Involvement of the GABAA/benzodiazepine chloride ionophore receptor complex in the 5,7-DHT Induced anticonflict effect.

The effects of drugs interacting with the GABAA/benzodiazepine chloride ionophore receptor complex (GABAA/BDZ-RC) on the anticonflict and biochemical effects observed after intracerebroventricular (i.c.v.) administration of 5,7-dihydroxytryptamine (5,7-DHT; 450 micrograms -14 days) were investigated in the rat using a modified Vogel's drinking conflict test. The GABAergic antagonistic drugs bicuculline, picrotoxin and Ro 15-4513 all counteracted the 5,7-DHT induced anxiolytic-like action in doses that did not alter the behavior per se, whereas flumazenil was ineffective in this respect. Also i.c.v. administration of 5-HT antagonized the 5,7-DHT induced anticonflict effect. Furthermore, 5,7-DHT-lesioned animals appeared more sensitive to the anticonflict effects of diazepam than sham-lesioned controls. The 5,7-DHT treatment produced marked depletions of 5-HT in the limbic system (80-90%) and hippocampus (90-95%), and an increase in the 5-HIAA/5-HT quotient in hippocampus. The effects on the levels of noradrenaline were comparatively small. The doses of bicuculline and picrotoxin antagonizing the 5,7-DHT induced anticonflict effect did not uniformly influence 5-HT levels or 5-HIAA/5-HT quotients. It is suggested that the anxiolytic-like effect observed in 5,7-DHT-lesioned rats in Vogel's drinking conflict test involves enhanced transmission at the GABAA/BDZ-RC.     

In vivo regulation of the serotonin-2 receptor in rat brain

Serotonin-2 (5-HT-2) receptors in brain were measured using [3H]ketanserin. We examined the effects of amitriptyline, an antidepressant drug, of electroconvulsive shock (ECS) and of drug-induced alterations in presynaptic 5-HT function on [3H]ketanserin binding to 5-HT-2 receptors in rat brain. The importance of intact 5-HT axons to the up-regulation of 5-HT-2 receptors by ECS was also investigated, and an attempt was made to relate the ECS-induced increase in this receptor to changes in 5-HT presynaptic mechanisms. Twelve days of ECS increased the number of 5-HT-2 receptors in frontal cortex. Neither the IC50 nor the Hill coefficient of 5-HT in competing for [3H]ketanserin binding sites was altered by ECS. Repeated injections of amitriptyline reduced the number of 5-HT-2 receptors in frontal cortex. Reserpine, administered daily for 12 days, caused a significant increase in 5-HT-2 receptors, but neither daily injections of p-chlorophenylalanine (PCPA) nor lesions of 5-HT axons with 5,7-dihydroxytryptamine (5,7-DHT) affected 5-HT-2 receptors. However, regulation of 5-HT-2 receptors by ECS was dependent on intact 5-HT axons since ECS could not increase the number of 5-HT-2 receptors in rats previously lesioned with 5,7-DHT. Repeated ECS, however, does not appear to affect either the high-affinity uptake of [3H]5-HT or [3H]imipramine binding, two presynaptic markers of 5-HT neuronal function. 5-HT-2 receptors appear to be under complex control. ECS or drug treatments such as reserpine or amitriptyline, which affect several monoamine neurotransmission systems including 5-HT, can alter 5-HT-2 receptors. While depleting 5-HT alone (5,7-DHT or PCPA) does not alter [3H]ketanserin binding to 5-HT-2 receptors, intact 5-HT axons are necessary for the adaptive up-regulation of the receptor following ECS.     

Effects of serotonin depletion byp-chlorophenylalanine,p-chloroamphetamine or 5,7-dihydroxytryptamine on central dopaminergic neurons: Focus on tuberoinfundibular dopaminergic neurons and serum prolactin

