Attenuation of behavioral consequences of immobilization stress by intra-hippocampal microinjection of zimelidine

ABSTRACT

To investigate the role of hippocampal 5-HT neurotransmission on adaptation to aversive events, individually housed male Wistar rats (200-250 g) were immobilized for 2 h and tested 24 h later in an elevated plus-maze. Immediately after the restraint period they received bilateral microinjections into the dorsal hippocampus of either saline (0.5 microliters) or the nonselective 5-HT1 antagonist dl-propranolol (20 nmol/0.5 microliters). In a second experiment the first microinjection of saline or dl-propranolol was followed by a second microinjection of saline (0.5 microliters) or the 5-HT reuptake blocker zimelidine (20 nmol/0.5 microliters). Although dl-propranolol alone did not change exploration of the elevated plus-maze, it antagonized the increase in the percentage of open arm entries induced by zimelidine (26.0 +/- 4.1 vs 5.64 +/- 3.7 in controls). These results are compatible with the view that post-synaptic 5-HT1a receptors in the hippocampus mediate adaptive or coping responses to aversive events