Selective loss of cholinergic receptors following unilateral intracortical injection of volkensin

Abstract Experimental lesions and quantitative autoradiography were used to investigate the cellular distribution of neurotransmitter receptors in rats. Lesions were produced by intracortical injections of either volkensin or ricin. However, only the former is retrogradely transported and volkensin treatment causes significant loss of contralateral cortical pyramidal neurones. Binding of [ 3 H]pirenzepine (muscarinic M 1 receptors) and [ 3 H]nicotine was reduced in contralateral cortex in volkensin compared with ricin and/or control (uninjected) animals. However, binding of [ 3 H]8-hydroxy-2-( n -dipropylamino)tetralin (5-HT 1A receptors), [ 3 H]ketanserin (5-HT 2A receptors), and [ 3 H]1,3-dipropylcyclopentylxanthine (adenosine A 1 receptors) was unchanged. The most likely explanation for these results is that M 1 and nicotinic receptors are present in large numbers on those pyramidal neurones that are lost. The results are discussed in terms of the biology of cortical pyramidal neurones, drugs for Alzheimer's disease, and novel ligands for improving human brain scanning techniques.