B. Kanyicska

Noradrenergic innervation of the rat hypothalamus: Experimental biochemical and electron microscopic studies

The concentrations of noradrenaline in individual hypothalamic nuclei and in the median eminence were measured 7-10 days following surgical transections of the lower brain stem or electrolytic lesions of the medullary noradrenaline-containing cell groups. Terminal degeneration in the hypothalamus was studied after the same surgical procedures. Direct, monosynaptic connections between the dorsomedial hypothalamic nucleus and all the noradrenaline-containing cell groups investigated were found. Degenerated synaptic boutons were demonstrated in the median eminence, arcuate, dorsomedial, ventromedial, periventricular and paraventricular nuclei following lesions of the solitary tract and of the lateral reticular nucleus. Biochemical measurements indicate that the pontine-medullary noradrenergic cell groups are the source of hypothalamic norepinephrine. Ascending noradrenergic fibers destined to terminate in the hypothalamus are provided by several cell groups, though the bulk of the NA-fibers seem to originate in the A1-group, in the ventrolateral part of the medullary reticular formation. Most of these fibers join the ventral NA bundle, fewer join the dorsal periventricular tract and several probably also join the dorsal NA bundle. A significant overlap was found in the hypothalamic arborization of the noradrenergic fibers, so that no strict topographical organization seems to be present either in their origin or their termination.

Distribution of norepinephrine and dopamine in cerebral cortical areas of the rat

Concentrations of norepinephrine and dopamine were determined using enzyme isotope assay in 27 microdissected cerebral cortical areas of the rat. A detailed map is presented for microdissection of rat cerebral cortex. Norepinephrine was found in low but still measurable quantities throughout the cortex. Differences between cortical areas are also low. Relatively highest levels were demonstrated in the pyriform, insular and entorhinal cortices. The distribution of dopamine was found to be uneven with a maximal regional difference of 1:24. Concentration of dopamine was in all areas lower than that of norepinephrine. The highest dopamine concentration (2,4 ng/mg protein) was measured in the rostral pyriform cortex but other mesocortical (cingulate, frontal, insular and entorhinal) dopaminergic areas also contained relatively high amounts. Except for the caudal occipital and caudal entorhinal cortices all regions studied contained measurable quantities of dopamine. Its low concentration relative to norepinephrine (below 15%) suggests that in the cortical areas studied dopamine is present as the precursor of norepinephrine.

Simultaneous radioenzymatic assay of catecholamines and dihydroxy-phenylacetic acid /DOPAC/; comparison of the effects of drugs on the tuberoinfundibular and striatal dopamine metabolism and on plasma prolactin level

Abstract A simultaneous radioenzymatic assay for catecholamines and DOPAC has been developed. 3 H-Methoxy amines and 3 H-homovanillic acid formed in the presence of 3 H-S-adenosyl-methionine and catechol-O-methyl transferase were separated by organic solvent extraction and chromatography. Chlorpromazine, haloperidol, but not sulpiride increased the DOPAC content in the striatum, without affecting the DOPAC level in the median eminence. γ-Butyrolactone increased the dopamine content also only in the striatum. The monoamine oxidase inhibitor pargyline decreased the DOPAC level in both areas examined. All the substances employed increased plasma prolactin level. The biochemical responses of nigrostriatal and tubero-infundibular dopaminergic neurons may not be analogous.

Adrenergic innervation of the rat hypothalamus

The adrenergic innervation of the hypothalamus was studied by measuring hypothalamic adrenaline levels following surgical transection of the lower brain stem or electrolytic lesion of the medullary adrenaline-containing cell groups. The adrenaline levels in some hypothalamic nuclei and in the median eminence showed a slight decrease after partial transection of the medulla oblongata, whilst there was a pronounced decrease (by 59-78%) 7-10 days following total hemisection or unilateral lesion of the C1-catecholaminergic cell group in the medulla oblongata.

Catecholamine concentration of various brain nuclei of the rat as affected by ACTH and corticosterone.

The acute effect of ACTH and corticosterone on catecholamine concentration of individual brain nuclei has been examined. ACTH significantly increased the noradrenaline (NA) content in the locus coeruleus, and decreased it in the ventromedial and arcuate nuclei. No change was observed after ACTH in the dopamine (DA) concentrations of the mentioned areas and in the catecholamine level of the mamillary body, hippocampus, medial habenular nucleus and of the pituitary. Corticosterone increased the NA content of the supraoptic nucleus and the NA and DA levels in the median eminence, while it did not affect the amine concentrations in the locus coeruleus.

Prolactin release induced by opiate agonists, effect of glucocorticoid pretreatment in intact and adrenalectomized rats

Cortisol administered at a dose of 25 mg/kg 24 h before measurements decreased the prolactin secretion induced by intraventricularly given opioids (dynorphin, beta-endorphin, Met-enkephalin or D-Met-Pro-enkephalinamide). The effect of cortisol was depressed by actinomycin D pretreatment. The cortisol-induced inhibition of the action of morphine was facilitated in adrenalectomized animals; measuring the effects of increasing doses of cortisol a maximal inhibition was obtained at a dose of 5 mg/kg. The opioid-induced corticosterone secretion was not affected 24 h after a single administration of cortisol. The present results show that the cortisol-induced inhibition of opioid-induced prolactin secretion is dependent on protein synthesis and independent of changes in drug metabolism, and of the type of opiate receptor preferentially affected by the opiate agonists employed.

