Behavioral and hormonal effects of centrally injected "anxiogenic" neuropeptides in growing pigs

Records of behavior (alertness, posture, ore-nasal responses, activity leve l, and vocalization pattern) were made in prepubertal pigs (n = 6) during a 60-min period following central injections of equimolar (21 nmol) doses of porcine CRH (pCRH), urocortin (UCN), actadecaneuropeptide (ODN), or saline vehicle (SAL). Blood samples were also collected at 15-min intervals befor e, during, and after the test, and used to determine plasma cortisol, prola ctin, and growth hormone concentrations. The pigs became excited and highly active after pCRH, and to a lesser extent following UCN administration, bu t were subdued when given ODN or SAL. None of the peptides significantly af fected prolactin or growth hormone release, but both UCN, and especially pC RH, increased cortisol concentrations. The emotional responses induced by p CRH and UCN are consistent with observations in rodents, which indicate tha t centrally administered CRH-like peptides have anxiogenic effects. In cont rast, ODN, which inhibits benzodiazepine binding at the GABA, receptor and is anxiogenic in rodents, lowered plasma cortisol and had no overt behavior al effects. Hence, at the dose administered, there was no evidence to indic ate that ODN acted as an anxiogen in this species. (C) 1999 Elsevier Scienc e Inc.