Pyramidal neurones in pathological human motor cortex express nitric oxide synthase

Increased densities of nitric oxide synthase expressing neurons in the temporal cortex and the hypothalamic paraventricular nucleus of polytoxicomanic heroin overdose victims: possible implications for heroin neurotoxicity

Heroin is one of the most dangerous drugs of abuse, which may exert various neurotoxic actions on the brain (such as gray matter loss, neuronal apoptosis, mitochondrial dysfunction, synaptic defects, depression of adult neurogenensis, as well as development of spongiform leucoencephalopathy). Some of these toxic effects are probably mediated by the gas nitric oxide (NO). We studied by morphometric analysis the numerical density of neurons expressing neuronal nitric oxide synthase (nNOS) in cortical and hypothalamic areas of eight heroin overdose victims and nine matched controls. Heroin addicts showed significantly increased numerical densities of nNOS immunoreactive cells in the right temporal cortex and the left paraventricular nucleus. Remarkably, in heroin abusers, but not in controls, we observed not only immunostained interneurons, but also cortical pyramidal cells. Given that increased cellular expression of nNOS was accompanied by elevated NO generation in brains of heroin addicts, these elevated levels of NO might have contributed to some of the known toxic effects of heroin (for example, reduced adult neurogenesis, mitochondrial pathology or disturbances in synaptic functioning).

Distribution and morphology of nitrergic neurons across functional domains of the rat primary somatosensory cortex

The rat primary somatosensory cortex (S1) is remarkable for its conspicuous vertical compartmentalization in barrels and septal columns, which are additionally stratified in horizontal layers. Whereas excitatory neurons from each of these compartments perform different types of processing, the role of interneurons is much less clear. Among the numerous types of GABAergic interneurons, those producing nitric oxide (NO) are especially puzzling, since this gaseous messenger can modulate neural activity, synaptic plasticity, and neurovascular coupling. We used a quantitative morphological approach to investigate whether nitrergic interneurons, which might therefore be considered both as NO volume diffusers and as elements of local circuitry, display features that could relate to barrel cortex architecture. In fixed brain sections, nitrergic interneurons can be revealed by histochemical processing for NADPH-diaphorase (NADPHd). Here, the dendritic arbors of nitrergic neurons from different compartments of area S1 were 3D reconstructed from serial 200 μm thick sections, using 100x objective and the Neurolucida system. Standard morphological parameters were extracted for all individual arbors and compared across columns and layers. Wedge analysis was used to compute dendritic orientation indices. Supragranular (SG) layers displayed the highest density of nitrergic neurons, whereas layer IV contained nitrergic neurons with largest soma area. The highest nitrergic neuronal density was found in septa, where dendrites were previously characterized as more extense and ramified than in barrels. Dendritic arbors were not confined to the boundaries of the column nor layer of their respective soma, being mostly double-tufted and vertically oriented, except in SG layers. These data strongly suggest that nitrergic interneurons adapt their morphology to the dynamics of processing performed by cortical compartments.

Pain modulation by nitric oxide in the spinal cord

Nitric oxide (NO) is a versatile messenger molecule first associated with endothelial relaxing effects. In the central nervous system (CNS), NO synthesis is primarily triggered by activation of N-methyl-D-aspartate (NMDA) receptors and has a Janus face, with both beneficial and harmful properties. There are three isoforms of the NO synthesizing enzyme nitric oxide synthase (NOS): neuronal (nNOS), endothelial (eNOS), and inducible nitric oxide synthase (iNOS), each one involved with specific events in the brain. In the CNS, nNOS is involved with modulation of synaptic transmission through long-term potentiation in several regions, including nociceptive circuits in the spinal cord. Here, we review the role played by NO on central pain sensitization.

