EFFECTS OF SEQUENTIAL REMOVAL OF RATS FROM A GROUP CAGE, AND OF INDIVIDUAL HOUSING OF RATS, ON SUBSTANCE-P, CHOLECYSTOKININ AND SOMATOSTATIN LEVELS IN THE PERIAQUEDUCTAL GRAY AND LIMBIC REGIONS

The effect of specific stressful stimuli on neuropeptide levels was st udied in rat brain regions known to be involved in the mediation of st ress responses and anxiety. Rats were sequentially removed, one by one with 20-min intervals from group cages and immediately decapitated. A selective increase of the somatostatin level was observed in the amyg dala in the rats taken for sacrifice second last and last, compared to the rats taken earlier from the respective group cage (increases by 4 0 to 69%, p < 0.05 or p < 0.01). Isolation of rats in single cages for 24 h or 1 week before sacrifice, increased the substance P level in t he dorsal periaqueductal grey by 26 and 27% (p < 0.05 in both cases), respectively, compared to group housed rats. In group housed rats trea ted with diazepam (5 mg/kg, s.c.) 140 min before sacrifice, the level of substance P in the rostral hippocampus and dorsal periaqueductal gr ey was reduced by 40% (p < 0.001) and 28% (p < 0.05), respectively, co mpared to saline treated controls. In conclusion, handling, as well as a single dose of the anxiolytic drug diazepam, appears to induce rapi d, selective and region-specific changes of regional brain peptide lev els in the rat. The effects of handling are likely to be related to th e acute stress response and are probably not secondary to increased pl asma glucocorticoid levels.