat. To examine the hypothesis that the responsiveness of the central noradrenergic and serotonergic systems to quinpirole treatment is altered in DOCA/NaCl rats, the norepinephrine (NE), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) contents of hypothalamic and brainstem areas were measured in 4-week DOCA/NaCl hypertensive and H2O control rats 15 minutes after the intravenous administration of quinpirole (1 mg/kg). The results demonstrate that quinpirole selectively reduced (26%) posterior hypothalamic NE content in control rats, but not in DOCA/NaCl hypertensive rats. The NE content in the spinal cord and 5-HIAA content in the pons were greater in DOCA/NaCl rats than in normotensive controls in both saline and quinpirole treated groups. Our data suggest that the specific D2 agonist may effect its central pressor response by stimulating NE release from posterior hypothalamic area, a "pressor" region of hypothalamus, and that this D2 agonist induced pressor mechanism may be blunted in DOCA/NaCl hypertension.     

Influence of forced swimming stress on 5-HT1A receptors and serotonin levels in mouse brain

Several stressful factors are able to modify 5-HT1A receptors; for example, different schemes of forced swimming-induced stress (FS) produce a variety of changes in synthesis as well as in 5-HT1A binding in the brain. In addition, it is known that the concentration of 5-HT in the brain is modified as a consequence of acute stressing. The main purpose of this study was to characterize the influence of 15 min of FS on 5-HT levels and on 5-HT1A receptor density in specific brain areas. Mice stressed 24 h before were sacrificed and their brains processed by means of a quantitative autoradiography technique. The following areas were studied: dorsal raphe nucleus (DRN); median raphe nucleus (MRN); thalamus; hypothalamus; amygdala, and hippocampus. 5-HT and 5-hydroxyindolacetic acid (5-HIAA) concentrations in the brainstem, thalamus-hypothalamus, and hippocampus of stressed (ST) mice were analyzed 24 h after stressing by high performance liquid chromatography (HPLC) with fluorometric detection. All data were compared with corresponding unstressed (UST) controls. A significant decrease in 5-HT1A receptor density in DRN, MRN, and hippocampus, accompanied by an increase in labeling of 5-HT1A receptor in thalamus, hypothalamus, and amygdala was observed in ST animals. FS induced a decrease in the 5-HT concentration in the thalamus-hypothalamus, accompanied by an increase in hippocampus areas without affecting 5-HT concentration in the brainstem. Additionally, 5-HIAA/5-HT ratio in the thalamus-hypothalamus area was increased. This study showed that stress alters both 5-HT concentration and 5-HT1A receptors in a region-specific manner.     

Effects of ketamine on dopamine metabolism during anesthesia in discrete brain regions in mice: comparison with the effects during the recovery and subanesthetic phases

The effects of ketamine on the levels of dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were examined in discrete brain regions in mice. A high dose of ketamine (150 mg/kg, i.p.) did not change DA metabolism in the frontal cortex, nucleus accumbens, striatum and hippocampus, but did decrease it in the brainstem during anesthesia. In contrast, during recovery from the ketamine anesthesia, the high dose increased the level of homovanillic acid (HVA) in all brain regions. A low subanesthetic dose of ketamine (30 mg/kg, i.p.) increased the concentrations of both 3,4-dihydroxyphenylacetic acid (DOPAC) and HVA only in the nucleus accumbens. The DA level was not affected by any ketamine treatment. During ketamine anesthesia, the content of 3-methoxy-4-hydroxy-phenylglycol (MHPG) was decreased in the brainstem, whereas during recovery from anesthesia, the MHPG level was increased in the frontal cortex, nucleus accumbens and brainstem. The NE content was not altered in any region by ketamine treatment. The concentration of 5-hydroxyindoleacetic acid (5-HIAA) was reduced in the frontal cortex, striatum, hippocampus and brainstem during ketamine anesthesia. The 5-HT level was unaltered in all regions except the brainstem where it was reduced. In contrast, after anesthesia, the concentrations of both 5-HT and 5-HIAA were increased in the striatum. During the subanesthetic phase, however, the levels of NE, 5-HT and their metabolites were unchanged. These neurochemical results are consistent with the electrophysiological findings that a high dose of ketamine does not change the basal firing rates of nigrostriatal DA neurons during anesthesia, while low subanesthetic doses significantly increase those of ventral tegmental DA neurons.     

