Localization of nitric oxide synthase in the adult rat brain

Down-regulation of neuronal nitric oxide synthase by nitric oxide after oxygen-glucose deprivation in rat forebrain slices

The precise role that nitric oxide (NO) plays in the mechanisms of ischemic brain damage remains to be established. The expression of the inducible isoform (iNOS) of NO synthase (NOS) has been demonstrated not only in blood and glial cells using in vivo models of brain ischemia-reperfusion but also in neurons in rat forebrain slices exposed to oxygen-glucose deprivation (OGD). We have used this experimental model to study the effect of OGD on the neuronal isoform of NOS (nNOS) and iNOS. In OGD-exposed rat forebrain slices, a decrease in the calcium-dependent NOS activity was found 180 min after the OGD period, which was parallel to the increase during this period in calcium-independent NOS activity. Both dexamethasone and cycloheximide, which completely inhibited the induction of the calcium-independent NOS activity, caused a 40-70% recovery in calcium-dependent NOS activity when compared with slices collected immediately after OGD. The NO scavenger oxyhemoglobin produced complete recovery of calcium-dependent NOS activity, suggesting that NO formed after OGD is responsible for this down-regulation. Consistently, exposure to the NO donor (Z)-1-[(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-iu m-1,2-diolate (DETA-NONOate) for 180 min caused a decrease in the calcium-dependent NOS activity present in control rat forebrain slices. Furthermore, OGD and DETA-NONOate caused a decrease in level of both nNOS mRNA and protein. In summary, our results indicate that iNOS expression down-regulates nNOS activity in rat brain slices exposed to OGD. These studies suggest important and complex interactions between NOS isoforms, the elucidation of which may provide further insights into the physiological and pathophysiological events that occur during and after cerebral ischemia.

Expression of neuronal nitric oxide synthase during embryonic development of the rat cerebral cortex

The expression of neuronal nitric oxide synthase (nNOS) during the development of the rat cerebral cortex from embryonic day (E) 13 to postnatal day (P) 0 was analyzed by immunocytochemical procedures using a specific antibody against rat brain nNOS. Expression of nNOS was first seen on E14 in cells of Cajal-Retzius morphology located in the marginal zone. Neuronal NOS immunoreactivity persisted in this layer throughout the embryonic period and only began to decrease on E20, when neuronal migration is coming to an end. From E17 onwards, migrating neurons expressing nNOS were observed in the intermediate zone with their leading processes directed towards the cortical plate. At the same time, efferent nNOS-immunoreactive axons originating from cortical plate cells entered the intermediate zone. From E19 onwards, cells expressing nNOS and with the morphological characteristics of migrating cells were observed in and near the subventricular zone. Confocal analysis of double immunostaining for nNOS and glial fibrillary acidic protein or nestin showed no coexpression of nNOS and glial markers in these cells, suggesting that nNOS-positive cells leaving the subventricular zone were not glial cells. Commissural, callosal and fimbrial fibers were seen to express nNOS on E18 and E19. This expression decreased from E20 and was very weak on E21 and P0. The observations suggest that nitric oxide is synthesized during embryonic life in relation to maturational processes such as the organization of cerebral lamination, and is involved in controlling migrational processes and fiber ingrowth.

Localization of nitric oxide-synthesizing neurons sending projections to the dorsal raphe nucleus of the rat

The origin of the nerve fibers immunoreactive for neuronal nitric oxide synthase (nNOS) in the rat dorsal raphe nucleus (DRN) was determined by combining the use of cholera toxin subunit b (CTb) as a retrograde tracer and nNOS immunohistochemistry with a monoclonal anti-nNOS antibody. Double labeled CTb-nNOS cell bodies were distributed from the rostral diencephalon to the caudal medulla oblongata, in about 20 areas of the brain. Several of the areas displaying double labeled cells are known for their involvement in the control of the sleep-wake cycle and/or transmission of nociception.

Role of endogenous nitric oxide in the nucleus tratus solitarii on baroreflex control of heart rate in spontaneously hypertensive rats

OBJECTIVE

Toinvestigate the modulatory effect of endogenous nitric oxide (NO) in the nucleus tractus solitarii (NTS) on the baroreceptor reflex control of heart rate in conscious spontaneously hypertensive (SHR) and normotensive (WKY) rats.

DESIGN AND METHODS

Male age- and weight-matched SHR and WKY chronically instrumented with cannulas in the NTS, artery and vein were used. Basal pressure (AP), heart rate (HR) and reflex HR responses during loading/unloading of baroreceptors (phenylephrine/sodium nitroprusside, iv) were recorded during vehicle (3 nl/min) NG-monomethyl-L-arginine (L-NMMA) and L-arginine (L-Arg) infusions into the NTS. Constitutive NO synthase (NOS) activity was inferred by 3H-citrulline formation in the dorsal brain stem of other SHR and WKY groups.

