Abstract
The role of the central cholinergic system, particulary the hippocampus, in cognitive functions including learning and memory is now well established (Kadar et al., 1990). In aged rats, morphological alterations as well as impaired hippocampal synaptic plasticity have been shown to correlate well with learning deficits (Kadar et al., 1990; Levy et al., 1994). Recently, it has been suggested that nitric oxide (NO), a neuronal messenger, may play a role in the process of learning through facilitation of long-term potentiation (Bon et al., 1992). Thus, changes in NO activity may be associated with modifications in learning and memory. In spite of the elaborative study of the interaction between NO and cognitive functions, little is known about the age-related changes in NOS activity. The aim of the present study was to explore the age-related changes in the activity and distribution of NO synthase (NOS), the synthesizing enzyme for NO in the hippocampus, and to relate them to the cognitive impairment observed in normal aging. For this purpose, young and old Sprague Dawely rats, were tested for their performance in the Morris water maze (MWM), after which their brains were processed for histochemical evaluation of NOS activity by the NADPH-diaphorase reaction. There is evidence for neuronal NADPH-diaphorase being a NOS in the brain (Bredt et al., 1991).
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