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Biomedical subjects

C Beyer

Publications and source records attributed to C Beyer.

At least 199 records · Page 11Linked to original sources
PubMed1977

In vitro conversion of 5-androstenediol to testosterone by the central nervous system and pituitary of the male rat.

The in vitro metabolism of 7-3H-5-androstenediol by the pituitary, some brain structures, and ventral prostate of adult castrated male rat was studied. Conversion of 5-androstenediol to radiochemically pure testosterone was demonstrated in all tissues studied in the presence of a NADPH generating system. Formation of dihydrotestosterone and dehydroepiandrosterone was also detected. The higher conversion rates were found in the pituitary, hypothalamus and mesencephalic tegmentum. These results demonstrate the presence of 3beta-hydroxy steroid oxidoreductase, delta4- delta5 isomerase, 5alpha-reductase, and 17beta-ol dehydrogenase in the rat brain which may in part explain the behavioral and brain virilization effects of 5-androstenediol.

Androstenediol↗
PubMed1976

Changes in multiunit activity and EEG induced by the administration of natural progestins to flaxedil immobilized cats.

The effects of progesterone (P) and 7 of its metabolites on the EEG and multiunit activity (MUA) of various limbic structures were studied in flaxedil immobilized cats. Most progestins inhibited the MUA of the mesencephalic reticular formation, hippocampus and hypothalamus and induced cortical EEG synchronization. MUA changes in the mesencephalic reticular formation frequently preceded EEG synchronization. Progestins reduced in the 5 beta postition (pregnanolone, epipregnanolone and pregnanedion) inhibited neuronal discharge and synchronized EEG activity with shorter latencies and in lower doses than those reduced in the 5 alpha position (allopregnanolone and allopregnanedion). Progestins having the delta 4,3-keto structure (P, 20 alpha-hydroxy pregnenone, 20 beta-hydroxy pregnenone) induced electrophysiological changes with prolonged latencies and in doses significantly higher than ring A reduced progestins. Administration of epipregnanolone to "cerveau isole" preparations depressed neuronal firing in those structures located rostral to the level of the brain stem transection (hypothalamus, hippocampus), but failed to increase the already synchronized cortical activity. These results suggest that: a, ring A reduction increases the capacity of P and other delta 4,3-keto progestins to inhibit neuronal discharge in certain brain areas and b, changes in neuronal firing induced by progestins are not necessarily mediated through the cat brain stem reticular formation.

Animals↗
PubMed1975

Analysis of various factors involved in EEG synchronization during milk drinking in the cat.

Electroencephalographic (EEG) and multineuronal activity (MUA) from several brain structures were recorded in 11 adult cats during milk drinking. Milk drinking elicited parietal and hippocampal EEG synchronization and inhibited multiunit discharge in several brain regions. The proportion of EEG synchronization varied considerably between animals, but remained more or less constant for each cat after several testing days. Neither modification of milk concentration nor fasting influenced the proportions of EEG synchronization during milk drinking. Adaptation of the animals to the experimental environment facilitated the appearance of EEG synchronization during milk drinking. Chlorpromazine (3 mg/kg) significantly increased the proportion of EEG synchronization observed during milk drinking. By contrast, displacement of the head, neck or postural body adjustments during milk drinking blocked EEG synchronization. Amphetamine also had a suppressive effect on the EEG parietal and hippocampal synchronic activity observed during milk drinking. Our results suggest that development of parietal EEG synchronization in response to pleasant stimulation is a complex phenomenon requiring a relaxed condition of the animal, including its adaptation to the experimental environment and relative immobility with the concomitant diminution of afferent inflow from some of the muscles involved in locomotion.

Amphetamine↗
PubMed1975

In vitro metabolism of 3-H-androstenedione by the male rat pituitary, hypothalamus, and hippocampus.

The in vitro metabolism of 2,2-3-H-androstenedione by the pituitary, hypothalamus, and hippocampus of intact and castrated adult male rats was studied. Conversion of androstenedione to radiochemically pure 5alpha-androstanedione, testosterone, 5alpha-dihydrotestosterone, androsterone, and traces of 3alpha, 5alpha-androstanediol was demonstrated in minced preparations of the three tissues in the absence of cofactors. 5alpha-androstanedione was the metabolite formed in the highest proportion. The pituitary showed the highest enzymatic conversions followed in decreasing order by the hippocampus and the hypothalamus. Castration performed three weeks prior to the experiments resulted in a significant decrease of pituitary 17beta-old-dehydrogenase activity with a concomitant increase of 5alpha-reductase. No significant changes were observed after castration in the hypothalamus and the hippocampus.

Androstenedione↗