DIFFERENTIAL-EFFECTS OF NEONATAL HANDLING ON ANXIETY, CORTICOSTERONE RESPONSE TO STRESS, AND HIPPOCAMPAL GLUCOCORTICOID AND SEROTONIN (5-HT)(2A) RECEPTORS IN LEWIS RATS

Neonatal handling (during the first 3 weeks of age) has been reported by others to diminish the hypothalamo-pituitary-adrenal (HPA) responsi vity to stress in adult Long Evans rats, an effect involving a seroton in (5-HT)(2A) receptor-mediated increase in glucocorticoid receptor (G R) gene expression in the frontal cortex and the hippocampus. In addit ion, handled animals may also display enduring reductions in anxiety-r elated behaviours, including in the elevated plus-maze. We have thus a nalysed the aforementioned neuroendocrine and behavioural consequences of neonatal stress in male and female adult Lewis rats, a strain char acterised by its high anxiety and its hyporesponsive HPA axis. Plasma corticosterone, but not behavioural, responses to an elevated plus-maz e test were decreased in handled rats. Besides, hippocampal mineraloco rticoid receptor (MR) and GR binding capacities were not different bet ween handled and non-handled Lewis rats, an observation which could be extended to our adult Long Evans rats. Lastly, neither hippocampal no r cortical 5-HT2A receptor binding capacities in adult Lewis rats were affected by prior handling. In keeping with the failure to detect ear ly handling-induced increases in hippocampal CR binding in 3-week old Lewis and Long Evans rats, the present study reinforces past findings indicating that environmental and genetic factors are crucial variable s in the neonatal handling paradigm. (C) 1998 Elsevier Science Ltd. Al l rights reserved.