Catecholamine depletion modulates serum LH levels, GAD67 mRNA, and GABA synthesis in the goldfish.

It is established that dopamine inhibits while GABA stimulates LH release in goldfish. In this study, we examine dopaminergic regulation of GABAergic activity in the hypothalamus of early recrudescent female goldfish (Carassius auratus). We utilize a unique technique that permits concomitant quantification and correlation of in vivo GAD65 and GAD67 mRNA with GABA synthesis rate in response to decreased dopamine levels. Catecholamine depletion was achieved by treatment with alpha-methyl-para-tyrosine methyl ester (alphaMPT; 240 microg/g body weight), an inhibitor of tyrosine hydroxylase. Endogenous GABA levels were increased by intraperitoneal administration of gamma-vinyl GABA (GVG; 300 microg/g body weight), an inhibitor of the GABA catabolic enzyme GABA transaminase. Dual treatment of GVG+alphaMPT increased serum LH levels 4-fold. However, LH mRNA levels in the pituitary remained stable, suggesting that treatments affected secretion and not synthesis. In the hypothalamus, GABA synthesis rates increased 30% in response to alphaMPT treatment. This was correlated (r=0.61; p<0.05) to increased levels of GAD67 mRNAs but not GAD65 (r=0.14; p>0.05). These observations suggest that catecholamines inhibit GABA synthesis in the goldfish hypothalamus through isoform specific regulation of GAD67.

Lack of behavioral effects of monoamine depletion in healthy subjects.

This study was designed to determine the behavioral effects of a reduction in catecholamine and indoleamine function in healthy subjects. Eight healthy subjects received the tyrosine hydroxylase inhibitor, alpha-methyl-para-tyrosine (AMPT) in combination with a full-strength tryptophan-depleting amino acid drink during one 4-day test session, and AMPT and tryptophan-supplemented amino acid drink (n = 2), or a 25% strength tryptophan-depleting amino acid drink (n = 6) during a second 4-day test session. The combined administration of AMPT and the tryptophan-free amino acid drink did not produce statistically significant or even clinically noticeable changes in mood among the healthy subjects. The implications of these observations for the monoamine hypotheses of depression are discussed.

Pharmacological model of catecholamine depletion in the hypothalamus of fetal and neonatal rats and its application.

1. The present study aimed to develop a pharmacological model of catecholamine (CA) depletion in the hypothalamus during the period of its morphofunctional development, i.e. in fetal and neonatal rats of both sexes. 2. In the first series of experiments, pregnant females and, hence, fetuses were systemically treated daily from the embryonic day (E) 13 to E20 with the inhibitor of the CA synthesis alpha-methyl-m-tyrosine. The CA concentrations were subsequently measured in the fetal hypothalamus at E21 by high performance liquid chromatography with electrochemical detection (HPLC-ED). In the second series of experiments, neonatal rats were injected with neurotoxin, 6-hydroxydopamine and/or alpha-methyl-m-tyrosine daily from the 2nd postnatal day (P2) to P10. 3. The HPLC-ED assay of hypothalamic catecholamines (CA's) at E21 and P11 showed that both in fetuses and neonates, alpha-methyl-m-tyrosine caused more than 50% depletion of hypothalamic noradrenaline and adrenaline, while the dopamine (DA) level remained unchanged. The combined treatment of neonatal rats with alpha-methyl-m-tyrosine and 6-hydroxydopamine resulted additionally in a 25% decreased level of DA. 4. The influence of CA deficiency on the developing hypothalamic CA system was further evaluated by measuring [3H]DA uptake by nervous tissue in vitro. 5. The CA deficiency caused a 50% drop of [3H]DA uptake by the hypothalamic tissue in treated fetuses suggesting a stimulating effect of CA's on the early development of the CA system. In pharmacologically treated neonatal rats [3H]DA uptake remained at the control level showing no influence of the CA deficiency on the developing CA system after birth. 6. The usefulness of the proposed pharmacological model for studying of CA influence on differentiating hypothalamic target neurons is discussed.

