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Beta‐adrenergic signal transduction in the hypothalamus of the European hamster: Relation with the seasonal hibernation cycle and the diurnal activity cycle
Author(s) -
Pleschka Klaus,
Nürnberger Frank
Publication year - 1997
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1016/s0248-4900(98)80008-7
Subject(s) - hibernation (computing) , medicine , biology , endocrinology , forskolin , hypothalamus , photoperiodism , stimulation , adrenergic , circadian rhythm , adenylyl cyclase , torpor , hamster , receptor , thermoregulation , biochemistry , botany , state (computer science) , algorithm , computer science
Mammalian hibernation, an adaptation to survive harsh winter conditions, is one of the most prominent seasonal rhythmic processes exactly regulated on a low metabolic level. Diurnal variations in vegetative physiology are missing during hibernation; however, a precisely working diurnal system is mandatory for both the proper initiation and termination of the annual hibernation phase and the periodical arousal reactions. Biorhythms and the vegetative physiological processes connected with hibernation are, among others, controlled by hypothalamic noradrenaline systems. In this study, the density, binding capacity, and relative proportions of β 1 ‐ and β 2 ‐adrenergic receptors (AR) within the hypothalamus of: 1) motorically inactive summer; 2) motorically active summer; 3) aroused, motorically active winter; and 4) deeply hibernating winter European hamsters ( Cricetus cricetus ) were studied. For further analysis of the β‐adrenergic signal transduction cascade, the activity of adenylyl cyclase (AC) was measured by formation of cAMP in controls, after stimulation of G proteins, or after forskolin stimulation without or in presence of manganese ions. While β 1 ‐ and β 2 ‐AR subtypes were nearly equally abundant (50% β 1 :50% β 2 ) in active summer, inactive summer, and hibernating hamsters, a significant redistribution in favor of β 2 ‐AR occurred after arousal (40% β 1 :60% β 2 ). The activity of AC was much higher in active summer hamsters than in inactive summer, aroused winter, and hibernating winter hamsters. When AC was stimulated by guanylylimidophosphate [Gpp(NH)p], MnCl 2 , forskolin, or by forskolin in presence of MnCl 2 instead of MgCl 2 , the potency to stimulate AC was found to show the following rank order: basal < Gpp(NH) p < MnCl 2 ≤ forskolin + MnCl 2 < forskolin.