Induction of NGFI-B mRNA following contextual fear conditioning and its blockade by diazepam

Expression of the immediate-early gene, NGFI-B (nerve growth factor inducib le gene B), was examined in the amygdala, hippocampus, and neocortex follow ing contextual fear conditioning. Rats were either handled, placed within t he testing context without receiving the footshock, received a footshock im mediately upon placement within the context, or received a footshock after a 3-min delay (delayed-shock). Only the delayed-shock group displayed a fea r response (freezing) in the post-shock period and in a retention test 24 h after fear conditioning. Expression of NGFI-B mRNA was increased in the do rsolateral part of the lateral nucleus of the amygdala (LaDL) and the neoco rtex 30 min following conditioning in the delayed-shock group compared to t he other three groups. In addition, following a retention test conducted 34 h after fear conditioning, NGFI-B mRNA expression was increased in the neo cortex of the delayed-shock group compared to the handled group. In a subse quent experiment, the effects of pretreatment with the anxiolytic drug, dia zepam, on fear conditioning and the concomitant increases in NGFI-B mRNA we re investigated. Rats administered a 2.5 mg/kg, i.p, dose of diazepam befor e fear conditioning did not acquire contextual fear as demonstrated by a la ck of freezing in a retention test. Although diazepam blocked fear conditio ning while the 40% propylene glycol, 10% ethanol vehicle solution did not, both diazepam and the vehicle reduced the conditioning-induced increase in NGFI-B expression in the LaDL. In contrast, the fear-conditioning-induced N GFI-B increase in the neocortex was blocked by diazepam, but not by the veh icle. The data suggest that the transcriptional factor NGFI-B in the LaDL a nd neocortex may play a Functional role in learning and memory of contextua l fear, but blocking the increase in NGFI-B expression in the LaDL is not e ssential for diazepam to interfere with fear conditioning. (C) 2000 Elsevie r Science B.V. All rights reserved.