In vivo tryptophan hydroxylase activity in rat major cerebral arteries is decreased by dorsal raphe nucleus lesions.

The in vivo presence of tryptophan hydroxylase activity in rat major cerebral arteries as well as the possible origin of the structure containing it were explored. Enzyme activity was appraised by accumulation of 5-hydroxytryptophan after inhibition of aromatic L-amino acid decarboxylase. Decarboxylase inhibition evoked a significant increase in 5-hydroxytryptophan levels in rat cerebral arteries, striatum, hippocampus, hypothalamus, and plasma but had no effect on aorta. p-Chlorophenylalanine reduced 5-hydroxytryptophan accumulation in the cerebral vessels and brain nuclei, whereas alpha-methyltyrosine did not modify it except in hypothalamus, where it was enhanced. alpha-Methyltyrosine significantly reduced noradrenaline levels in cerebral arteries and L-dopa accumulation after inhibition of the decarboxylase in striatum. Dorsal raphe nucleus lesioning significantly diminished 5-hydroxytryptophan formation in cerebral arteries, striatum, and hypothalamus, without affecting it in hippocampus. Lesion of median raphe nucleus reduced 5-hydroxytryptophan accumulation in hippocampus and in hypothalamus but not in cerebral blood vessels or striatum. Superior cervical ganglia removal decreased noradrenaline levels in cerebral blood vessels without affecting 5-hydroxytryptophan accumulation. These results indicate the presence of a functionally active tryptophan hydroxylase in rat cerebral arteries associated with fibers originating from dorsal raphe nucleus. This supports that rat major cerebral arteries receive serotonergic innervation from central origin.

[Antinociceptive effects of Kami-kihi-to in mice].

Oral administration of Kami-kihi-to (KMK) dose-dependently inhibited the response to acetic acid-induced writhing in mice. The KMK-induced antinociceptive action was reduced by pretreatment with yohimbine, an alpha 2-adrenergic antagonist, or cyproheptadine, a serotonergic antagonist, but not naloxone, an opiate antagonist. The antinociceptive action of KMK was clearly reduced by pretreatment with alpha-methyl-DL-p-tyrosine, reserpine or p-chlorophenylalanine or by simultaneous treatment with diethyldithiocarbamate, all of which are monoamine synthetic inhibitors or monoamine depletors. After spinal transection, the antinociceptive effect of KMK was markedly reduced. These findings suggest that the antinociceptive action of KMK may be related to pain inhibitory systems such as the serotonergic and noradrenergic systems at the supraspinal level.

Disulfiram and diethyldithiocarbamate intoxication affects the storage and release of striatal dopamine.

Acute intoxication and chronic therapy with the alcohol consumption deterrent dithiocarbamate disulfiram have been associated with several neurological complications perhaps involving the impairment of neurotransmitter pathways. In this study we have tested the hypothesis that dopaminergic malfunction is a critical component in disulfiram-evoked neurotoxicity. Disulfiram antagonized the in vitro striatal binding of [3H]tyramine, a putative marker of the vesicular transporter for dopamine, and the uptake of [3H]dopamine into striatal synaptic vesicles, with inhibitory constants (Ki) in the range of reported blood dithiocarbamate levels in treated alcoholics. Furthermore, disulfiram provoked a loss of radioactivity from [3H]dopamine-preloaded striatal vesicles, when added directly to the incubation mixture. Several metal-containing fungicide analogs were also potent displacers of specifically bound [3H]tyramine. Diethyldithiocarbamate (DDC), the major metabolite of disulfiram, had none of these effects. The intraperitoneal injection of a high dose of disulfiram and DDC into rats, mimicking acute intoxication, induced in vivo overflow of striatal dopamine from both a reserpine-sensitive (vesicular) and an alpha-methyl-p-tyrosine-sensitive (cytoplasmic) pool. The vesicular component of in vivo dopamine release resulted mainly from a direct activity of disulfiram, on the organelles (interaction with the carrier for dopamine plus membrane permeabilization) and indirectly through the mediation of serotonergic 5-HT3 receptors. DDC acted poorly at the vesicle membrane, and the in vivo releasing effect of dopamine was only partially prevented by the inhibition of 5-HT3 receptors, thus suggesting the role of additional mechanisms. It is concluded that disulfiram intoxication may acutely disrupt dopamine balance, an effect probably underlying some of the central neurotoxic, extrapyramidal symptoms associated with dithiocarbamate overdose.