Lack of Correlation between Hypothalamic Serotonin and the Ether-Induced ACTH Secretion in Adrenalectomized Rats

The central serotonergic system was manipulated using a serotonin receptor antagonist (cyproheptadine), electrolytic lesioning of the raphe nuclei and neurochemical destruction of the serotonergic terminals in the hypothalamus. The effects of these interventions on ether-induced ACTH secretion were studied in adrenalectomized rats. Serotonin, norepinephrine and dopamine concentrations were measured in the medial basal hypothalamus (MBH) or in individual nuclei of the hypothalamus and of certain midbrain regions. Cyproheptadine pretreatment inhibited ether-induced ACTH hypersecretion in adrenalectomized animals. Neither the electrolytic lesions of the midbrain raphe nuclei, nor the neurotoxic destruction of the hypothalamic serotonergic terminals (by intraventricular administration of 5,6-dihydroxytryptamine) caused any alteration of stimulated ACTH secretion after ether inhalation and/or long-term corticoid deficiency. These results suggest a lack of correlation between the activity of the central serotonergic system and the ACTH releasing effect of ether-stress in adrenalectomized rats.

Diurnal Variation in Prolactin, Adrenocorticotropin and Corticosterone Release Induced by Opiate Agonists in Intact and Adrenalectomized Rats

Diurnal variations of the effectivity of beta-endorphin (beta-End), dynorphin (DYN), Met-enkephalin (Met-Enk), D-Met2-Pro5-enkephalinamide (D-Met-Pro-Enk) and morphine to induce prolactin (PRL) and adrenocorticotropin (ACTH)/corticosterone (CS) release in intact and adrenalectomized rats have been examined. The response to morphine (10 mg/kg s.c.), Met-Enk (200 micrograms/rat i.c.v.) and D-Met-Pro-Enk (0.5 microgram/rat i.c.v.) did not change with different times of the day, while that to beta-End (0.5 microgram/rat i.c.v.), DYN (1 microgram/rat i.c.v.) and U50-488H, a selective kappa agonist (10 mg/kg s.c.), showed a circadian rhythm in stimulating PRL release, with a higher increase in the afternoon (16.00-17.00 h) than in the morning (08.00-09.00 h). In adrenalectomized rats the loss of this circadian rhythm was shown. The CS release evoked by morphine, D-Met-Pro-Enk, Met-Enk and DYN was demonstrable only in the morning when the basal CS level was significantly lower than in the afternoon. The afternoon release of ACTH by morphine was higher than in the morning in adrenalectomized rats. beta-End and U50-488H were equally active in the morning and in the afternoon in increasing CS secretion. The present results suggest that the diurnal rhythm in the response of CS and PRL release to opioids is in relation with the glucocorticoid secretion.

Potent GnRH agonists containing L-amino acid derivatives in the six position

New agonists related to gonadotropin-releasing hormone (GnRH) have been synthesized that are comparable in potency to the GnRH and its superagonists for release of LH and estrus suppression without substitutions with D- or unnatural amino acids in position 6. We now report a series of L-beta-aspartyl-6 GnRH analogs containing only naturally occurring L-amino acids in the whole sequence, exhibiting considerable in vivo biological activity. Dose and time dependent LH release capability of the different analogs in adult male mice, estrus suppression comparisons and blockade of ovulation in female rats are given. The incorporation of L-Asp-OMe and L-Asp-OBzl in position 6 of GnRH resulted in the most potent GnRH agonists (to 12-20xGnRH potency) in this series inducing a biphasic biological response similar to the D-amino acid-6 substituted superactive GnRH analogs. A correlation between the LH releasing potencies of the analogs and their HPLC retention times was also investigated. Peptide synthesis were achieved using either solid phase or solution phase methodology.

Effect of chronic morphine treatment on the adrenaline biosynthesis in adrenals and brain regions of the rat

Phenylethanolamine-N-methyltransferase (PNMT) activity and tissue catecholamine content were examined after 13 days morphine treatment. Prolonged morphine treatment did not alter the PNMT activity in brain regions (A1/C1 and A2/C2 cell groups, medial basal hypothalamus, median eminence). However, the enzyme activity and the adrenaline content were increased in the adrenal medulla of male rats. In parallel, morphine treatment induced adrenal hypertrophy. In female or hypophysectomized male animals the chronic morphine treatment had no effect on adrenal weight but evoked the increase of PNMT activity. It is concluded that the morphine-induced increased adrenaline biosynthesis in the adrenal gland is not fully dependent on the intact pituitary-adrenal axis and may be mediated partly by a neural mechanism (increased splanchnic nerve activity) or by a direct effect of morphine.