INFLUENCE OF PLACE LEARNING ON SOMATOSTATIN LEVELS IN THE RAT-BRAIN FOLLOWING ENVIRONMENTAL DEPRIVATION

We have previously reported increased somatostatin levels in the cereb ral cortex of rats housed in impoverished environment and subsequently subjected to a behavioural testing procedure, consisting of open-fiel d exposure and spatial learning. The aim of the present study was to e valuate the degree of neurochemical specificity of the activation of s omatostatin neurotransmission and to examine whether the altered level s were due to learning stimulation. Adult rats, previously housed indi vidually for 30 days, were exposed to repeated sessions of a spatial l earning task (2 days or 14 days) or repeated sessions of free swimming (14 days). The training sessions of the 14 day group consisted in rec urrently changed position of the platform in a learning-set paradigm. Our data showed increased somatostatin immunoreactivity, and unchanged substance P immunoreactivity in the posterior part of the cerebral co rtex. However, somatostatin levels increased to a similar extent follo wing 14 days of repeated spatial learning sessions as free swimming se ssions. We conclude that the activity of the cortical somatostatin sys tem appears to be sensitive to environmentally induced sensorimotor st imulation in general, rather than learning per se. Thus, external stim ulation of early clinical dementia patients with preserved sensorimoto r receptivity, in an attempt to restore cognitive function, might be a ssociated with altered somatostatin levels.