Effects of administration of some monoamine-synthesis blockers and precursors on ovariectomy-induced rise in plasma gonadotropin II in the catfish Heteropneustes fossilis.

In the present study, effects of three daily i.p. injections of some monoamine (MA)-synthesis blockers and pre-cursors on plasma gonadotropin (GTH-II) levels were investigated in 3-week ovariectomized catfish, and the effects were correlated with changes in hypothalamic MA contents. Administration of alpha-methylparatyrosine (alpha-MPT; 250 micrograms/g BW, a tyrosine hydroxylase inhibitor) significantly decreased the ovariectomy-induced rise in GTH-II compared to that of the sham control group. Injection of L-dihydroxyphenylalanine (10 micrograms/g BW) in the alpha-MPT-treated fish elevated the GTH-II level significantly over that of the sham control group but not to the level of the ovariectomized fish. Administration of noradrenaline (NA; 5 micrograms/g BW) in combination with alpha-MPT counteracted the effect of the latter and maintained the plasma GTH-II level at that of the ovariectomized fish. Plasma GTH-II level was decreased significantly in the diethyldithiocarbamate (10 micrograms/g BW, a dopamine-beta-hydroxylase inhibitor)-injected fish compared to that of the sham and ovariectomized control groups. Administration of para-chlorophenylalanine (p-CPA; 100 micrograms/g BW, a tryptophan hydroxylase inhibitor) decreased the GTH-II level significantly compared to that of the ovariectomized group. Supplementation of 5-hydroxytryptophan (20 micrograms/g BW) with p-CPA nullified the latter's effect and maintained the GTH-II level at that of the ovariectomized fish. The administration of both p-CPA and alpha-MPT significantly reduced plasma GTH-II to the lowest mark compared to that of the sham, ovariectomized, and all other treatment groups. These results clearly show that the ovariectomy-induced rise in GTH-II was mediated through simultaneous activation of hypothalamic serotonergic and NA-ergic and suppression of dopaminergic mechanisms.

Evidence for a dopaminergic involvement in the natriuretic action of centrally administered renin.

Intracerebroventricular (IVT) administration of renin (R) to conscious male hydrated rats induces an increase in sodium excretion. The involvement of brain dopaminergic neurons in the renal action of IVT-R was investigated. Renin-induced natriuretic action was prevented by domperidone and by inhibition of tyrosine hydroxylase activity with alpha-methyl-p-tyrosine treatment. In addition, this effect was absent following selective central dopaminergic denervation with 6-hydroxydopamine (IVT) in combination with desmethylimipramine (IP). Our results suggest that renin acts centrally, at least in part, via an interaction with endogenous dopamine systems.

Methamphetamine-induced hyperthermia and dopaminergic neurotoxicity in mice: pharmacological profile of protective and nonprotective agents.

Neurotoxic doses of methamphetamine (METH) can cause hyperthermia in experimental animals. Damage sustained to dopaminergic nerve terminals by this stimulant can be reduced by environmental cooling or by pharmacological manipulation which attenuates the hyperthermia. Many pharmacological agents with very diverse actions protect against METH-induced neuropathology. Several of these compounds, as well as drugs which do not protect, were investigated to determine if there was a relationship between protection and METH-induced hyperthermia. Mice received METH with or without concurrent administration of other drugs and core (i.e., colonic) temperature was monitored during treatment. The animals were sacrificed > or = 5 days later and neostriatal tyrosine hydroxylase activity and dopamine were measured. Core temperature was significantly elevated (> or = 2 degrees C) in mice treated with doses of METH which produced > or = 90% losses in striatal dopamine but not in mice less severally affected (only 50% loss of dopamine). Concurrent treatment of mice with METH and pharmacological agents which protected partially or completely from METH-induced toxicity also prevented the hyperthermic response (i.e., dopamine receptor antagonists, fenfluramine, dizocilpine, alpha-methyl-p-tyrosine, phenytoin, aminooxyacetic acid and propranol). These findings are consistent with the hypothesis that the hyperthermia produced by METH contributes to its neuropathology. However, studies with reserpine, a compound which dramatically lowers core temperature, demonstrated that hyperthermia per se is not a requirement for METH-induced neurotoxicity. Although core temperature was elevated in reserpinized mice treated with METH as compared with reserpinized control mice, their temperatures remained significantly lower than in nonreserpinized control mice. However, the hypothermic state produced in the reserpinized mice did not provide protection from METH-induced toxicity. These data demonstrate that hyperthermia per se contributes to but is not solely responsible for the METH-induced neuropathology.

