AbstractCholinergic denervation of the hippocampus by medial septal (MS) lesions results in the ingrowth of peripheral sympathetic fibers, originating from the superior cervical ganglia, into the hippocampus. To determine the effect of hippocampal sympathetic ingrowth (HSI) [3H]‐QNB (L‐quinuclidinyl [benzilic‐4, 4(n)] benzilate) binding was assessed in the dorsal and ventral hippocampus four weeks after MS lesions. In dorsal hippocampus, HSI was found to signignificantly increase the number (Bmax) of [3H]‐QNB binding sites and to normalize the decrease in affinity found in animals with MS lesions plus ganglionectomy (i. e., no ingrowth). In ventral hippocampus, HSI was found to normalize the increased number of binding sites and decreased affinity found in animals with MS lesions without ingrowth. No effect on either Kd or Bmax was found in animals that had undergone ganglionectomy with sham MS lesions. These results suggest that HSI can induce changes in hippocampal muscarinic cholinergic receptors. © 1994 Wiley‐Liss, Inc.