Influence of tooth-loss and concomitant masticatory alterations on cholinergic neurons in rats: immunohistochemical and biochemical studies.

The influence of tooth loss on the viability of cholinergic neurons was examined in rats. At 25th postnatal week, rats were divided into the three groups; a control group fed a solid diet, a soft diet group fed a powder diet and a molar crown-less group in which all molar crowns were removed and the powder diet was given. At 15 and 35 weeks post-treatment, the number of choline acetyltransferase (ChAT)-positive neurons in the nucleus of the diagonal band/medial septal nucleus (NDB/MS) was significantly smaller in the molar crown-less group than in the control group (P < 0.01). This was not the case in the pedunculopontine tegmental nucleus or (PPT) or in the trigeminal motor nucleus. Biochemical assay showed no statistically significant differences in choline concentrations in the hippocampus between the control and the molar crown-less group both at 15 and at 35 weeks post-treatment. Nevertheless, acetylcholine (ACh) concentration in the hippocampus of the molar crown-less group was significantly lower than that of the control group at 15 weeks post-treatment (P < 0.05). Taken together, a decrease of oral sensory information may have caused a reduction in the number of ChAT-positive neurons selectively in NDB/MS, which in turn caused a decline of ACh concentrations in the hippocampus.