Adenosine A1 receptors mediate the inhibitory effects of exogenous adenosine in the rat olfactory cortex slice

A study has been undertaken to identify the category of receptors mediating the inhibitory effects of adenosine on evoked activity in slices of olfactory cortex in the rat. The approach has been to measure the relative potencies of adenosine and a range of structural analogues [2-chloroadenosine, 2' deoxyadenosine, cyclohexyladenosine, (-)-5'N-ethyl-carboxamide adenosine and N6(L-2-phenylisopropyl)adenosine] required to: inhibit excitatory transmission at the lateral olfactory tract-pyramidal cell synapse; inhibit the specific binding of [3H]cyclohexyladenosine to membrane preparations and evoke formation of cyclic AMP. In contrast to the relative concentrations of the analogues necessary to increase levels of cyclic AMP, those required to inhibit synaptic transmission were characteristic of a selectivity for adenosine A1 receptors. The presence of adenosine A1 receptors has been demonstrated directly by characterizing the binding of [3H]cyclohexyladenosine to membranes prepared from slices of olfactory cortex. It is concluded that inhibition of transmission at the lateral olfactory tract-pyramical cell synapse by adenosine is mediated by receptors of the A1 category.