Biomedical subjects

K Nikolics

Publications and source records attributed to K Nikolics.

76 records · Page 5Linked to original sources

PubMedDate not supplied

GnRH-prohormone-containing neurons in the primate brain: immunostaining for the GnRH-associated peptide.

The structure of the prohormone for mammalian gonadotropin releasing hormone (proGnRH) includes the GnRH decapeptide followed by a 56 amino acid GnRH-associated peptide (GAP). In this study, we compared immunostaining of brain neurons and fibers for GAP and GnRH in fetal rhesus monkeys and juvenile baboons. We used antisera against different portions of human and rat GAP (proGnRH 14-24, proGnRH 40-53, and proGnRH 52-66) or against GnRH and the PAP technique. Liquid phase absorption with GAP or GnRH confirmed the specificity of these antisera. Major accumulations of GAP immunoreactive (GAP+) perikarya occurred in the medial septal and preoptic areas and the nucleus of the diagonal band of Broca (44.6% in rhesus, 49.6% in baboon), supraoptic region including the area dorsal to the optic tract (21.9% in rhesus, 23.0% in baboon), and the medial basal hypothalamus (15.7% in rhesus, 16.4% in baboon), especially at the infundibular lip. Occasional cell bodies were scattered throughout the hypothalamic and forebrain regions studied. GAP+ fibers were widely distributed, but formed well-defined pathways such as the periventricular and ventral hypothalamic tract. In addition, GAP+ nerve terminals with various densities occurred in the lamina terminalis, the zona externa of the infundibulum, and behind the infundibular stalk. Fetal rhesus macaques had more GAP+ cell bodies, denser fiber networks, and more distinct pathways than juvenile baboons. However, fiber and terminal immunostaining was somewhat less intense for GAP than GnRH in comparable regions. These results indicate that proGnRH (GAP) is present in the same population of neurons as GnRH in the primate brain. They also suggest that post-translational products of proGnRH are present in perikarya, axons and terminals, and that GnRH and GAP and/or further cleavage products are consecreted into hypophysial portal blood in the primate.

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PubMedDate not supplied

Distribution of 3H-alpha-MSH in rat brain.

Radioactive synthetic alpha-MSH, prepared by selective tritiation of its dibromo-L-tyrosine-derivative, was injected into the carotid artery of intact, hypophysectomized or pinealectomized rats. More radioactivity was found in the occipital cortex, cerebellum, and pons-medulla than in most other brain parts of rats decapitated 15 sec and, to a less significant extent, 30 min after injection. Part of this radioactivity behaved like alpha-MSH in several identification procedures. After administration of 3H-tyrosine, the least radioactivity was consistently found in the pons-medulla. Large amounts of radioactivity after 3H-alpha-MSH were found in the pituitary and, particularly in the hypophysectomized rats, in the pineal. The half-time disappearance of the first component of radioactivity from the blood of each group of rats injected with tritiated-alpha-MSH was no more than 2.5 minutes, a time considerably shorter than the behavioral and EEG effects of this pituitary hormone on visual attention.

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PubMedDate not supplied

A prolactin-inhibiting factor within the precursor for human gonadotropin-releasing hormone.

The cloned complementary DNA sequence encoding the human gonadotropin-releasing hormone (GnRH) precursor protein was used to construct an expression vector for the bacterial synthesis of the 56-amino acid GnRH-associated peptide (GAP). GAP was found to be a potent inhibitor of prolactin secretion and to stimulate the release of gonadotropins in rat pituitary cell cultures. Active immunization with peptides corresponding to GAP sequences led to greatly increased prolactin secretion in rabbits.

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PubMedDate not supplied

Immunocytochemical localization in rat brain of a prolactin release-inhibiting sequence of gonadotropin-releasing hormone prohormone.

The structure of a precursor protein for gonadotropin-releasing hormone (GnRH) of relative molecular mass 10,000 has recently been deduced from cloned complementary DNA sequences derived from human placental messenger RNA. The 56-amino-acid peptide representing residues 14-69 of this prohormone exhibits potent inhibition of prolactin secretion. To investigate whether the same prohormone is synthesized in mammalian brain and describe the anatomical distribution of the prolactin-inhibiting region of this molecule, we have generated antiserum to a synthetic peptide containing residues 40-53 of the human placental precursor. We report here that a substance recognized by this antibody is present in GnRH-containing neurones of the rat brain and appears to coexist with GnRH in secretory granules of nerve terminals in the median eminence. These results indicate homology between hypothalamic and placental prohormones for GnRH and are consistent with the suggestion elsewhere in this issue that a prolactin-inhibiting factor (PIF) is generated from this prohormone and cosecreted with GnRH by nerve terminals in the median eminence.

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