Effects of a selective alpha 2-adrenoceptor antagonist, atipamezole, on hypothalamic histamine and noradrenaline release in vivo.

In vivo microdialysis was used to study the effects of a potent and selective alpha 2-adrenoceptor antagonist, atipamezole, on histamine and noradrenaline release from the medial hypothalamus in anesthetized rats. Local perfusion with atipamezole via the microdialysis probe increased histamine release significantly and dose-dependently. However, the effect of systemic administration of atipamezole (1 mg/kg) was opposite: it significantly decreased histamine release. Local and systemic administration of atipamezole produced an approx. 2-fold increase in noradrenaline release. To study the modulatory effect of noradrenergic neurons on histamine release, noradrenaline synthesis was inhibited with alpha-methyl-p-tyrosine. In the microdialysis experiment, rats that received alpha-methyl-p-tyrosine exhibited no decrease, but rather a slight increase in histamine release in response to systemic atipamezole administration. These results show clearly that atipamezole enhances noradrenaline release in vivo from rat hypothalamus and its effects on histamine release are dependent on the route of drug administration.

Mechanisms of altered LH secretion in neonatally oestrogenized male rats.

It is well known that the control of LH secretion depends on the steroid milieu during the postnatal period. In this study LH secretion was analysed in adult male rats injected neonatally with 500 micrograms oestradiol benzoate (1) after orchidectomy, (2) after selective elimination of androgens by destruction of Leydig cells with ethylene dimethane sulphonate (EDS), and (3) after removal in orchidectomized animals of Silastic capsules containing testosterone. In addition, (4) in vivo and in vitro LH secretion in response to LHRH agonist and antagonists, (5) the hypothalamic LHRH content, (6) the basal and stimulated in vitro LHRH release, and (7) the LH responses after administration of naloxone (2 mg/kg), alpha-methyl-p-tyrosine (alpha-MPT; 250 mg/kg), N-methyl-D-aspartic acid (NMDA, 15 mg/kg) or kainic acid (KA; 15 mg/kg) were also examined. Our data indicated that (1) the LH response after orchidectomy, after EDS administration and after removal of Silastic capsules containing testosterone was diminished in oestrogenized male rats, (2) the pituitaries from oestrogenized males retained responsiveness to LHRH, (3) hypothalamic LHRH content was reduced in oestrogenized males, but the hypothalamus from oestrogenized males released more LHRH than those of control groups both under basal conditions or after depolarization, (4) alpha-MPT decreased LH secretion only in oestrogenized males, and (5) NMDA and KA stimulated LH only in oestrogenized males. We conclude that in oestrogenized male rates the loss of sensitivity to the negative feedback action of testosterone on LH secretion was not due to decreased pituitary responsiveness to LHRH stimulation or to the inherent damage of LHRH neurones.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of catecholamine synthesis inhibitors and adrenergic receptor antagonists on restraint-induced LH release.

