UP-REGULATION OF NICOTINIC RECEPTORS FOLLOWING CONTINUOUS-INFUSION OFNICOTINE IS BRAIN-REGION-SPECIFIC

Rats receiving 4 mg nicotine/kg/day via implanted minipumps sustained plasma nicotine concentrations of 40 ng/ml throughout two weeks of nic otine infusion. Numbers of brain [H-3]nicotine binding sites were incr eased by about 50% in cortex and hippocampus whereas numbers of [H-3]n icotine binding sites in striatum were unaffected by nicotine treatmen t at either of the timepoints examined (7, 14 days). Cortical [I-125]a lpha-bungarotoxin and [H-3]QNB binding sites were also unchanged. The regional selectivity of nicotinic receptor modulation may reflect the low dose of nicotine used and the mode of administration. The changes observed may be pertinent to the continuous administration of nicotine in man, via transdermal nicotine patches.