NADPH-D POSITIVE NEURONS IN THE DEVELOPING SOMATOSENSORY CORTEX OF THE RAT - EFFECTS OF EARLY AND LATE ENVIRONMENTAL ENRICHMENT

The effects of environmental enrichment upon the topographic arrangeme nt of NADPH diaphorase-positive neurons (NADPH-d(+) neurons) was studi ed in the somatosensory cortex of 56 Sprague-Dawley albino rats during early stages of development (18th, 24th, 30th and 60th postnatal days ). This diaphorase is easily demonstrable, providing a convenient mark er for quantitative studies. Environmental enrichment diminished the n umber of NADPH-d(+) neurons and exerted its maximal influence during l actation, a time of exceptional cortical susceptibility. This implies that the magnitude of such effects on the density of NADPH-d(+) neuron s is age-dependent. Furthermore, it was found that the experience-depe ndent cortical changes persisted after a subsequent period without env ironmental stimulation. The effects of early environmental enrichment did not occur uniformly throughout the cerebral hemispheres but, inste ad, such effects were maximal in the latero-ventral sector of the cere bral cortex where a dramatic reduction in the number of NADPH-d(+) neu rons was observed. Particularly striking was the existence of a latero -medial sequence of NADPH-d(+) neurons in the infragranular layer and a reversed distribution of labeled cells, in the supragranular layer. Both ontogenetic sequences of NADPH-d(+) neurons remained unchanged du ring postnatal development in controls and enriched subjects (18th-60t h postnatal days). (C) 1998 Elsevier Science B.V.