Acute stress is known to increase LH secretion and the release of central norepinephrine (NE) in intact rats. Studies were performed to analyse the ole of catecholamines in acute stress-induced LH release in male rats. Injection of alpha-methyl-p-tyrosine (alpha MPT) and diethyldithiocarbamate (DDC), catecholamine synthesis inhibitors, significantly decreased both hypothalamic concentration of NE and serum LH. Restraint for 30 min evoked an increase in serum LH in saline-treated rats, whereas alpha MPT and DDC administration blocked the stress-induced LH release. The effects of alpha 1-, alpha 2- and beta-adrenoreceptor antagonists on the LH response to restraint stress were also studied. Propranolol treatment did not modify serum LH in either unstressed or stressed rats. The two alpha-adrenergic receptor antagonists prazosin and yohimbine prevented the restraint-induced LH release; however, prazosin but not yohimbine significantly decreased the serum concentration of LH in unstressed rats. These data suggest that the acute stress-induced increase in LH secretion is mediated through the activation of alpha 2-adrenergic receptors.

Changes in hypothalamic catecholamines, dopamine-beta-hydroxylase, and phenylethanolamine-N-methyltransferase in the catfish Heteropneustes fossilis in relation to season, raised photoperiod and temperature, ovariectomy, and estradiol-17 beta replacement.

In Heteropneustes fossilis, contents and turnovers of hypothalamic catecholamines (CA) and activities of dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) showed significant seasonal variations with significantly high day values. The seasonal pattern of dopamine (DA) on one hand and that of noradrenaline (NA) and adrenaline (A) on the other hand showed an inverse relationship, the former decreasing and the latter increasing during the progress of gonadal recrudescence. The DBH and PNMT levels were low in the resting phase and increased to the peak in the prespawning (DBH) and spawning (PNMT) phases. Maintenance of the fish under long photoperiods (16L:8D) and high temperature (28 +/- 2 degrees) stimulated the NA and A, and DBH and PNMT activities, and suppressed the DA mechanism, the changes being maximal in the raised temperature groups. In the resting phase (December), ovariectomy (OVX) or estradiol-17 beta (E2) replacement in 4-week ovariectomized fish did not produce any significant effects on the CA and enzyme activities. On the contrary, in the prespawning phase (May), OVX produced differential and biphasic responses on CA and the enzymes. The contents and turnovers of both NA and A increased significantly at 2-5 weeks and decreased in the sixth week. However, the reverse was true for DA. The DBH and PNMT activities (assayed only 3, 4, and 6 weeks after OVX) were elevated significantly in the third and fourth weeks but decreased in the sixth week. Plasma levels of gonadotropin (GTH) increased significantly at all durations of OVX in a bimodal pattern while the E2 levels decreased consistently. Supplementation with a low dose (0.1 microgram/g BW) of E2 restored the NA and A and enzyme activities while the higher doses (0.5, 1.0, and 5.0 micrograms/g BW) depleted them. The reverse was true for DA. The low dose of E2 restored the GTH level while the higher ones inhibited it significantly. These results indicate that both environmental photoperiod and temperature and E2-negative feedback act on the CA to modulate GTH secretion.

Rapid HPLC assay with coulometric detection for norepinephrine and 3-methoxy-4-hydroxyphenylglycol in the mouse brain.

For the rapid assay of norepinephrine (NE) and its major metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG) in the mouse brain, we developed a simple method using isocratic HPLC with coulometric detection. This method permits NE and MHPG assay within 5 min in one chromatographic run. Within-run coefficients of variation for NE and MHPG in the working standard solution were 0.8% and 0.6% (n = 50), respectively. The detector responses were linear from 0.025 to 100 pmol for NE and from 0.05 to 100 pmol for MHPG in the working standard solution. Using this method, the NE and MHPG concentrations were measured in discrete brain areas of the mouse prior treatment with or without alpha-methyl-p-tyrosine or N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4).

A factor(s) from a trophoblast cell line increases tyrosine hydroxylase activity in fetal hypothalamic cell cultures.

