Alpha 1B-adrenoceptor-mediated excitation of piriform cortical interneurons

Pharmacological techniques have defined the existence of two different alpha 1-adrenoceptors, the alpha 1A- and alpha 1B-adrenoceptor subtypes and both of these receptors have been cloned in addition to a cloned alpha 1d-adrenoceptor. A subpopulation of interneurons in layer III of the rat piriform cortex that are excited by 5-hydroxytryptamine (5-HT) via 5-HT2A receptors are also excited by norepinephrine via alpha 1-adrenoceptors. In the present study we determined the pA2 values against the norepinephrine-mediated excitation of piriform cortical interneurons for a number of antagonists that are (1) not selective for alpha 1A- or alpha 1B-adrenoceptors (prazosin), (2) selective for alpha 1A-adrenoceptors (5-methyl urapidil, 2-(2,6-dimethoxy-phenoxyethyl)- aminomethyl-1,4-benzodioxane hydrochloride (WB 4101), benoxathian, phentolamine) and (3) selective for alpha 1B-adrenoceptors (spiperone and risperidone). The pA2 values for the antagonist blockade of norepinephrine-mediated interneuron excitation were significantly correlated to literature values for the pKi values of antagonist binding to the alpha 1B-adrenoceptor (r = 0.919) and the cloned alpha 1b-adrenoceptor (r = 0.849) but were not correlated to the pKi values of antagonist binding to the alpha 1A-adrenoceptor or the cloned alpha 1a- and alpha 1d-adrenoceptor. Thus, we conclude that this population of piriform cortical interneurons is excited by norepinephrine via alpha 1B-adrenoceptors.