Histochemical characterization, distribution and morphometric analysis of NADPH diaphorase neurons in the spinal cord of the agouti

We evaluated the neuropil distribution of the enzymes NADPH diaphorase (NADPH-d) and cytochrome oxidase (CO) in the spinal cord of the agouti, a medium-sized diurnal rodent, together with the distribution pattern and morphometrical characteristics of NADPH-d reactive neurons across different spinal segments. Neuropil labeling pattern was remarkably similar for both enzymes in coronal sections: reactivity was higher in regions involved with pain processing. We found two distinct types of NADPH-d reactive neurons in the agouti's spinal cord: type I neurons had large, heavily stained cell bodies while type II neurons displayed relatively small and poorly stained somata. We concentrated our analysis on type I neurons. These were found mainly in the dorsal horn and around the central canal of every spinal segment, with a few scattered neurons located in the ventral horn of both cervical and lumbar regions. Overall, type I neurons were more numerous in the cervical region. Type I neurons were also found in the white matter, particularly in the ventral funiculum. Morphometrical analysis revealed that type I neurons located in the cervical region have dendritic trees that are more complex than those located in both lumbar and thoracic regions. In addition, NADPH-d cells located in the ventral horn had a larger cell body, especially in lumbar segments. The resulting pattern of cell body and neuropil distribution is in accordance with proposed schemes of segregation of function in the mammalian spinal cord.

Distribution of NADPH-diaphorase-positive neurons in the prefrontal cortex of the Cebus monkey

We studied the distribution of NADPH-diaphorase (NADPH-d) activity in the prefrontal cortex of normal adult Cebus apella monkeys using NADPH-d histochemical protocols. The following regions were studied: granular areas 46 and 12, dysgranular areas 9 and 13, and agranular areas 32 and Oap. NADPH-d-positive neurons were divided into two distinct types, both non-pyramidal. Type I neurons had a large soma diameter (17.24 +/- 1.73 microm) and were densely stained. More than 90% of these neurons were located in the subcortical white matter and infragranular layers. The remaining type I neurons were distributed in the supragranular layers. Type II neurons had a small, round or oval soma (9.83 +/- 1.03 microm), and their staining pattern varied markedly. Type II neurons were distributed throughout the cortex, with their greatest numerical density being observed in layers II and III. In granular areas, the number of type II neurons was up to 20 times that of type I neurons, but this proportion was smaller in agranular areas. Areal density of type II neurons was maximum in the supragranular layers of granular areas and minimum in agranular areas. Statistical analysis revealed that these areal differences were significant when comparing some specific areas. In conclusion, our results indicate a predominance of NADPH-d-positive cells in supragranular layers of granular areas in the Cebus prefrontal cortex. These findings support previous observations on the role of type II neurons as a new cortical nitric oxide source in supragranular cortical layers in primates, and their potential contribution to cortical neuronal activation in advanced mammals.

Differential distribution of NADPH-diaphorase histochemistry in human cerebral cortex

Beta-nicotinamidedinucleotide phosphate diaphorase (NADPH-d) colocalizes with NOS in the central nervous system. Two types of NADPH-d-positive neurons are present in the primate cerebral cortex: type 1, intensely and Golgi-like labeled neurons, a subset of GABAergic interneurons; type 2, lightly labeled neurons (divided into two subclasses, a first one having a lightly stained cell body bearing only one short process, and a second one showing intense NADPH-d staining with short processes extending radially). We have analyzed the distribution of NADPH-d activity in human frontal, temporal, and occipital cortical areas, finding remarkable laminar and interareal differences in cell size and distribution of the different cell types. There was a clear bias for type 1 neurons in infragranular layers in all areas considered; both in supra- and infragranular layers, their density was highest in frontal, and lowest in temporal cortex. The density of type 2 neurons was lower supragranularly in temporal cortex and infragranularly in occipital cortex. The overall density of type 2 cells was remarkably higher in occipital cortex than in the temporal and frontal ones. Type 1 neurons were significantly larger than type 2, and were smaller in the supragranular than in the infragranular subzone in occipital and temporal cortex. Type 1 cells were significantly larger in frontal cortex than in occipital and temporal cortex, and type 2 cells were significantly smaller in occipital than in temporal and frontal cortex. These area-related differences might reflect differences between heterotypic and homotypic cortex in the regulation of cortical blood flow.