Three serotonin (5-HT) neurotoxins,p-chlorophenylalanine (PCPA, 125 and 250 mg/kg, i.p.),p-chloroamphetamine (PCA, 10 mg/kg, i.p.) and 5,7-dihydroxytryptamine (5,7-DHT, 200 µg/rat, i.c.v.) were used to examine whether depletion of central 5-HT has an effect on central dopaminergic (DA) neuronal activities or on prolactin (PRL) secretion. Adult ovariectomized Sprague-Dawley rats primed with estrogen (polyestradiol phosphate, 0.1 mg/rat, s.c.) were treated with one of three neurotoxins and then decapitated in the morning after 3–7 days. Blood sample and brain tissues were collected. The acute effect of PCA (from 30 to 180 min) was also determined. The concentrations of 5-HT, DA and their metabolites, 5-hydroxyindoleacetic acid and 3,4-dihydroxyphenylacetic acid, in the median eminence, striatum and nucleus accumbens were determined by HPLC-electrochemical detection. All three toxins significantly depleted central 5-HT stores by 11–20%. Except for PCPA, neither PCA nor 5,7-DHT had any significant effect on basal DA neuronal activities or PRL secretion. PCA also exhibited an acute effect on the release and reuptake of 5-HT and DA. In summary, depletion of central 5-HT stores to a significant extent for 3–7 days did not seem to affect basal DA neuronal activity and PRL secretion.     

Role of angiotensin in body fluid homeostasis of mice: effect of losartan on water and NaCl intakes

It is known that mice injected peripherally with ANG II do not show a drinking response but that cFos immunoreactivity (ir) is induced in brain regions similar to those in rats. We now show in Crl:CD1(ICR) mice that peripheral injection of the ANG II type 1 receptor antagonist losartan was sufficient to prevent this induction of Fos-ir in the subfornical organ (SFO). Injection of ANG II into the lateral cerebral ventricle produced a robust water intake in mice and induced Fos-ir in SFO, as well as in median preoptic (MnPO) and paraventricular (PVN) nuclei. Peripheral injection of losartan blocked this drinking response and prevented the induction of Fos-ir in each of these brain regions. Hypovolemia produced by polyethylene glycol (PEG) produced a robust water intake but no evidence of sodium appetite, and it induced Fos-ir in SFO, MnPO, and PVN. Peripheral injection of losartan did not affect this drinking response. Fos-ir induced by PEG in SFO and MnPO was reduced by treatment with losartan, while that induced in the PVN was further increased by losartan. Sodium depletion with furosemide and low-sodium diet produced a strong sodium appetite and induced Fos-ir in SFO and MnPO. Treatment with losartan completely blocked the sodium appetite, as well as the induction of Fos-ir in these brain regions. These data indicate that endogenous production of ANG II and action at forebrain receptors is critically involved in depletion-related sodium appetite in mice. The absence of an effect of losartan on PEG-induced drinking suggests the critical involvement of other factor(s) such as arterial or venous baroreceptor input, and we discuss how this factor could also explain why peripheral ANG II is not dipsogenic in mice.     

Tumor anorexia: effects on neuropeptide Y and monoamines in paraventricular nucleus

Paraventricular (PVN) concentrations of neuropeptide Y (NPY), serotonin (5-HT) and dopamine (DA) in anorectic tumor-bearing (TB) rats were measured before and after tumor resection. At onset of anorexia in TB versus non-tumor bearing (NTB) Controls 5-HT increased from 12.19+/-0.49 pg/microg to 14.89+/-0.81 pg/microg ( P<0.05 ) while DA and NPY decreased from 7.34+/-0.42 pg/microg to 4.97+/-0.56 pg/microg and 23.47+/-4.27 pg/microg to 13.64+/-1.44 pg/microg, respectively ( P<0.05 ). After tumor resection, these neuromediators normalized when compared to sham-operated NTB rats. NTB pair-fed Controls were also studied. We conclude that the increased 5-HT and the decreased DA and NPY concentrations in PVN are associated with cancer anorexia and that the NPY food stimulatory effect is linked to serotoninergic and dopaminergic systems in hypothalamus.     

Intracerebroventricular 5,7-DHT alters the in vitro function of rat cortical GABAA/benzodiazepine chloride ionophore receptor complexes.