RESULTS

In SHR a small dose of L-NMMA (30 ng/kg/min) restricted to the NTS did not change AP and HR (185+/-4 mmHg, 373+/-12 beats/min, respectively), but decreased the HR range (57+/-7 beats/min, a 34% reduction, P< 0.05) without changing further the impaired gain of baroreceptor reflex control of HR. In the WKY group similar results (significant 32% reduction in HR range, gain unchanged) were only attained with a dose 10 times higher (L-NMMA(NTS) = 300 ng/kg/min), no effect being observed with the small dose (HR range = 163+/-12 beats/min). In SHR, L-Arg(NTS) (900 ng/kg/min) did not improve baroreflex control of HR, but restored the depression of HR range when given after L-NMMA(NTS). Basal NOS activity in the dorsal brain stem was reduced in SHR (P < 0.05) when compared to WKY group.

CONCLUSIONS

NO modulates, at the NTS level, the baroreceptor reflex control of HR in both SHR and WKY not by altering the gain, but by increasing HR range during afferent stimulation. In SHR the depressed NO modulation is in accordance with the smaller NOS activity in the dorsal brain stem.

Tyrosine kinase A, galanin and nitric oxide synthase within basal forebrain neurons in the rat

Cholinergic basal forebrain neurons appear to play a key role in cognition and attention. In rat, basal forebrain neurons express multiple proteins including the high-affinity signal transducing tyrosine kinase A receptor for nerve growth factor, the neuropeptide galanin and nitric oxide synthase, a marker for the novel neurotransmitter nitric oxide. The present study was undertaken to define the relationship between neurons expressing each of these markers within the medial septum-vertical limb of the diagonal band, horizontal limb of the diagonal band and nucleus basalis in colchicine pre-treated rats. Tyrosine kinase A-immunopositive neurons were seen throughout all subfields of the basal forebrain. In contrast, nitric oxide synthase- and galanin-immunoreactive neurons were mainly distributed within the septal-diagonal band complex. Co-localization experiments revealed that virtually all nitric oxide synthase-positive neurons (visualized by nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry) also contained tyrosine kinase A, whereas many fewer tyrosine kinase A neurons were nicotinamide adenine dinucleotide phosphate-diaphorase positive within the medial septum-vertical limb of the diagonal band. Within the horizontal limb of the diagonal band, numerous nicotinamide adenine dinucleotide phosphate-diaphorase neurons expressed tyrosine kinase A, whereas only a small number of tyrosine kinase A neurons contained nicotinamide adenine dinucleotide phosphate-diaphorase. Within the nucleus basalis very few neurons were nicotinamide adenine dinucleotide phosphate-diaphorase reactive, and a minor number contained tyrosine kinase A. Additional co-localization experiments revealed minor percentages of neurons containing nicotinamide adenine dinucleotide phosphate-diaphorase and galanin immunoreactivity within the various subfields of the basal forebrain. Within the horizontal limb of the diagonal band minor numbers of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive perikarya displayed galanin. Similarly, only a few galanin-containing neurons expressed nicotinamide adenine dinucleotide phosphate-diaphorase. The existence of tyrosine kinase A, nitric oxide synthase and galanin within select neuronal subgroups of the cholinergic basal forebrain suggests that these perikarya are responsive to a complex set of chemical signals. A greater understanding of the chemical signature of the cholinergic basal forebrain neurons will provide the insight required to develop novel pharmacological approaches aimed at preventing or slowing the degenerative processes that effect these neurons in aging and pathologic disorders.

Distribution of nitric oxide synthase and nitric oxide-receptive, cyclic GMP-producing structures in the rat brain

The structures capable of synthesizing cyclic GMP in response to nitric oxide in the rat brain were compared relative to the anatomical localization of neuronal nitric oxide synthase. In order to do this, we used brain slices incubated in vitro, where cyclic GMP-synthesis was stimulated using sodium nitroprusside as a nitric oxide-donor compound, in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine. Nitric oxide-stimulated cyclic GMP synthesis was found in cells and fibers, but was especially prominent in varicose fibers throughout the rat brain. Fibers containing the nitric oxide-stimulated cyclic GMP production were present in virtually every area of the rat brain although there were large regional variations in the density of the fiber networks. When compared with the localization of nitric oxide synthase, it was observed that although nitric oxide-responsive and the nitric oxide-producing structures were found in similar locations in general this distribution was complementary. Only occasionally was nitric oxide-mediated cyclic GMP synthesis observed in structures which also contained nitric oxide synthase. We conclude that the nitric oxide-responsive soluble guanylyl cyclase and nitric oxide synthase are usually juxtaposed at very short distances in the rat brain. These findings very strongly support the proposed role of nitric oxide as an endogenous activator of the soluble guanylyl cyclase in the central nervous system and convincingly demonstrate the presence of the nitric oxide-cyclic GMP signal transduction pathway in virtually every area of the rat brain.