A morphometric study of the progressive changes on NADPH diaphorase activity in the developing rat's barrel field

The distribution of NADPH diaphorase (NADPH-d)/nitric oxide synthase (NOS) neurons was evaluated during the postnatal development of the primary somatosensory cortex (SI) of the rat. Both cell counts and area measurements of barrel fields were carried out throughout cortical maturation. In addition, NADPH-d and cytochrome oxidase (CO) activities were also compared in both coronal and tangential sections of rat SI between postnatal days (P) 10 and 90. Throughout this period, the neuropil distributions of both enzymes presented a remarkable similarity and have not changed noticeably. Their distribution pattern show the PMBSF as a two-compartmented structure, displaying a highly reactive region (barrel hollows) flanked by less reactive regions (barrel septa). The number of NADPH-d neurons increased significantly in the barrel fields between P10 and P23, with peak at P23. The dendritic arborization of NADPH-d neurons became more elaborated during barrel development. In all ages evaluated, the number of NADPH-d cells was always higher in septa than in the barrel hollows. Both high neuropil reactivity and differential distribution of NADPH-d neurons during SI development suggest a role for nitric oxide throughout barrel field maturation.

Cytochemical correlates of the sleep-wake interface: concerted expression of brain-derived nitric oxide synthase (bNOS) and the nicotinic acetylcholine receptor (nAChR) in a columnoid organization of the primate prefrontal cortex

Nitric oxide (NO) was recently proposed to be involved in the sleep-wake cycle and cortical spreading depression. As a structural correlate of these functions, we found that bNOS IR was expressed by three cell types in the prefrontal cortex, viz. bipolar, multipolar, and stellate cells. Dendrites of bipolar cells established bundles resulting in a columnoid organization; in addition, the monoclonal antibody mAb 35 which labels subunits alpha1, alpha3 and alpha5 of nAChR, also visualized apical axons proceeding alongside the columnoids. In contrast, alpha-bungarotoxin which labels the alpha7-subunit of nAChR, visualized only perikarya of interneurons from where the apical axons arose. In the prefrontal cortex of monkeys which were anesthetized for 6-24 hours, only traces of the columnoid organization were found, while perikaryal bNOS and nAChR were invariably expressed. It is suggested that interactions between NO and presynaptically released ACh might be involved in cortical functions such as the sleep/wake cycle.

Aberrant expression of NOS isoforms in Alzheimer's disease is structurally related to nitrotyrosine formation

Various isoforms of the nitric oxide (NO) producing enzyme nitric oxide synthase (NOS) are elevated in Alzheimer's disease (AD) indicating a critical role for NO in the pathomechanism. NO can react with superoxide to generate peroxynitrite, a process referred to as oxidative stress, which is likely to play a role in AD. Peroxynitrite in turn, nitrates tyrosine residues to form nitrotyrosine which can be identified immunohistochemically. To study the potential structural link between the increased synthesis of NO and the deposition of nitrotyrosine in AD, we analyzed the expression of neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS) in AD and control brain, and compared the localization with the distribution of nitrotyrosine. Nitrotyrosine was detected in neurons, astrocytes and blood vessels in AD cases. Aberrant expression of nNOS in cortical pyramidal cells was highly co-localized with nitrotyrosine. Furthermore, iNOS and eNOS were highly expressed in astrocytes in AD. In addition, double immunolabeling studies revealed that in these glial cells iNOS and eNOS are co-localized with nitrotyrosine. Therefore, it is suggested that increased expression of all NOS isoforms in astrocytes and neurons contributes to the synthesis of peroxynitrite which leads to generation of nitrotyrosine. In view of the wide range of isoform-specific NOS inhibitors, the determination of the most responsible isoform of NOS for the formation of peroxynitrite in AD could be of therapeutic importance in the treatment of Alzheimer's disease.