Daily rhythms of serotonin metabolism in the medial hypothalamus of the chicken: effects of pinealectomy and exogenous melatonin

Indoleamine levels in punches of the medial hypothalamus containing the suprachiasmatic nuclei (SCN) of 4-week-old cockerels were determined by HPLC-EC. Melatonin levels in punches were determined by radioimmunoassay (RIA). Daily rhythms of serotonin (5-HT) and of its metabolite 5-hydroxy-3-indoleacetic acid (5-HIAA) were observed; levels were higher at midnight than at midday. A daily rhythm with the same phase in punch melatonin content was also observed. Pinealectomy at 1 week after hatching abolished the 5-HIAA and melatonin rhythm in 4-week-old birds but did not abolish the 5-HT rhythm. Injections of melatonin (0.5 mg/kg) increased 5-HT, 5-HIAA and melatonin levels in the hypothalamic punches. These results indicate that circulating melatonin of pineal origin may act to increase 5-HT turnover and/or release in the SCN. They suggest a link between the circadian secretion of pineal melatonin and the regulation of 5-HT projections to the hypothalamus from the raphe nuclei in the brainstem of the chicken. We have previously shown that the rhythmic secretion of melatonin by the pineal is influenced by oscillators in the brain via the superior cervical ganglia. The results reported here indicate that melatonin in turn may regulate brain oscillators, suggesting a neuroendocrine loop within the avian circadian system.     

Analysis of temporal and dose-dependent effects of estrogen on monoamines in brain nuclei

Levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) were measured in hypothalamic and limbic nuclei of ovariectomized rats after various doses of estradiol and at various intervals after estradiol administration. Of 13 areas examined, time- and dose-dependent effects of estrogen on monoamine content were restricted to only a few, discrete areas which concentrate estradiol. Subcutaneous administration of 1-50 micrograms of estradiol benzoate (EB) and measurement of monoamines 24 h later was associated with dose-dependent increases of NE in the medial preoptic nucleus, diagonal band nucleus and periventricular area of the anterior hypothalamus, and increased levels of DA in the periventricular area of the preoptic area. No changes were found in 5-HT levels, but dose-dependent increases in the level of the 5-HT metabolite, 5-hydroxyindole acetic acid (5-HIAA), were measured in the lateral portion of the ventromedial nucleus. Effects of 5 micrograms of EB were evaluated at 1.5, 6, 12 and 45 h after administration. No changes were noted at 1.5 h, but 5-HIAA in the ventromedial nucleus was elevated at 6 and 12 h. NE levels were elevated at 12 and 45 h in the diagonal band and preoptic nuclei and at 45 h in the lateral septum and periventricular area of the hypothalamus. DA levels decreased in the arcuate-median eminence area 45 h after estrogen. Intravenous administration of 10 micrograms of estrogen and measurement of monoamines 1 h later was not associated with altered levels of any monoamine suggesting that the estrogen-dependent changes are consistent with the genomic model for steroid hormone action.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of stress of postnatal development on corticosterone,serotonin and behavioral changes

Stressful events early in life are associated with later psychiatric disorders. We focused on developmental stage and evaluated changes in the corticosterone and serotonergic systems as well as in later anxiety-related behavioral tests. Stressed male Wistar rats were divided into two groups: stressed from postnatal day 11 (PND 11) to 15 and stressed from PND 16 to 20. The rats were exposed to an elevated open platform. Stress increased corticosterone in both experimental groups. In the hypothalamus, amygdala and hippocampus, 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) increased in the rats stressed from PND 11 to 15, and decreased in the rats stressed from PND 16 to 20. In a later behavioral test, rats stressed from PND 11 to 15 traveled shorter distances and tended to spend less time in the center than control rats following restraint stress. There were no significant changes in 5-HT and 5-HIAA in hypothalamus, amygdala and hippocampus after restraint stress in adults. These findings indicate that stress reactions and later effects are different depending on the developmental stage during which the rats were stressed. Stress during the PND 11–15 period may enhance later anxiety-related behaviors without altering 5-HT and 5-HIAA content.     

