Chronic subordination stress in male tree shrews: Replacement of testosterone affects behavior and central alpha(2)-adrenoceptors

G. Flugge et al., Chronic subordination stress in male tree shrews: Replacement of testosterone affects behavior and central alpha(2)-adrenoceptors, PHYSL BEHAV, 73(3), 2001, pp. 293-300
Citations number
Categorie Soggetti
Psycology,"Neurosciences & Behavoir
Journal title
ISSN journal
0031-9384 → ACNP
Year of publication
293 - 300
SICI code
Subordination stress induced by social defeat in male animals is known to i nhibit gonadal functions and it has been discussed whether the resulting de ficit in testosterone might play a role in subordination behavior. One of t he major transmitter systems involved in regulation of behavior is the nora drenergic system. To analyze whether a testosterone replacement can alter s ubordination behavior and whether this might be related to changes in the b rain noradrenergic system, we quantified alpha(2)-adrenoceptors (alpha(2)-A Rs) in the central nervous system of male tree shrews. Animals were submitt ed to chronic subordination stress and received testosterone at the same ti me. Behavior was monitored during all phases of the experiment: the control period of 10 days, the period of social stress lasting 10 days when subord inates were confronted daily with a dominant male, and, subsequently, the s tress and treatment period of 18 days when in parallel to the stress, anima ls received either injections of testosterone or vehicle. Brain alpha2-ARs were quantified by in vitro receptor autoradiography using the antagonist l igand H-3-RX821002. Locomotor activity decreased significantly during the s tress period and was not re-normalized by testosterone. In contrast, testos terone re-normalized scent marking behavior and autogrooming, parameters th at had both been reduced due to the subordination stress. Vehicle injection s improved none of these behaviors. In 8 of 10 brain regions that were anal yzed, numbers of alpha(2)-adrenergic binding sites were increased in stress ed animals that received vehicle injections, but a difference between testo sterone and vehicle injected animals was only observed in five regions. The se brain regions are all known to be involved in emotional behavior (anteri or hypothalamus, medial nucleus of the amygdala, cingulate cortex) or auton omic regulation, respectively (solitary tract nucleus, dorsal motor nucleus of vagus). Therefore, our data show that testosterone influences behavior of male subordinates and modulates alpha(2)-AR expression in their brains. Androgen-mediated alterations in receptors occur in brain regions that are known to be involved in emotionality, e.g., in the anterior hypothalamus wh ich regulates aggressive behavior. One can therefore conclude that alpha2-A Rs contribute to neuronal functions that are responsible for subordination of stress behavior, and that testosterone-induced receptor changes are rela ted to the partial restoration of normal behavior. (C) 2001 Elsevier Scienc e Inc. All rights reserved.