Aberrant expression of nNOS in pyramidal neurons in Alzheimer's disease is highly co-localized with p21ras and p16INK4a

Aberrancies of growth and proliferation-regulating mechanisms might be critically involved in the processes of neurodegeneration in Alzheimer's disease (AD). Expression of p21ras and further downstream signalling elements involved in regulation of proliferation and differentiation as, for example, MEK, ERK1/2, cyclins, cyclin-dependent kinases and their inhibitors such as those of the p16INK4a family, are elevated early during the course of neurodegeneration. Activation of p21ras can also directly be triggered by nitric oxide (NO), synthesized in the brain by various isoforms of nitric oxide synthase (NOS) that might be differentially involved into the pathomechanism of AD. To study the potential link of NO and critical regulators of cellular proliferation and differentiation in the process of neurofibrillary degeneration, we analyzed the expression pattern of NOS-isoforms, p21ras and p16INK4a compared to neurofibrillary degeneration in AD. Additionally to its expression in a subtype of cortical interneurons that contain the nNOS-isoform also in normal brain, nNOS was detected in pyramidal neurons containing neurofibrillary tangles or were even unaffected by neurofibrillary degeneration. Expression of nNOS in these neurons was highly co-localized with p21ras and p16INK4a. Because endogenous NO can activate p21ras in the same cell which in turn leads to cellular activation and stimulation of NOS expression [H.M. Lander, J.S. Ogiste, S.F.A. Pearce, R. Levi, A. Novogrodsky, Nitric oxide-stimulated guanine nucleotide exchange on p21 ras, J. Biol. Chem. 270 (1995) 7017-7020], the high level of co-expression of NOS and p21ras in neurons vulnerable to neurofibrillary degeneration early in the course of AD thus provides the basis for an autocrine feedback mechanism that might exacerbate the progression of neurodegeneration in a self-propagating manner.

Nitric oxide and glutamate interaction in the control of cortical and hippocampal excitability

PURPOSE

We investigated the role of nitric oxide (NO) as a new neurotransmitter in the control of excitability of the hippocampus and the cerebral cortex, as well as the possible functional interaction between NO and the glutamate systems.

METHODS

The experiments were performed on anesthetized rats. The bioelectrical activities of the somatosensory cortex and the CA1 region of the hippocampus of these rats were recorded. Pharmacologic inhibition of NO synthase (NOS) through the nonselective and brain-selective inhibitors, N-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), was performed.

RESULTS

The treatments caused the appearance of an interictal discharge activity in both the structures. The latency of induction and the duration of the interictal discharge activity were strictly related to the dose of NOS inhibitor used. In some cases, after L-NAME treatment at high doses, it was possible to note spike and wave afterdischarge activity in the hippocampus. All the NOS inhibitor-mediated excitatory effects were abolished by intraperitoneal (i.p.) pretreatment with the N-methyl-D-aspartic acid (NMDA) receptor antagonists (DL-2-amino-5-phosphonovaleric acid, 2-APV; dizolcipine, MK-801) and partly suppressed after the i.p. injection of the non-NMDA antagonist (6-cyano-7-nitroquinoxaline-2,3-dione; CNQX).

CONCLUSIONS

All data showed that the reduction of NO levels in the nervous system causes the functional prevalence of the excitatory neurotransmission, which is probably due to an NMDA overactivity caused by the absence of the NO-mediated modulatory action. Thus, it is possible to hypothesize a neuroprotective role for NO, probably through a selective desensitization of the NMDA receptors.