Histology and histochemistry of the aging cerebral cortex: an overview

This review contributes to a new vision of the most important findings in the aging cerebral cortex as elucidated by modern histology and histochemistry. It includes an overview of the macroscopic and microscopic changes involved, not only in normal aging, but also in the main age-related neurodegenerative diseases. Finally, the most accepted theories about aging as well as the implications of nitric oxide in this process are described.

Neuronal and inducible nitric oxide synthase and nitrotyrosine immunoreactivities in the cerebral cortex of the aging rat

Neuronal and inducible nitric oxide synthase (nNOS and iNOS) and nitrotyrosine immunoreactivities were localized and semiquantitatively assessed in the cerebral cortex of aged rats by means of light microscopic immunocytochemistry and Western blotting, using a new series of specific polyclonal antibodies. In the aged rats the strongly nNOS-immunoreactive multipolar neurons found in layers II-VI of the cortex of young rats were seen in similar numbers, but showed varicose, vacuolated, and fragmented processes, with an irregular outline and loss of spines. A large number of more weakly nNOS-positive neurons, characterized by a ring of immunoreactive cytoplasm, and not seen in young rats, were observed in layers II-VI of aged rat cortex. While no iNOS-immunopositive neurons were found in the cortex of young rats, a large number of such neurons appeared throughout the aged rat cortex. Nitrotyrosine-positive cells outnumbered total NOS-positive neurons in the cortex of young rats, but this relation was inverted in the aged rats, although these showed a slight increase in the number and staining intensity of nitrotyrosine-positive cells. Western blots of brain extracts showed a several-fold increase in both nNOS- and iNOS-immunoreactive bands in the aged rat, but a less marked increase in nitrotyrosine-containing proteins. The results suggest that while nNOS and iNOS expression is substantially increased in the aged rat cortex, this is not necessarily accompanied by a proportionate increase in nitric oxide synthesis. The mechanisms underlying the increased expression of nNOS and iNOS, and the functional implications of this increase, require elucidation.

The distribution of nitric oxide synthase-, adenosine deaminase- and neuropeptide Y-immunoreactivity through the entire rat nucleus tractus solitarius: Effect of unilateral nodose ganglionectomy

The present study has employed immunocytochemistry on free-floating sections of adult rat medulla oblongata to characterise the distribution of nitric oxide synthase- (NOS), adenosine deaminase- (ADA) and neuropeptide Y- (NPY) immunoreactivity (IR) throughout the entire rostro-caudal axis of the nucleus tractus solitarius (NTS). In addition, unilateral nodose ganglionectomy was performed in a group of rats to determine whether any observed immunoreactivity was associated with central vagal afferent terminals. NOS-IR was found throughout the entire NTS, in cells, and both varicose and non-varicose fibres. Furthermore, unilateral nodose ganglionectomy resulted in a clear reduction in NOS-IR (visualised with diaminobenzidine) in a highly restricted portion of the ipsilateral medial NTS. Similarly, ADA- and NPY-containing cells, fibres and terminals were also found throughout the adult rat NTS. However, following unilateral nodose ganglionectomy, there was no apparent reduction in either ADA-IR or NPY-IR on the denervated side of the NTS. These data indicate a role for nitric oxide, purines and neuropeptide Y as neuromodulators within the rat NTS, although only nitric oxide appears to be primarily associated with vagal afferent input. Adenosine deaminase and neuropeptide Y-containing neurons appear to be predominantly postsynaptic to vagal input, although their possible association with vagal afferents cannot be completely excluded.

Distribution of catecholaminergic afferent fibres in the rat globus pallidus and their relations with cholinergic neurons

The topographical distribution of catecholaminergic nerve fibres and their anatomical relationship to cholinergic elements in the rat globus pallidus were studied. Peroxidase-antiperoxidase and two-colour immunoperoxidase staining procedures were used to demonstrate tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and choline acetyltransferase (ChAT) immunoreactivities, combined with acetylcholinesterase (AChE) pharmacohistochemistry. TH immunoreactive nerve fibres were seen to enter the globus pallidus from the medial forebrain bundle. The greatest density of such fibres was found in the ventral region of the globus pallidus, which was also characterized by the greatest density of ChAT immunoreactive neurons. TH immunoreactive nerve fibres showed varicose arborizations and sparse boutons, which were occasionally seen in close opposition to cholinergic structures. In all regions of the globus pallidus, there were also larger, smooth TH immunoreactive nerve fibres of passage to the caudate putamen. A smaller number of DBH immunoreactive nerve fibres and terminal arborizations were found in the substantia innominata, internal capsule and in the globus pallidus bordering these structures. A few PNMT immunoreactive nerve fibres in the substantia innominata and internal capsule did not enter the globus pallidus. Electron microscopy revealed TH immunoreactive synaptic profiles in the ventromedial area of the globus pallidus corresponding to the nucleus basalis magnocellularis of Meynert (nBM). These made mainly symmetrical and only a few asymmetrical synaptic contacts with dendrites containing AChE reaction product. The results indicate that cholinergic structures in the nBM are innervated by dopaminergic fibres and terminals, with only a very small input from noradrenergic fibres.