We have earlier presented data indicating that the anxiolytic-like effect obtained in rats after depletion of brain 5-HT by means of PCPA or 5,7-DHT treatment is indirect and appears to involve the GABAA/benzodiazepine chloride ionophore receptor complex (GABAA/BDZ-RC), and that it is abolished by adrenalectomy. In the present series of experiments we have therefore investigated the 36Cl(-)-uptake in rat synaptoneurosomal preparations of central cortices from 5,7-DHT- and SHAM-lesioned animals. The GABA as well as the 3 alpha,5 alpha-tetrahydrodeoxycorticosterone (THDOC) induced picrotoxin-sensitive increase in 36Cl(-)-uptake was significantly lower than that observed in the SHAM-lesioned animals, indicating that the 5,7-DHT lesion has rendered the GABAA/BDZ-RC subsensitive to two of its tentative endogenous ligands. This effect of the 5,7-DHT lesion on the function on the GABAA/BDZ-RC was reversed by adrenalectomy, indicating that an intact adrenocortical function is required for the development of GABAA/BDZ-RC subsensitivity in 5,7-DHT-lesioned rats. A tentative conclusion of these findings is that the 5,7-DHT lesion induces an increase in release of GABA and/or barbiturate-like steroids and that this increase is reversed by adrenalectomy. The findings from these in vitro studies parallel those from our previous behavioral experiments and provide further support for the notion that a decreased serotonergic influence in the central nervous system may, possibly via the adrenocortical system, enhance the function of the GABAA/BDZ-RC.     

Effects of imipramine and serotonin-2 agonists and antagonists on serotonin-2 and beta-adrenergic receptors following noradrenergic or serotonergic denervation

The effects of chronic (14 day) administration of the tricyclic antidepressant imipramine, the serotonin-2 (5-HT2) antagonist ketanserin, and the serotonin agonist quipazine on 5-HT2 receptor binding parameters and 5-HT2-mediated behavior were examined in rats with or without prior serotonergic denervation [via 5,7-dihydroxytryptamine (5,7-DHT)] or noradrenergic denervation [via N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4)]. Chronic administration of imipramine, ketanserin, or quipazine produced a marked reduction in the number of 5-HT2 binding sites which was accompanied by reductions in the 5-HT2-mediated quipazine-induced head shake response. In animals receiving DSP4 or 5,7-DHT lesions and continuous vehicle treatment, beta-adrenergic receptor binding sites were significantly up-regulated while 5-HT2 receptor binding sites did not change. Imipramine normalized the lesion-induced increases in beta-adrenergic binding observed in DSP4 and 5,7-DHT-lesioned rats but failed to down-regulate beta-adrenergic binding sites below non-lesioned control levels. Chronic imipramine, ketanserin, and quipazine reduced quipazine-induced head shakes and down-regulated 5-HT2 binding sites in rats with noradrenergic denervation. While imipramine, ketanserin, and quipazine all down-regulated 5-HT2 binding sites in animals with serotonergic denervation, only imipramine's ability to reduce quipazine-induced head shakes was attenuated in 5,7-DHT-lesioned rats. The present results suggest that imipramine-induced down-regulation of 5-HT2 receptors may not involve presynaptic 5-HT mechanisms, and imipramine-induced alterations in 5-HT2 sensitivity as reflected in the quipazine-induced head shake may, in part, be influenced by beta-adrenergic receptors.     

Stimulatory role for brain serotoninergic system on prolactin secretion in the male rat.

Systemic administration of parachlorophenylalanine (PCPA, 100 mg/kg sc on alternate days X two times), a blocker of serotonin (5-HT) synthesis, considerably decreased brain 5-HT and plasma prolactin (PRL) levels in young male rats. Intraventricular (IVT) administration of 5,7-dihydroxytryptamine (5,7-DHT, 200 mug/20 mul), a neurotoxic drug which destroys 5-HT nerve terminals, induced, 3, 12, and 30 days after treatment, a marked depletion of brain 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) and considerably reduced plasma PRL levels at each time interval. Feeding of rat for up to 4 days with a tryptophan (TP)-deficient diet, caused a depletion of brain 5-HT and 5-HIAA contents and did not modify plasma PRL levels. Addition of TP (2 g/kg of diet) to the TP-deficient diet resulted in increased brain 5-HT and 5-HIAA contents and significantly increased PRL levels. These data provide evidence for the role of the 5-HT system in the maintenance of tonic PRL secretion.     

