Cortically driven Fos induction in the striatum is amplified by local dopamine D2-class receptor blockade

Dopamine D2-class receptors have been shown to control the excitability of striatal neurons in response to cortical activation. It has been unclear, h owever, whether such receptors could regulate the number of striatal neuron s activated by cortical stimulation, and thus affect the population respons e of the striatum to its cortical inputs. We used Fos induction as a readou t to measure the ensemble response of striatal neurons to localized stimula tion of the frontal cortex and tested for the effects of D2-class dopamine receptor blockade on this response. In freely moving rats, we stimulated th e frontal cortex by local epidural application of a dose of a GABA(A) recep tor antagonist (picrotoxin) just threshold for inducing Fos in the striatum . We combined this treatment with D2-class dopamine receptor antagonist tre atments at dose levels also just threshold for inducing Fos, using either ( i) systemic haloperidol or (ii) intrastriatal (-)sulpiride. Both systemic a nd intrastriatal blockade of D2-class receptors sharply increased the numbe rs of striatal neurons exhibiting cortically evoked Fos induction. These fi ndings suggest that local activation of intrastriatal D2-class dopamine rec eptors can regulate the number of striatal neurons responsive to cortical i nputs, thus dynamically shaping the flow of information through the striatu m.