Comparison of Stress-induced Changes in Noradrenergic and Serotonergic Neurons in the Rat Hippocampus Using Microdialysis

The effects of stress on the serotonergic and noradrenergic projection to the hippocampus were compared in freely moving rats using microdialysis. Stress-induced changes in 5-hydroxytryptamine (5-HT), noradrenaline and their metabolites 5-hydroxyindoleacetic acid (5-HIAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured in the presence of their respective uptake blockers. Local infusion of tetrodotoxin and replacement of Ca²⁺ with Cd²⁺ were used to test dependence on impulse traffic. A 5 min tail pinch or 10 min restraint stress increased 5-HT, 5-HIAA, noradrenaline and DOPAC levels. A subcutaneous saline injection produced an increase in 5-HT and DOPAC but not noradrenaline or 5-HIAA. Although α₂ adrenoceptor agonists and antagonists produced changes in the baseline values of noradrenaline and DOPAC, they had little or no effect on stress-induced changes. Both the abolition of impulse traffic and its enhancement by stress had a greater effect on transmitter than on metabolite levels. Although the responses to stress of the noradrenergic and serotonergic pathway showed many similarities, there was evidence for their activation by separate pathways.     

Changes in cortical and subcortical levels of monoamines and their metabolites following unilateral ventrolateral cortical lesions in the rat

Suction lesions were made in the anterior, posterior or both halves of the right ventrolateral cortex in rats. Six days later, levels of the monoamine neurotransmitters, norepinephrine (NE), dopamine (DA) and serotonin (5-HT), and their metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA), were measured in cortical and subcortical regions of lesioned rats and compared to values in sham-operated animals. NE and 5-HT were decreased in sections of ipsilateral (right) cortex including, and posterior to lesions, while 5-HIAA was increased throughout the ipsilateral cortex. Decreases in monoamines and increases in metabolites and metabolite:monoamine ratios (especially 5-HIAA:5-HT) were found in ipsilateral subcortical structures, including striatum, nucleus accumbens, hippocampus, hypothalamus, midbrain and brainstem, depending on the type of lesion. Subacutely, focal ventrolateral cortical lesions may profoundly alter the levels and utilization rates of monoamine neurotransmitters in widespread regions of the ipsilateral hemisphere.     

Involvement of noradrenergic and 5-hydroxytryptaminergic systems in allylnitrile-induced head twitching

Allylnitrile induces in rats persistent behavioral abnormalities, including head twitching, following a single administration. We studied the role of 5-hydroxytryptamine (5-HT) and noradrenaline (NA) systems in the brain of rats in inducing and maintaining the head twitching. Allynitrile (1.49 mmol/kg) induced 5-HT system activation in all areas of the brain studied 1–4 days after oral administration, and a reduction in the content of NA in the hippocampus, cortex and hypothalamus 1 day after dosing, in the hippocampus, cortex, hypothalamus and midbrain 2 days after dosing, and in the hypothalamus 4 days after dosing. Allylnitrile induced no change in the content of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) or NA 7–28 days after dosing. Pretreatment with 5,7-dihydroxytryptamine (5,7-DHT) suppressed the allylnitrile-induced head twitching, and decreased the contents of 5-HT and 5-HIAA in almost all areas of the brain throughout the observation period, as well as the ratio of 5-HIAA/5-HT in the medulla oblongata plus pons from 1 to 30 days after dosing with allylnitrile. No change in NA was observed in any areas of the brain. Pretreatment withN-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) increased the head twitching induced by allylnitrile, and decreased the content of NA in all areas of the brain throughout the observation period, without any change in the contents of 5-HT or 5-HIAA or in the ratio of 5-HIAA/5-HT. The present results suggest the involvement of 5-HT and NA systems in allylnitrile-induced head twitching.     