Serotonin-mediated increases in the extracellular levels of beta-endorphin in the arcuate nucleus and nucleus accumbens: a microdialysis study

Although the involvement of both endogenous opioid and serotonergic systems in modulation of pain and emotion was suggested, the neurochemical interaction between these systems in the brain has not previously been studied directly. Herein, the effects of the local application of serotonin (5-HT) and fluoxetine (a 5-HT reuptake inhibitor) on extracellular levels of beta-endorphin in the arcuate nucleus and nucleus accumbens were assessed in freely moving rats using in vivo microdialysis. The mean basal concentrations of beta-endorphin in dialysates obtained from the arcuate nucleus and nucleus accumbens were 259.9 and 143.3 pM, respectively. Specific lesion of the serotonergic system by 5,7-dihydroxytryptamine (5,7-DHT) caused a significant decrease in these dialysate beta-endorphin levels. When 5-HT (0.25-5 microM) was added to the perfusion solution, the levels of beta-endorphin in the dialysate from the arcuate nucleus increased (186-296% of baseline), in a concentration-dependent manner. In the nucleus accumbens, 0.5 and 2 microM 5-HT in the perfusion fluid did not affect the levels of beta-endorphin in the dialysate, whereas 5 and 10 microM 5-HT caused an increase of approximately 190% of baseline. When fluoxetine (250 microM) was present in the perfusing solution, the levels of beta-endorphin in the dialysates from the arcuate nucleus and nucleus accumbens increased two- to threefold. This effect was not obtained in the 5,7-DHT-lesioned rats. Thus, 5-HT, either endogenously or exogenously delivered, appears to facilitate the release of beta-endorphin in the arcuate nucleus and nucleus accumbens. This indication of an interaction between serotonergic and endorphinic systems may be relevant for assessing pain and mood disorder circuits and the mode of action of antidepressant drugs.     

The 5,7-DHT-induced anticonflict effect is dependent on intact adrenocortical function.

We have recently reported that the anxiolytic-like effect observed in rats severely depleted of brain serotonin (5-HT) by means of 5,7-DHT is indirect and probably involves the GABA(A)/benzodiazepine chloride ionophore receptor complex (GABAA/BDZ-RC). One tentative explanation for this effect considered the involvement of corticosteroids. In the present series of experiments we have therefore investigated the effect of adrenalectomy (ADX) on the 5,7-DHT-induced anxiolytic-like effect displayed by rats in Vogel's conflict test. ADX totally abolished the anticonflict effect of the 5,7-DHT lesion. Replacement treatment with corticosterone, but not with dexamethasone, reinstated the anticonflict effect. These results indicate that an intact adrenocortical function, possibly via brain steroid type I receptors, is required for the expression of the 5,7-DHT-induced anxiolytic-like effect. It is postulated that ADX lowers the concentration of endogenous positive modulators at the GABAA/BDZ-RC to a level no longer sufficient to produce anxiolytic-like effects in 5,7-DHT-lesioned animals. The finding that 5,7-DHT-lesioned animals were more sensitive than sham-lesioned controls to the anticonflict effect of the barbiturate-like corticosteroid THDOC provides further support for the contention that an increased endogenous activity at the GABAA/BDZ-RCes is involved in the anxiolytic-like effect observed in rats with a severe depletion of brain 5-HT.     

Dissociation of the plasticity of 5-HT1A sites and 5-HT transporter sites

To study the early effects of neonatal 5,7-dihydroxytryptamine lesions on 5-hydroxytryptamine_1A (5-HT_1A) receptors, we measured regional [³H]8-OH-DPAT-labeled 5-HT_1A sites in binding assays and compared them to our previous studies of [³H]paroxetine-labeled 5-HT transporter sites during the first month in the same rats. While there were significant time- and dose-dependent effects of 5,7-DHT on 5-HT transporter sites, there were no significant changes in 5-HT_1A sites in cortex, hippocampus, diencephalon, brainstem, cerebellum, or spinal cord. 5,7-DHT lesions also did not alter the K_i of Gpp(NH)p at brainstem 5-HT_1A sites or the K_i of 5-HT in cortex or brainstem in the presence or absence of GTPS or Gpp(NH)p. There were significant regional differences between the density of 5-HT_1A sites and 5-HT transporter sites. The ontogeny of brainstem 5-HT_1A sites was a pattern of increases until three weeks postnatal, and 5,7-DHT lesions did not alter the ontogeny of 5-HT_1A sites. These data suggest differential plasticity of 5-HT_1A and 5-HT transporter binding sites during the first month after neonatal 5,7-DHT lesions.     

