Da. Coryslechta et al., NUCLEUS-ACCUMBENS DOPAMINERGIC MEDICATION OF FIXED-INTERVAL SCHEDULE-CONTROLLED BEHAVIOR AND ITS MODULATION BY LOW-LEVEL LEAD-EXPOSURE, The Journal of pharmacology and experimental therapeutics, 286(2), 1998, pp. 794-805
To examine the assertion that changes in nucleus accumbens (NAC) dopam
ine (DA) activity serve as a mechanism of lead (Pb)-induced disruption
of fixed interval (FI) schedule-controlled behavior, the effects of i
ntra-NAC administration of the irreversible DA antagonist EEDQ (N-etho
xycarbonyl-2-ethoxy-1,2-dihyroquinoline) and of dopamine itself on FI
performance were compared in rats that had been chronically exposed to
0, 50 or 500 ppm Pb acetate in drinking water from weaning. Pb exposu
re per se (500 ppm), as in past studies, increased Fl response rates,
primarily by shortening interresponse times. Although DA, which produc
ed rate-dependent effects, increased FI rates at low doses in the 0 an
d 50 ppm groups, it did so by decreasing postreinforcement pause times
. Ail DA doses decreased rates in the 500 ppm group. In contrast, the
DA antagonist EEDQ suppressed FI response rates, effects that were not
strongly rate dependent, by increasing both postreinforcement pause v
alues and mean interresponse times. Pb exposure (500 ppm) delayed the
recovery of response rates to control levels at the highest EEDQ dose,
raising the possibility of a delay in receptor production rate. Colle
ctively, these data suggest that NAC DA activity may be an important m
odulator of FI response rates. Enhanced NAC DA activity may contribute
to Pb-associated increases in FI rates and may underlie the different
ial response of control and 500 ppm Pb-treated groups to intra-NAC DA
administration. The different processes by which DA and Pb increase Fl
rates, however, suggests that additional mechanisms are operative in
the case of Pb.