Effects of Newcastle disease virus administration to mice on the metabolism of cerebral biogenic amines, plasma corticosterone, and lymphocyte proliferation

Newcastle disease virus (NDV) administration to mice increased concentrations of plasma corticosterone, with a maximal effect at 8 h. This elevation of plasma corticosterone concentrations was not observed in hypophysectomized animals in which the completeness of the hypophysectomy was verified by functional tests. NDV administration consistently increased concentrations of free tryptophan in all brain regions examined (prefrontal cortex, hypothalamus, and brain stem). It also caused an activation of cerebral catecholamine and indoleamine metabolism as determined by measurement of the amines and their catabolites. 3-Methoxy,4-hydroxyphenylethyleneglycol (MHPG), the major catabolite of norepinephrine (NE), homovanillic acid (HVA), a major catabolite of dopamine (DA), and 5-hydroxyindoleacetic acid (5-HIAA), the major catabolite of serotonin (5-HT), were all increased in both hypothalamus and brain stem. Ratios of catabolites to the parent amine, considered to be an index of utilization of the neurotransmitters, were increased for NE, DA, and 5-HT in the hypothalamus and for DA and 5-HT in the brain stem. This pattern of changes resembles that observed following stressors such as footshock or restraint. There were also significant increases of tryptophan, HVA, dihydroxyphenylacetic acid (DOPAC), and 5-HIAA in hypophysectomized relative to sham-operated mice. The NDV treatment also increased thymus weights and markedly decreased the proliferative responses of isolated spleen cells to phytohemagglutinin, concanavalin A, pokeweed mitogen, and Escherichia coli lipopolysaccharide. These changes were not caused by increased circulating corticosterone because they were present at equal magnitude in hypophysectomized mice. Thymosin alpha 1 concentrations in the plasma were not altered by NDV or hypophysectomy. These results indicate that administration of NDV to mice can initiate neurochemical and endocrine responses like those observed during stress and can also cause immunosuppression. They are thus consistent with the hypothesis that a virus can be a stressor.     

GABAergic drugs alter hypothalamic serotonin release and lordosis in estrogen-primed rats

The effects of muscimol, a GABA(A) agonist, and phaclofen, a GABA(B) antagonist, on serotonin (5HT) release in the mediobasal hypothalamus and lordosis behavior were studied in freely moving rats using in vivo microdialysis. Two days after implantation of bilateral guide cannulae directed towards the ventromedial nucleus of the hypothalamus (VMH), ovariectomized rats were primed with estradiol (E(2)). The rats were implanted with microdialysis probes 24 h later. Following a pretest for lordosis, perfusate 5HT was measured at 20-min intervals until the baseline was stable. The rats were treated with 10, 30 or 100 microM muscimol or 30 and 100 microM phaclofen in artificial CSF delivered via reverse dialysis for 40 min. Control animals were continuously perfused with artificial CSF. Behavior was tested 20, 60 and 180 min after introduction of the drug. Decreased hypothalamic 5HT (40-60% of baseline) and marked facilitation of lordosis were present 20 min after administration of either drug. The effects of 10 and 30 microM muscimol and 30 microM phaclofen on both 5HT and lordosis were reversed after 180 min. Reversal of the behavioral and neurochemical effects were not evident in either the 100 microM muscimol or 100 microM phaclofen groups at the time-points tested. Proceptive responses were observed in phaclofen-treated rats but not in rats treated with muscimol. Levels of hypothalamic 5HT and lordosis quotients in control rats did not significantly differ from initial values. These results suggest that GABAergic effects on lordosis may be mediated through an interaction with 5HT in the mediobasal hypothalamus.     

