Behaviorally equivalent stressors differentially modify the monoamine altering property of d-amphetamine

Behavioral and endocrine change following chronic predatory stress

Adult male rats showed very high levels of crouching when exposed to a cat, with suppression of the nondefensive behaviors (e.g., lying, locomotion, rearing) that were shown by toy cat-exposed controls. The crouching of cat-exposed rats declined slightly but reliably with increasing time within daily 60-min exposure sessions. However, the lack of a reliable cat-exposure x days interaction for crouching over the 20 days of testing indicated minimal habituation of the rats' defensive response to the cat over this exposure schedule, although rat and cat were separated by a wire mesh screen, precluding contact and pain. Following the 20th day of exposure, cat-exposed rats showed reliably higher basal plasma corticosterone levels, suggesting a lack of habituation of this stress-linked response as well. Adrenal weights were also higher and thymus weights lower in these animals compared with controls, while spleen and testes weights and testosterone levels were not reliably different. Of the 13 cat-exposed subjects, 6 (and a single control) failed to show a 10 microg/mL corticosterone (CORT) increase in response to an acute restraint stressor. In 3 of these 6 cat-exposed rats, the failure to meet this criterion was attributable to a low level of CORT following restraint, suggesting failure of the normal CORT surge to the acute restraint stressor. These findings of organ weight changes, enhanced basal CORT, and reduced CORT response to stress in a subgroup of animals are similar to many of the phenomena obtained with other intense, chronic stressors such as subordination, and suggest that repeated predator exposure produces a pattern of intense behavioral and endocrine response that is very slow to habituate. Because it is a natural stressor for both male and female subjects, and one for which pain and even handling of the subject is unnecessary, cat exposure may provide a particularly relevant and adaptable paradigm for research involving analysis of gender effects on the stress response.

Effect of reserpine on the brain uptake of carbon 11 methamphetamine and its N-propagyl derivative, deprenyl

The enantiomers of methamphetamine (MAMP) and its N-propagyl derivative, deprenyl, were labelled with carbon 11, and the tissue distribution of these labelled compounds in mice was studied. Both enantiomers of 11C-MAMP rapidly entered into the brain and then disappeared according to a single exponential curve. The enantiomers of 11C-deprenyl were also rapidly distributed to various organs in the same manner. With regard to elimination, however, a stereoselective, long-term retention of radioactivity in the brain, heart and lung, due to its irreversible binding with monoamine oxidase B, was observed for L-11C-deprenyl. In reserpinized mice, the initial brain uptake of both the L and D forms of 11C-MAMP was significantly decreased. On the other hand, the brain uptake of both enantiomers of 11C-deprenyl was slightly increased by pretreatment with reserpine. A significant and non-stereoselective elevation of the lung uptake of 11C-deprenyl was also seen in reserpinized mice. In addition, both the relative tissue distribution and ratios of radioactivity in the brain compared with blood or heart at 1 and 5 min after the injection of 11C-labelled methanol in mice were not changed by reserpine. These results indicate that the transport or binding processes of these amines rather than the blood flow might be altered by reserpine. There would be an important role of the pKa values of amines in both processes. The reduction of brain uptake as well as the change in ratio between brain and heart of L-11C-MAMP in reserpinized mice 1 min after injection were reversed by treatment with amphetamine in a dose-related manner.(ABSTRACT TRUNCATED AT 250 WORDS)