We previously reported that a factor(s) from rat choriocarcinoma (Rcho-1) cells suppresses circulating PRL levels and increases tyrosine hydroxylase activity in tuberoinfundibular dopaminergic neurons in vivo. The purposes of this study were to determine whether this factor(s) increases tyrosine hydroxylase activity in fetal hypothalamic cells in vitro and to evaluate its chemical nature. The Rcho-1 cells are of placental origin and have the capacity to differentiate into giant cells and produce members of the placental PRL family. MMQ cells, a pituitary cell line that secretes PRL, and HRP-1, a placental cell line that does not produce any known members of the PRL family, were used as control cells. Tyrosine hydroxylase activity was assessed by incubation of hypothalamic cells for 1 h with 100 microM brocresine, an inhibitor of aromatic L-amino acid decarboxylase. Tyrosine hydroxylase activity was increased in a density-dependent manner when Rcho-1, but not HRP-1 or MMQ, cells were cocultured with hypothalamic cells for 24 h. Control and Rcho-1-stimulated tyrosine hydroxylase activities were markedly reduced with 1 mM alpha-methyl-p-tyrosine, a specific inhibitor of tyrosine hydroxylase. Tyrosine hydroxylase activity was not altered when hypothalamic cells were incubated for 24 h with rat PRL or recombinant rat placental lactogen-I, whereas a 24-h stimulation with 100,000 Rcho-1 cells and a 1-h stimulation with 5 mM (Bu)2cAMP increased tyrosine hydroxylase activity 3.7- and 3-fold, respectively. The magnitudes of the increase in tyrosine hydroxylase activity were similar when hypothalamic cells were cocultured with Rcho-1 cells for 1 and 24 h. Acetic acid extracts of Rcho-1, but not HRP-1 or MMQ, cells increased tyrosine hydroxylase activity within 1 h in a concentration-dependent manner. The 3-fold increase in tyrosine hydroxylase activity observed with 500,000 Rcho-1 cell equivalents was markedly reduced with 1 mM alpha-methyl-p-tyrosine. The mol wt range of the tyrosine hydroxylase-activating factor(s) (THAF) was estimated using ultrafiltration membranes. The majority of activity was found in the eluate from a 1,000 mol wt cut-off membrane. THAF activity in Rcho-1 cell extracts was decreased by preincubation with pronase, a nonspecific proteolytic enzyme, suggesting that the factor(s) is a peptide. THAF was resistant to inactivation by trypsin or chymotrypsin pretreatment. However, both enzymes destroyed the ability of pituitary adenylate cyclase-activating peptide, either alone or with Rcho-1 cell extracts, to increase tyrosine hydroxylase activity. Oxidation of Rcho-1 cell extracts with performic acid abolished THAF activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Age-related changes in biogenic amines, opiate, and steroid receptors in the prepubertal bull calf.

Events leading to the increase in pulsatile LH secretion during prepubertal development in the bull calf may include removal of inhibitory or the development of stimulatory mechanisms affecting the hypothalamic release of GnRH. To examine possible contributing systems, serial blood samples were collected from Holstein bull calves at 2, 5, and 10 wk of age one day prior to receiving either no treatment (controls) or two injections of alpha-methyl-p-tyrosine (alpha-MPT), an inhibitor of catecholamine synthesis. Blood was sampled every 10 min for 5 h and serum was analyzed for LH by RIA. Following treatment, animals were killed and hypothalamic and pituitary tissues were removed for analysis of total opiate receptors, mu-opiate receptors, estrogen and androgen receptors and concentrations of monoamines: dopamine, the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DO-PAC), norepinephrine, serotonin, and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA). Pulses of LH increased from non-detectable at 2 wk to nearly 1.5 pulses per sampling period at 10 wk. Pulse height rose to 0.95 +/- 0.16 ng/ml at 10 wk. Total opiate receptor number as determined by binding to naloxone was unchanged in all tissues between 2 and 10 wk. In contrast, mu-opiate receptors (DAGO binding) increased 2-fold in the preoptic-anterior hypothalamic area between 5 and 10 wk. No age-related changes in estrogen receptor concentrations were observed in any tissue except the anterior pituitary in which binding increased 3.2-fold between 2 and 10 wk. A similar increase was not noted for androgen receptors in the pituitary; however, testosterone binding in the preoptic-anterior hypothalamic area was 4.6-fold higher at 5 wk compared to levels at 2 and 10 wk.(ABSTRACT TRUNCATED AT 250 WORDS)

Synergistic interaction of D1 and D2 dopamine receptors in the modulation of the reinforcing effect of brain stimulation.

