Autoregulation of dopamine synthesis in subregions of the rat nucleus accumbens

The discovery of a core-shell dichotomy within the nucleus accumbens has op ened new lines of investigation into the neuronal basis of psychiatric diso rders and drug dependence. In the present study, the autoregulation of dopa mine synthesis in subdivisions of the rat nucleus accumbens was examined. W e measured the accumulation of L-3,4-dihydroxyphenylalanine (DOPA) after th e inhibition of aromatic L-amino acid decarboxylase with 3-hydroxylbenzylhy drazine (NSD-1015, 100 mg kg(-1)) as an in vivo index of dopamine synthesis . The effect of the dopamine D-1/D-2 receptor agonist apomorphine (0, 0, 10 0, 500 mug kg(-1)) and the dopamine D-2/D-3 receptor agonist quinpirole (0, 20, 100, 500 mug kg(-1)) on dopamine synthesis was determined in the dorso lateral core, ventromedial shell, and rostral pole of the nucleus accumbens . DOPA accumulation was also measured in the frontal cortex, olfactory tube rcle, and caudate nucleus of the same rats for comparative purposes. The re sults show that the three sectors of the nucleus accumbens had similar basa l levels of DOPA. Both apomorphine and quinpirole produced a decrease in th e dopamine synthesis rate in all brain regions examined. In general, the do pamine D-2/D-3 receptor agonist quinpirole produced a significantly greater decrease in DOPA accumulation than the dopamine D-1/D-2 receptor agonist a pomorphine. Within the nucleus accumbens, we found no core-shell difference s in the agonist-induced suppression of dopamine synthesis, but the rostral pole was less sensitive to the highest dose of both dopamine agonists. The se results suggest that differences in dopamine function between the core a nd shell might not involve region-specific differences in the receptor-medi ated autoregulation of dopamine neurotransmission. Moreover, the blunted ef fect of dopamine agonists in the rostral pole illustrates that this region of the accumbens is functionally distinct, possibly due to a lower dopamine receptor reserve when compared to the core and shell. (C) 2001 Elsevier Sc ience B.V. All rights reserved.