Nitrinergic neurons in the developing and adult human telencephalon: transient and permanent patterns of expression in comparison to other mammals

A subpopulation of cerebral cortical neurons constitutively express nitric oxide synthase (NOS) and, upon demand, produce a novel messenger molecule nitric oxide (NO) with a variety of proposed roles in the developing, adult, and diseased brain. With respect to the intensity of their histochemical (NADPH-diaphorase histochemistry) and immunocytochemical (nNOS and eNOS immunocytochemistry) staining, these nitrinergic neurons are generally divided in type I and type II cells. Type I cells are usually large, intensely stained interneurons, scattered throughout all cortical layers; they frequently co-express GABA, neuropeptide Y, and somatostatin, but rarely contain calcium-binding proteins. Type II cells are small and lightly to moderately stained, about 20-fold more numerous than type I cells, located exclusively in supragranular layers, and found almost exclusively in the primate and human brain. In the developing cerebral cortex, nitrinergic neurons are among the earliest differentiating neurons, mostly because the dominant population of prenatal nitrinergic neurons are specific fetal subplate and Cajal-Retzius cells, which are the earliest generated neurons of the cortical anlage. However, at least in the human brain, a subpopulation of principal (pyramidal) cortical neurons transiently express NOS proteins in a regionally specific manner. In fact, transient overexpression of NOS-activity is a well-documented phenomenon in the developing mammalian cerebral cortex, suggesting that nitric oxide plays a significant role in the establishment and refinement of the cortical synaptic circuitry. Nitrinergic neurons are also present in human fetal basal forebrain and basal ganglia from 15 weeks of gestation onwards, thus being among the first chemically differentiated neurons within these brain regions. Finally, a subpopulation of human dorsal pallidal neurons transiently express NADPH-diaphorase activity during midgestation.

Developmental characteristics of neuronal nitric oxide synthase (nNOS) immunoreactive neurons in fetal to adolescent human brains

The developmental characteristics of the neuronal nitric oxide synthase (nNOS) immunoreactive neurons in the human brain were studied. In the frontal lobe, nNOS immunoreactive cells appeared as early as 18 gestational weeks (GW) in the subcortical plate and then increased predominantly in the subcortical white matter during the fetal period, while weakly immunoreactive neurons were found in the cortical II-IV layers after 26 GW. In the basal ganglia, immunoreactive neurons could be detected in the striatum as early as 13 GW, and then showed a transient increase with peaks at 23-24 GW and 33-36 GW in the putamen and caudate nucleus, respectively. In the cerebellum, immunoreactivity was detected in the Purkinje and basket cells after 23 GW and 31 GW, respectively. The immunoreactivity of internal granule cells was constantly weak. In the brain stem, constant and intense immunoreactive neurons were found in the central gray, pedunculopontine tegmental nucleus, solitary tract nucleus, and lateral reticular nucleus. The immunoreactivity in the neurons of the pontine nucleus and inferior olivary nucleus was transiently increased, with peaks at 38-40 GW and 23-24 GW, respectively. This characteristic nNOS development suggests that transient nNOS hyperproduction may contribute to neuron maturation as well as vulnerability in each period and region, and NO may play an important role in the basic development of human brain functions.

MPP+ induced substantia nigra degeneration is attenuated in nNOS knockout mice

Recent studies showed that neuronal nitric oxide synthase (nNOS) plays a role in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity. In the present study we examined the effects of striatal injection of 1-methyl-4-phenylpyridinium (MPP+) on substantia nigra degeneration in mutant mice lacking the nNOS gene or the endothelial nitric oxide synthase (eNOS) gene. Both striatal lesion volume and substantia nigra degeneration were significantly attenuated in the nNOS mutant mice but not in the eNOS mutant mice. The mice lacking nNOS showed a significant attenuation of MPP+(-) induced increases of 3-nitrotyrosine concentrations in the striatum. In a separate experiment administration of 7-nitroindazole for 48 h after MPP+ injections significantly attenuated substantia nigra degeneration in rats. Immunohistochemical studies showed apposition of nNOS-positive neuronal processes on tyrosine hydroxylase-positive neurons. These results provide further evidence that neuronally derived NO and peroxynitrite play a role in MPP+ neurotoxicity.