Changes in Cortical Nicotinic Acetylcholine Receptor Numbers Following Unilateral Destruction of Pyramidal Neurones by Intrastriatal Volkensin Injection

Experimental lesions using the retrogradely transported toxic lectin, volkensin, were used in conjunction with quantitative autoradiography to investigate the cellular localization of nicotinic and adenosine A₁receptors. Lesions were produced by unilateral intrastriatal injection of volkensin, ricin (another toxic lectin but not transported in the central nervous system), quinolinate, and unilateral intrathalamic injection of ibotenate. Volkensin injection significantly reduced the number and mean cell size of large, infragranular pyramidal neurones in cortical areas Fr1/Fr2 (close to the midline) and more laterally in Par1/Par2. Selective destruction of these cells was accompanied by significant increases in the binding of [³H] nicotine in cortical areas contralateral to the lesion. A small but significant reduction in the binding of [³H] 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) to adenosine A₁receptors was observed only in deep layers of Fr1/Fr2 on the side ipsilateral to the lesion. No other toxin consistently changed the binding of either ligand in control animal groups with the exception of [³H] nicotine where small reductions were observed in the middle layers of one thalamic injection group. These data indicate differential plasticity of nicotinic receptors compared with other receptors studied previously using this paradigm. In the light of these findings, nicotinic receptors are discussed as targets for pharmacological manipulation of the activity of pyramidal neurones.