Using NADPH-diaphorase histochemistry, distribution of reactive neurons in the forebrain structures and motor cortex of rats was studied. Some reactive (NO-generating) neurons are associated with microvessels and, thus, can be involved in the regulation of regional blood flow. Almost ten years ago, it was found that an endothelium-derived relaxing factor (EDRF) is equivalent to nitric oxide (NO). For this finding, three American scientists, Robert F. Furchgott, Louis J. Ignarro, and Ferid Murad, were awarded the Noble Prize for Medicine in 1998. In the basal forebrain, there are four groups of cholinergic NO-generating neurons (Ch1-Ch4) projecting to the cortex. Thus, ascending pathways from the forebrain can also be involved in cortical activation through the release of NO [1,2]. Such corticopetal NO synthase (NOS)-containing cells and cholinergic networks in the cortex are implicated in several important brain phenomena, including arousal, attention, cortical plasticity, and memory. Abnormalities of the L-arginine-NO synthesis pathways in various structures of the basal forebrain and cortex are associated with severe impairment of cerebral functions. Dementia related to Alzheimer's disease results to a significant extent from a loss of the NADPH-diaphorase/NOS activity in the cortex [3][4][5]. It should be emphasized that colocalization of NOS immunoreactivity and NADPH reactivity has been demonstrated in a number of brain neurons. Cholinergic innervation of the cortex has been extensively studied. In humans, its main center of origin was identified as the nucleus basalis of Meynert; its equivalent in the rat is the substantia innominata (SI). Electron microscopic studies demonstrated that basal forebrain neurons project preferentially to the cortical pyramidal and NOScontaining non-pyramidal neurons; however, there are also projections to intraparenchymal arterioles, microvessels, and even capillaries. A significant proportion of these projections are cholinergic or GABA-ergic; in addition, they are NADPH diaphorasereactive [6,7].Based on the data on the co-localization of GABA and NADPH diaphorase (NADPH-d) in a population of cortical non-pyramidal neurons, or on that of acetylcholine and NADPH-d in a subpopulation of basal forebrain neurons, we suggested that these cells and their fibers and dendrites can be implicated in structural associations with the arterioles and microvessels.All experiments were carried out in accordance with the European Communities Council Directive of November 24, 1986 (86/609/EEC). Male Wistar rats (n = 8) weighing 250-300 g were used in the study. Frontal frozen sections of the brain (40 µm thick) were cut. The NADPH-d reactivity was detected according to a slightly modified standard histochemical method; for intensification of the reaction, disodium salt of malic acid (1.2 mg/ml; Sigma, USA) was added to the staining solution [8].The NADPH-d reactivity and distribution density of reactive neurons in the limbic structures and primary motor cortex were estimated. The neurons were ...

We estimated expression of the c-fos gene (a marker of increase in neuronal activity) and manifestations of the histochemical reaction to NADPH-diaphorase (a marker of NO-generating neurons) in the medial prefrontal cortex (MPFC) and forebrain limbic structures of rats in the norm, in the state of starvation, and during realization of long-lasting (60 min) periodic (several times per minute) food-procuring movements of the forelimb. The starvation state or realization of motivated stereotyped forelimb movements were related to significant bilateral increases (Р < 0.05) in the levels of c-fos expression in the anterior olfactory (AOP) and cortical (ACo) nuclei and the central (Ce) and basolateral (BLA) nuclei of the amygdala, and also in the pyriform (Pyr), prelimbic (PrL), and inferior limbic (IL) cortices. The described findings demonstrate that the high Fos immunoreactivity in the MPFС and amygdalar structures is related to the motivation state in С and amygdalar structures is related to the motivation state in С animals and reflects the active involvement of limbic cerebral structures in the formation of motor programs and also in the stabilization and realization of operant reflexes.

No abstract

We estimated in rats the expression of early gene c-fos (marker of neuronal activation) and NADPH-diaphorase activity (NO-synthase marker) in the limbic structures of the basal forebrain and in the hypothalamus. Estimations were performed in the norm, in the state of starvation, and after realization of long-lasting (repeated 4 to 12 times per minute for 30 min) motivated stereotyped food-procuring forelimb movements. In food-deprived animals, a significantly greater (Р < 0.05), as compared with the control, number of Fosimmunoreactive (Fos-ir) and NADPH-diaphorase-reactive (NADPH-dr) neurons was observed in limbic structures, namely in the medial septum (MS), nuclei of the vertical and horizontal branches of the diagonal fascia (VDB and НDB), magnocellular preoptic nucleus (MCPO), complex of the substantia innominata−basal nucleus of Meynert of the pallidum, SI-GP(B), as well as in the laterodorsal tegmental nucleus (LDTg), medial part of the pallidum (MGP), paraventricular and lateral nuclei of the hypothalamus (Pa and LH), and islands of Calleja (ICj and ICjM). In the limbic structures and pontine nuclei of rats of the experimental group (that performed operant movements), greater mean densities of labeled neurons were found in the succession LDTg < SI < MCPO < GP(B) < MS < VDB < HDB. The maximum mean density of Fos-ir neurons (13.8 ± 0.9 labeled nuclei within 200 × 200 µm 2 area) was found in the HDB. In the hypothalamic nuclei of starving rats, c-fos expression was two times higher than that in the control. After realization of operant movements, the intensity of expression in the LH was somewhat smaller, while in the Ра it was higher. The maximum density of NADPH-dr neurons was observed in the Pa (303.4 ± 18.7 cells), in the ICj and ICjM (287 ± 11.6 and 260 ± ± 8.7 neurons, respectively), and in the MGP (93 ± 6.7 labeled cells). When analyzing the distribution of labeled neurons in experimental rats, we found high densities of double-labeled cells (Fos + NADPH-d positivity) in the Pa, MGP, ICj, and ICjM. Such specificity of changes in the c-fos expression and NADPH-d reactivity in the hypothalamus correlates, perhaps, with the formation of motivation signals related to a delay in food accessibility and supply of food. Modifications of neuronal activity in limbic structures reflect involvement of the latter in the formation of motor programs for food-procuring movements and their realization.

No abstract