Improvement by repeated administration of 6R-tetrahydrobiopterin of 5,7-dihydroxytryptamine-induced abnormal behaviors in immature rats

To clarify the therapeutic effects of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (6R-BH(4)) on the abnormal behaviors induced by neonatal 5,7-dihydroxytryptamine (5,7-DHT, 100 microg; i.c.v.) treatment in immature rats, 6R-BH(4) (10-40 mg/kg) was administered intraperitoneally from 22nd to 28th days or only once on the 28th day. The locomotion activities decreased dramatically in 5,7-DHT-treated rats (p<0.01; as compared to controls) on the 28th day. The reduced locomotion was recovered dose-dependently by repeated administration of 6R-BH(4), whereas it was not altered after a single injection of 6R-BH(4). In addition, repeated administration of 6R-BH(4) significantly facilitated 5-HT turnover ratio (5-HIAA/5-HT) in the striatum, cerebral cortex, and cerebellum. These findings suggest that the behavioral restoration by 6R-BH(4) might be due to the enhancement of 5-HT turnover by accumulated but not a single dose of 6R-BH(4).     

Rotational responses to serotonergic and dopaminergic agonists after unilateral dihydroxytryptamine lesions of the medial forebrain bundle: co-operative interactions of serotonin and dopamine in neostriatum.

Rats with unilateral 5,7-DHT lesions, but not 5,6-DHT lesions, showed rotational responses to 5-HTergic drugs (5MeODMT and fenfluramine) that were qualitatively similar to those induced by DAergic drugs (apomorphine and amphetamine) after 6-OHDA lesions. However, 5,7-DHT-lesioned rats also themselves showed rotational responses to DAergic drugs. The merits and limitations of a unilateral 5,7-DHT-lesioned rotating rat model for studying 5-HTergic function are discussed. It is suggested that 5-HT and DA may function in a co-operative manner in the striatum. These findings may be important for the rational pharmacotherapy of Parkinson's disease in which 5-HT as well as DA has been shown to be substantially depleted.     

Time course of expression and function of the serotonin transporter in the neonatal rat's primary somatosensory cortex

Immunocytochemical and autoradiographic techniques were employed to determine the time course of expression of the serotonin (5-HT) transporter (SERT) on thalamocortical afferents in the rat's primary somatosensory cortex (S-I), and to correlate this expression to the transient vibrissae-related patterning of 5-HT immunostaining previously described. In additional in vivo and in vitro experiments, 5-HT and 3 H-5-HT were applied directly to the cortices of untreated and 5,7-dihydroxytryptamine-treated (5,7-DHT) rats in order to determine the period during which SERT functions on thalamocortical axons to take up 5-HT. In postnatal rats, SERT immunohistochemistry revealed a somatotopic patterning in S-I that persisted until P-15, which is 6 days after the disappearance of the vibrissae-related 5-HT immunostaining. 3 H-citalopram autoradiography revealed a vibrissae-related pattern in layer IV of S-I until at least P-30. Following destruction of raphe-cortical afferents with 5,7-DHT on the day of birth, this binding pattern remained visible until at least P-25, indicating that SERT located on thalamocortical axons is responsible for the 3 H-citalopram patterning observed in S-I. Tissue from 5,7-DHT-treated rats that had 5-HT applied directly to their cortices revealed a normal vibrissae-related pattern of 5-HT immunostaining in S-I at P-7 and P-11 but only a faint pattern at P-13 and none at P-14. In addition, 3 H-5-HT injected directly into S-I labeled layer IV barrels at P-6 and P-12 but not at P-18. The results of these experiments demonstrate that SERT is expressed by thalamocortical afferents and remains functional long after the vibrissae-related 5-HT immunostaining in cortex disappears.     

