Activation of identified septo-hippocampal neurons by noxious peripheral stimulation.

Septo-hippocampal neurons (SHNs) were recorded from the medial septum-diagonal band area of rats anaesthetized with either urethane or fluothane. They were identified by their antidromic response to the electrical stimulation of the fimbria. Their responses to peripheral somatic noxious and non-noxious stimulation were studied. Non-noxious natural stimulations were relatively ineffective. In contrast, 68% of the SHNs were driven by noxious stimulation. The SHNs could be driven either by mechanical or thermal stimulation. Intraperitoneal injection of bradykinin excited about half of the SHNs. Some neurons were able to encode stimulus intensity (strength of the mechanical stimulation and/or temperature of the thermal stimulation). The receptive fields of the SHNs were large, usually involving half of the body or the whole body surface. These results suggest that SHNs, which are at the origin of the cholinergic septo-hippocampal pathway, might be involved in cerebral mechanisms related to nociception.