The habituation of brainstem catecholaminergic groups to chronic daily restraint stress is stress specific like that of the hypothalamo-pituitary-adrenal axis.

It has previously been shown that immobilization and ether stress induce activation of the hypothalamo-pituitary-adrenal (HPA) axis and that this activation occurs subsequent to activation of brain stem catecholaminergic neurones. In the present study we have investigated whether the brain stem catecholaminergic (CA) neurons show habituation to chronic daily intermittent exposure to the same restraint stress comparable to that of the HPA axis. The level of activity of the brainstem CA groups was estimated by measurement in tissue punches of content of 3,4-dihydroxyphenylacetic acid (DOPAC), a side metabolite of noradrenaline and adrenaline biosynthesis which has been shown to be a reliable index of the stress-induced activation of the CA groups. The level of activity of the HPA axis was determined by measurement of plasma corticosterone and adrenocorticotropic hormone (ACTH) levels. The animals were submitted to a 15 min restraint stress daily. They were sacrificed at the end of the stress session on day 3, 5 and 10. The ACTH response to the acute restraint stress whilst unchanged on day 3 was significantly decreased on day 5 (-54%) and day 10 (-70%) compared to the response in naive rats. The approximately twofold increase in DOPAC level induced by acute restraint stress in the so-called CA medullary group A1/C1 of naive rats was reduced in daily restraint rats on day 5 (-22%) and day 10 (-30%) but was unchanged on day 3. A small (-20%) decrease of the stress-induced DOPAC response in the A2/C2 CA group and locus coeruleus was also observed on day 10.(ABSTRACT TRUNCATED AT 250 WORDS)