The effect of hippocampal sympathetic ingrowth and cholinergic denervation on hippocampal M2 cholinergic receptors.

After cholinergic denervation of the hippocampus, via medial septal (MS) lesions, peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the hippocampus. In this study, we sought to determine the effect of hippocampal sympathetic ingrowth (HSI) on the M2 subtype of muscarinic cholinergic receptors, by examining the membrane binding of [3H]AF-DX 384 in hippocampal tissue from control rats, rats with HSI and rats with MS lesions + concurrent ganglionectomy (CD group). In dorsal hippocampus, Kd was found to be increased while Bmax was decreased in the CD group as compared with both the HSI and control group which did not differ from one another. In ventral hippocampus, Kd was found to be increased while Bmax was decreased in the CD group when compared only with the control group. These results suggest that sympathetic ingrowth, which has its greatest concentration in dorsal hippocampus, can 'normalize' the M2 receptor in hippocampus.