Changes in Pineal Indoleamines in Rats after Single Melatonin Injections: Evidence for a Diurnal Sensitivity to Melatonin

We recently determined that melatonin stimulated serotonin (5-HT) secretion from rat pineal glands by increasing 5-HT release from the pinealocytes (μM melatonin concentrations) and by inhibiting 5-HT uptake in the pineal sympathetic nerve endings (mM melatonin concentrations). The present study investigated whether a single melatonin injection could alter the content of indoleamines in the rat pineal gland, as well as its possible dependence on the daytime of administration. Melatonin (150 μg/kg) was i.p. injected at 8 time points (11.00 h, 14.00 h, 17.00 h, 20.00 h, 23.00 h, 02.00 h, 05.00 h and 08.00 h) to rats kept in 12:12 h light:dark cycle (lights on at 07.00 h). Melatonin injections in the afternoon (17:00 h) and late in the nighttime (02.00 h and 05.00 h) decreased pineal 5-HT content 90 min later. The levels of 5-hydroxyindoleacetic acid (5-HIAA) were also decreased 90 min after the melatonin treatment at 14.00 h, 17.00 h and 02.00 h. The effect of melatonin on 5-HT content was a long-lasting effect (still evident after 180 min) only when injected at 02.00 h, whereas 5-HIAA levels were found to be decreased 180 min after melatonin treatment at 14.00 h and 23.00 h. No changes in these compounds were detected 240 min after melatonin treatment. Moreover, melatonin did not change 5-hydroxytryptophan levels at any of the daytime points studied. By contrast, 90 min after the injection of melatonin at 20.00 h, an increased content of pineal N-acetylserotonin was observed. This effect of melatonin could be mediated through a phase alteration of the pineal N-acetyltransferase activity rhythm by acting on the suprachiasmatic clock, althought a direct melatonin effect on the pineal rhythmic function cannot be excluded. The effects of the hormone on 5-HT and 5-HIAA contents agree with previous findings on the inhibitory effect of pharmacological doses of melatonin on pineal 5-HT uptake, which presumably would result in a decreased intraneuronal content of 5-HT and its acid metabolite. These data point to an acute regulatory action of exogenous melatonin on the pineal melatonin synthesis pathway which seems to be limited to two daytime phases: the afternoon-early evening period and the second half of the night.     

Effects of intracisternal vs. intrahypothalamic 5,7-DHT on feeding elicited by hypothalamic infusion of NE.

A variety of evidence has led to suggestions that brain serotonin (5-HT) and norepinephrine (NE) interact within the medial hypothalamus to control food intake. To test the possibility that chronic decrements in 5-HT might enhance NE-induced feeding, adult male rats were prepared with permanently indwelling cannulae aimed at the paraventricular nucleus (PVN), then received either intracisternal (IC) or PVN injections of the 5-HT neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT) vs. its vehicle, 1% ascorbic acid. Over a 4-week period, IC-5,7-DHT rats showed no signs of enhanced daily feeding or drinking. However, in 40-min intake tests, feeding but not drinking was enhanced by injecting 20 nmol NE into the PVN commencing 2 weeks after neurotoxin treatment. Terminal monoamine assays confirmed that IC-5,7-DHT produced large (80-90%) depletions of brain regional 5-HT. A functional index of 5-HT terminal damage was also implied by the impaired short-term feeding responses IC-5,7-DHT rats showed to the systemic administration of the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) when tested between 3 and 4 weeks after IC treatment. Over a comparable 4-week period, PVN-5,7-DHT rats also showed no tendencies to overeat or overdrink on a daily basis. However, in contrast to IC-5,7-DHT rats, they also showed no differences in their feeding or drinking responses to NE injections into the PVN. This was so despite reliable depletions of 5-HT in the hypothalamus (-28%) and hippocampus (-71%). These results support earlier work showing that neither widespread nor localized hypothalamic damage to brain 5-HT neurons produce chronic overeating. However, the data suggest that phasic enhancements of PVN NE activity may trigger enhanced feeding when there is widespread damage to brain 5-HT neurons, although the PVN does not appear to be the brain site mediating this effect.