Significant correlation between cerebrospinal fluid and brain levels of norepinephrine, serotonin and acetylcholine in anesthetized rats

The present study was undertaken to determine cerebrospinal fluid (CSF) and brain levels of norepinephrine (NE), serotonin (5-HT) and their metabolites--3,4-dihydroxyphenylacetic acid (DOPAC), 4-hydroxy-3-methoxyphenylacetic acid (HVA) and 5-hydroxyindole-3-acetic acid (5-HIAA)--in rats pretreated with 6-hydroxydopamine (6-OHDA) or 5,7-dihydroxytryptamine (5,7-DHT). In the 6-OHDA pretreated rats, both CSF and brain concentrations of NE, DOPAC and HVA sustained significant decreases as compared with those in non-treated rats. Positive and significant correlations between CSF and brain levels were observed in respect to NE, DOPAC and HVA. In 5,7-DHT pretreated rats, both CSF and brain concentrations of 5-HT and 5-HIAA were significantly decreased. A positive and significant correlation between CSF and brain levels in respect to 5-HT and 5-HIAA was observed. Further studies were carried out to determine ACh levels of both the CSF and the brain in microspheres (MS)-treated rats, which are used as a model of microembolization. The CSF ACh concentrations in MS-treated groups were significantly decreased as compared with those in non-treated rats. The brain ACh contents also tended to decrease in this group. A positive and significant correlation was observed between CSF and brain levels of ACh. These findings suggest that NE, 5-HT and ACh concentrations in the CSF are direct indications of central noradrenergic, serotonergic and cholinergic nerve activity, respectively.     

[3H]Paroxetine Binding and Serotonin Content of Rat Cortical Areas, Hippocampus, Neostriatum, Ventral Mesencephalic Tegmentum, and Midbrain Raphe Nuclei Region Following p-Chlorophenylalanine and p-Chloroamphetamine Treatment

The agents p-chlorophenylalanine (PCPA) and p-chloroamphetamine (PCA) deplete brain serotonin (5-HT) levels by two different mechanisms; PCPA inhibits the enzyme tryptophan hydroxylase, whereas PCA has a neurotoxic action on certain 5-HT neurons. The parameters of [3H]paroxetine binding to homogenates prepared from the cerebral cortex of rats treated with PCPA, PCA, or saline; vehicle were investigated. The tissue concentrations of 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) were also determined by HPLC in the same brain samples. After PCPA treatment, neither the maximum binding capacity (Bmax) nor the dissociation constant (KD) of [3H]paroxetine for the 5-HT uptake recognition site differed from controls despite a substantial reduction in the concentration of 5-HT and 5-HIAA. In contrast, significant changes in both the Bmax and KD values were observed in the cerebral cortex of rats treated with PCA. Furthermore, [3H]paroxetine binding and tissue concentrations of 5-HT and 5-HIAA were measured in the following different regions of the rat brain: cingulate, parietal, and visual cortical areas; dorsal and ventral hippocampus; rostral and caudal halves of neostriatum; ventral mesencephalic tegmentum; and midbrain raphe nuclei region after administration of PCPA, PCA, or saline vehicle. There was an excellent correlation between regional 5-HT levels and specific [3H]paroxetine binding in control and PCA-treated rats although this correlation was lost after PCPA treatment. Under these conditions, the 5-HT innervation remains unchanged whereas the concentration of 5-HT and 5-HIAA is greatly reduced. Thus, [3H]paroxetine binding appears to provide a reliable marker of 5-HT innervation density within the mammalian CNS.     

Osmotic regulation of estrogen receptor-beta expression in magnocellular vasopressin neurons requires lamina terminalis

