OUTWARD CURRENT PRODUCED BY SOMATOSTATIN (SRIF) IN RAT ANTERIOR CINGULATE PYRAMIDAL CELLS IN-VITRO

1 A high density of receptors for somatostatin (SRIF) exists in the an terior cingulate cortex but their function is unknown. Whole-cell patc h clamp recordings were made from visualized deep layer pyramidal cell s of the rat anterior cingulate cortex contained in isolated brain sli ces to investigate the putative effects of SRIF and to identify the re ceptor subtype(s) involved. 2 SRIF (1-1000 nM) produced a concentratio n-dependent outward current which was associated with an increased mem brane conductance, was sensitive to Ba2+ (300 mu M-1 mM), and was abse nt in the presence of a maximal concentration of the GABA(B) receptor agonist, baclofen (100 mu M). These observations suggest the outward c urrent was carried by K+ ions. 3 SRIF analogues also elicited outward currents with a rank potency order of (EC50, nM): octreotide (1.8) > B IM-23027 (3.7) > SRIF (20) = L-362,855 (20). BIM-23056 was without ago nist or antagonist activity. Responses to L-362,855 were unlike those to the other agonists since they were sustained for the duration of th e application. 4 The sst(2) receptor antagonist, L-Tyr(8)Cyanamid 1548 06 (1 mu M), had no effect alone but partially reversed responses to s ubmaximal concentrations of SRIF (100 nM, 44 +/- 6% reversal) and L-36 2,855 (100 nM, 70 +/- 6% reversal) and fully reversed the response to BIM-23027 (10 nM). In contrast, L-Tyr(8)Cyanamid 154806 did not antago nize the response to baclofen (10 mu M). 5 We conclude that SRIF activ ates a K+ conductance in anterior cingulate pyramidal neurones via an action predominantly at sst(2) receptors.