Rats were trained to press a bar for hypothalamic stimulation, and a frequency-response function was plotted. Quinpirole (a selective D2 agonist) facilitated self-stimulation when injected alone but failed to show the facilitatory effect when injected either 1 hr before or 1 hr after injection of SCH 23390 (a D1 antagonist). Injection of reserpine followed by alpha-methyl-p-tyrosine virtually eliminated self-stimulation. Subsequent injection of either SKF 38393 (a D1 agonist) alone or quinpirole alone did not restore self-stimulation, but a combination of quinpirole and SKF 38393 did. The results suggest that a D2 dopamine agonist facilitates the reinforcing effect of brain stimulation only if D1 receptors are activated by endogenous dopamine or by an exogenous agonist.

Evidence for the presence of noradrenergic neurons and their inhibitory action on luteinizing hormone-releasing hormone release in cultured fetal rat hypothalamic cells.

The control of LHRH release by catecholamine systems during fetal life (embryonic stages) was studied using hypothalamic neurons in primary cell cultures and an attempt was made to characterize the receptor type involved. Phenylephrine and clonidine, respectively alpha 1 an alpha 2 adrenoreceptor agonists, both inhibited LHRH release. These agonist inhibitory induced-effects were antagonized by the respective alpha 1 and alpha 2 adrenoreceptor antagonists (prazosin and rauwolscine). Both prazosin and rauwolscine applied alone induced a marked increase in LHRH release. Similarly, inhibition of catecholamine synthesis obtained by alpha-methyl-para-tyrosine (alpha-MT) led to a significant increase in LHRH release. The stimulatory effects induced by alpha 1 and alpha 2 adrenoreceptor antagonists or by alpha-MT on LHRH release suggest the presence of noradrenergic and/or adrenergic cells in fetal hypothalamic cultures. Therefore, catecholamine contents were measured in fetal hypothalamic cells in culture. Measurable amounts of norepinephrine and dopamine were found in cells, although epinephrine was undetectable. These results show: 1--noradrenergic cells are present in primary culture of fetal hypothalamic cells. 2--This intrinsic hypothalamic noradrenergic system exerts an inhibitory control on LHRH release at an early stage of development through alpha 1 and alpha 2 adrenoreceptors.

Tyrosine augments dopamine release in stimulated rat retina.

Endogenous dopamine (DA) release was measured in perfused rat retinae. Perfusion with elevated potassium (40 mM K) resulted in a 5-6-fold increase in DA release over baseline or 11.6 +/- 0.9% of final tissue DA content. When the selective DA D2 receptor agonist quinpirole was added to the perfusion medium (at 1 and 10 microM), K-stimulated DA release was significant decreased compared to controls (to 7.0 +/- 1.6 and 6.14 +/- 1.4%, respectively). Addition of the D2 antagonist (+/-)-sulpiride (10 microM) significantly increased DA release to 19.1 +/- 1.3%. DA could be released with successive pulses of K; an initial 10 min pulse resulted in a 4-5-fold increase in endogenous DA release over basal levels or 11.4% of the final retinal tissue DA content and a 3-fold increase (a 9.3% fractional release) upon a second K stimulation given 50 min later. The ratio of stimulated DA release during the two K pulses was 0.82 +/- 0.04. When L-tyrosine (100 microM) was included in the medium throughout the perfusion, K2/K1 was increased to 1.14 +/- 0.13. Both tissue DA level and release were decreased by the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine (AMPT). At 10 microM AMPT K-stimulated DA release was reduced by 50% during the first pulse and completely abolished during the second K pulse. At 100 microM both basal and K-stimulated release were significantly reduced. Exposure of dark-adapted retinae to light in L-tyrosine-supplemented perfusion medium resulted in an increased release of DA compared to retinae perfused with tyrosine-free medium.(ABSTRACT TRUNCATED AT 250 WORDS)