Estrogen receptor-beta (ER-beta) expression in rat magnocellular vasopressin (VP) neurons of the supraoptic and paraventricular nuclei (SON and PVN, respectively) becomes undetectable after 72 h of 2% NaCl consumption. To test the hypothesis that osmosensitive mechanisms that originate in the region of the organum vasculosum lamina terminalis (OVLT) control ER-beta expression in the SON and PVN, animals were water deprived after electrolytic lesions were performed on the area anterior to the ventral third ventricle (AV3V). Such lesions prevent osmotic stimulation of VP release. Four weeks after surgery, male rats [lesioned (n = 16) or sham (n = 14)] were water deprived for 48 h or allowed water ad libitum. Water deprivation eliminated ER-beta-immunoreactivity (-ir) in SON and magnocellular PVN of sham-lesioned animals. Fos-ir was evident in these neurons, and plasma osmolality (Posm) and hematocrit (Ht) were significantly elevated compared with the sham-hydrated rats (Posm, 304 +/- 1 vs. 318 +/- 2 mosmol/kgH2O; P < 0.001; Ht, 49.6 +/- 0.6 vs. 55.0 +/- 0.9%; P < 0.001). ER-beta expression was comparable in sham-hydrated, AV3V-hydrated, and 6 of 8 AV3V-dehydrated rats despite significant increases in Posm in both groups (AV3V hydrated, 312 +/- 2; AV3V dehydrated, 380 +/- 10 mosmol/kgH2O; P < 0.001). OVLT was not ablated in the AV3V-dehydrated rats in which ER-beta was depleted. Fos-ir was low or undetectable in SON in the AV3V-hydrated animals despite elevated Posm values. In AV3V-dehydrated rats, Fos-ir was significantly less than in sham-dehydrated animals but was significantly increased compared with the sham-hydrated group. This could reflect activation by nonosmotic parameters that do not inhibit ER-beta expression. These data support the hypothesis that inhibition of ER-beta expression in the SON by osmotic stimulation is mediated by osmoreceptive neurons in the lamina terminalis.     

Further Studies on the Nature of Postsynaptic Dopamine Uptake and Metabolism in Rat Striatum: Sodium Dependency and Investigation of a Possible Role for Carrier-Mediated Uptake into Serotonin Neurons

The nature of postsynaptic sites involved in the uptake and metabolism of striatal 3,4-dihydroxyphenylethylamine (dopamine, DA) was investigated. The accumulation of [3H]DA (10(-7) M) into slices of rat striatum was found to be greatly dependent (greater than 99%) on the presence of sodium ion in the incubation medium. However, the formation of the [3H]dihydroxyphenylacetic acid (DOPAC) and [3H]homovanillic acid (HVA) was only partially reduced in the absence of sodium (DOPAC, 27% of control; HVA, 47% of control). Inhibition of carrier-mediated DA neuronal uptake with nomifensine (10(-5) M) significantly decreased DA accumulation (18% of control) and [3H]DOPAC formation (62% of control), but enhanced [3H]HVA production (143% of control). Inhibition of the 5-hydroxytryptamine (5-HT, serotonin) neuronal uptake system with fluoxetine (10(-6) M) or selective 5-HT neuronal lesions with 5,7-dihydroxytryptamine (5,7-DHT) had no effect on [3H]DOPAC or [3H]HVA formed from [3H]DA in the presence or absence of nomifensine. These results demonstrate that the uptake and subsequent metabolism of striatal DA to DOPAC and HVA is only partially dependent on carrier-mediated uptake mechanism(s) requiring sodium ion. These data support our previous findings suggesting a significant role for synaptic glial cell deamination and O-methylation of striatal DA. Further, experiments with fluoxetine or 5,7-DHT suggest that 5-HT neurons do not significantly contribute in the synaptic uptake and metabolism of striatal DA.     

Role of 5-hydroxytryptamine in the regulation of brain neuropeptides in normal and diabetic rat

The effect of 5-hydroxytryptamine (5-HT) alteration on brain dopamine (DA), norepinephrine (NE), beta-endorphin (beta E) and immunoreactive insulin (IRI) was studied in Sprague-Dawley diabetic and control rats. Diabetes was induced using alloxan (45 mg/kg), 15 days prior to sacrificing. Both control and diabetic animals were treated with either p-chlorophenylalanine (PCPA, 300 mg/kg) 3 days prior to sacrificing or fluoxetine (10 mg/kg) twice daily for 3 days. PCPA treatment significantly decreased brain content of 5-HT and 5-hydroxyindole acetic acid (5-HIAA) while it caused significant increase and decrease in brain beta E and insulin levels, respectively, in both normal and diabetic rat. Meanwhile, the administration of fluoxetine resulted in significant increase in brain content of 5-HT, DA, NE and insulin but significant decline of beta E in diabetic and saline control rats. The results of this experiment indicate that 5-HT may be regulating both beta E and insulin regardless of the availability of pancreatic insulin.