Early septal lesion: effect on the development of the cholinergic system in rat hippocampus.

The development of the cholinergic system in the rat hippocampal formation was studied following lesion of the septal region at an age 2--4 days postnatal (i.e. the lesion was performed prior to the establishment of the septohippocampal connections). The steep increase in acetylcholinesterase (AChE) level, that under normal conditions takes place during the second and the third week postnatal, was not observed in early lesioned animals, and AChE level at maturity was about 30% of control. AChE level of adult-lesioned animals was about 15% of control, suggesting an age-dependent plasticity in response to the lesion. Early deafferentation did not seem to alter the pattern of development of muscarinic binding sites as measured by specific binding of [3H]quinuclidinyl benzilate ([3H]QNB). Total [3H]QNB bound per hippocampus of adult, early-lesioned animals was about 70% of control, but this reduction could be accounted for by the atrophy observed in the hippocampal formation following early lesion. Binding of [3H]QNB per protein in early lesioned animals did not differ from normal. Thus the development and the level of muscarinic binding sites in the hippocampal formation do not seem to depend upon normal establishment of presynaptic contacts.