The effect of medial septum cholinergic lesion on suppression of hippocampal C-FOS in the rat formalin model of pain

Abstract

This study investigated whether the destruction of the cholinergic neurons in medial septum-vertical limb of diagonal band of Broca (MS-VLDBB) region influenced the suppression of hippocampal CA1 c-Fos in the formalin model of inflammatory pain. c-Fos is a transcription protein that is expressed in neurons on synaptic excitation. Further, the study also examined whether the cholinergic lesion modulated animal nociceptive behavior, spinal c-Fos expression and morphine antinociception in the formalin test. The results indicate that near complete destruction of cholinergic neurons in MS-VLDBB with intraseptal administration of the immunotoxin 192 IgG-saporin prevented formalin-induced suppression of c-Fos in dorsal CA1 and CA3 without affecting the corresponding animal behavior and expression of spinal c-Fos. This suggests that the destruction of MS-VLDBB cholinergic neurons influenced the suppression of c-Fos in dorsal CA1 and CA3 via modulation of the hippocampal network that was not secondary to changes in nociceptive behavior and rostral transfer of nociceptive signal from the spinal cord. However, MS-VLDBB cholinergic lesion did not have a consistently effect on morphine-antinociception in the formalin test.