Activation of D1 and D2 dopamine receptors increases the activity of the somatostatin receptor-effector system in the rat frontoparietal cortex

The role of dopamine D1 and D2 receptor subtypes in the regulation, in vivo , of the somatostatin (SRIF) receptor-effector system in rat frontoparietal cortex was investigated. The D1-receptor agonist SKF 38393 (4 mg/kg) or th e D2-receptor agonist bromocriptine (2 mg/kg), administered intraperitoneal ly to rats, increased the number of SRIF receptors without altering the aff inity constant, an effect antagonized by both SCH 23390 (0.25 mg/kg) and ra clopride (5 mg/kg), D1 and D2 receptor antagonists, respectively. These ant agonists alone had no effect on [I-125]Tyr(3) octreotide binding to its rec eptors. No change in binding was detected when the dopamine agonists were a dded in vitro. Basal adenylyl cyclase (AC) activity was increased by SKF 38 393 treatment and decreased by bromocriptine. Octreotide (SMS 201-995)-medi ated inhibition of basal and forskolin-stimulated AC was increased by SKF 3 8393 or bromocriptine treatment. In frontoparietal cortical slices, basal i nositol-1,4,5-triphosphate (IP,) levels were decreased by bromocriptine tre atment but were unaffected by SKF 38393. SMS 201-995 increased the IF, accu mulation in control, SKF 38393-, and bromocriptine-treated rats. Insofar as SRIF and dopamine appear to be involved in motor regulation and could well modulate somatosensory functions in frontal and parietal cortex, respectiv ely, heterologous receptor regulation may have important repercussions rega rding the control exerted by these neurotransmitters on frontal and parieta l cortical function in the intact animal. (C) 2000 Wiley-Liss, Inc.