NADPH-diaphorase activity and neurovascular coupling in the rat cerebral cortex

The distribution of NADPH-diaphorase-reactive (NADPH-dr) neurons and neuronal processes in the cerebral cortex and basal forebrain and their association with parenchymal vessels were studied in normal adult rats using NADPH-d histochemical protocol. The intensely stained cortical interneurons and reactive subcortically originating afferents, and stained microvessels were examined through a light microscope at law (x250) and high (x630) magnifications. NADPH-dr interneurons were concentrated in layers 2-6 of the M1 and M2 areas. However, clear predominance in their concentration (14 +/- 0.8 P < 0.05 per section) was found in layer 6. A mean number of labeled neurons in auditory (AuV), granular and agranular (GI, AIP) areas of the insular cortex was calculated to reach 12.3 +/- 0.7, 18.5 +/- 1.0 and 23.3 +/- 1.7 units per section, respectively (P < 0.05). The distinct apposition of labelled neurons to intracortical vessels was found in the M1, M2. The order of frequency of neurovascular coupling in different zones of the cerebral cortex was as following sequence: AuV (31.2%, n = 1040) > GI (18.0%, n = 640) > S1 (13.3%, n = 720) > M1 (6.3%, n = 1360). A large number of structural associations between labeled cells and vessels in the temporal and insular cortex indicate that NADPH-d-reactive interneurons can contribute to regulation of the cerebral regional blood flow in these areas.