Distribution of nitric oxide synthase in the esophagus of the cat and monkey

The distribution of nitrergic neurons and processes in the esophagus of the cat and monkey was studied by light microscopic immunocytochemistry using a specific antibody against purified rat brain nitric oxide synthase and immunoperoxidase procedures. Immunoreactive nerve fibers were found pervading the myenteric plexus, submucous plexus and plexus of the muscularis mucosae, and particularly in the lower esophagus a few immunoreactive fibers entered the epithelium as free nerve endings, some of which derived from perivascular fibers. In the upper esophagus immunoreactive motor end-plates were found in the striated muscle. Thirty-forty-five percent of neuronal cell bodies found in the intramural ganglia and along the course of nerve fiber bundles were immunoreactive and were of the three morphological types earlier described. In the intramural ganglia immunoreactive nerve fibers formed a plexus in which varicose nerve terminals were in close relation to immunoreactive and non-immunoreactive neurons. The intramural blood vessels that crossed the different layers of the esophageal wall were surrounded by paravascular and perivascular plexuses containing immunoreactive nerve fibers. The anatomical findings suggest that nitric oxide is involved in neural communication and in the control of peristalsis and vascular tone in the esophagus. In the lower esophagus a few nitrergic nerve fibers are anatomically disposed to subserve a sensory-motor function.

Expression of NOS, PSA-N-CAM and S100 protein in the granule cell migration pathway of the adult guinea pig forebrain

To investigate the possible role of nitric oxide (NO) in adult neurogenesis and neuron-glial migration in the rostral migratory stream (RMS), we used a double-labeled immunofluorescence technique together with confocal laser scanning microscopy, and examined the localization of nitric oxide synthase (NOS), the highly polysialylated isoform of neural cell adhesion molecule (PSA-N-CAM), and the astroglial marker in brain, S100 protein (S100), throughout the length of the subependymal layer (SEL) to olfactory bulb (OB) pathway of the adult guinea pig forebrain. Blast-like, beaded, clustered immature cellular elements stained for PSA-N-CAM and those having a typical astrocytic phenotypes positive for S100 protein were densely interlaced throughout the entire length of the SEL. Some S100 positive ependymoglial cells (tanycytes) gave off their basal projections into the closely packed PSA-N-CAM immunopositive clusters in the rostral extension of the subependymal zone (SEZre). The SEL was devoid of NOS immunoreactivity. A dense network of punctate, fenestrated and radially oriented immature cellular elements positive both for NOS and PSA-N-CAM intermingled and overlapped in the inner part of the internal granular layer (IGr), whereas in the outer part, PSA-N-CAM expression gradually diminished and the cells shifted to mature bipolar, spherical or spindle-shaped granule cells with uniform cellular contours, which were exclusively immunopositive for NOS. Radially oriented astroglial phenotypes were intertwined with PSA-N-CAM neuronal clusters in the SEL, and were closely apposed to NOS neuronal elements in the IGr. In summary, these results showed a distinct separation of neurons and glia as revealed by PSA-N-CAM and S100 protein immunostaining, and an inverse spatio-temporal correlation of expression between PSA-N-CAM (immature neuroblasts) and NOS (mature neurons) in the adult guinea pig RMS.

Regional changes of NADPH-diaphorase and neuropeptide Y neurons in the cerebral cortex of aged Fischer 344 rats

This study examined the effects of aging on neuropeptide Y (NPY) and NADPH-diaphorase (NADPH-d)-positive neurons of the cerebral cortex in young (3 months) and aged (24 months) Fischer 344 rats by immunohistochemical and histochemical methods. In the aged group, the number of NPY-immunoreactive (IR)/NADPH-d-positive neurons was not significantly changed in all regions of the cerebral cortex compared to the control group. However, the number of NPY-IR/NADPH-d-negative neurons was significantly decreased in frontal association, primary motor, secondary somatosensory, insular, ectorhinal, perirhinal and auditory cortex in the aged group. In the aged rats, about 5-10% of NPY-IR/NADPH-d-positive neurons were dystrophic and scattered within the cerebral cortex. These results suggested that NPY-IR neurons that do not contain NADPH-d are affected by aging and that aging influences NPY-IR/NADPH-d-negative neurons in a region-specific pattern within the cerebral cortex of rats.

Sustained pharmacological inhibition of nitric oxide synthase does not affect the survival of intrastriatal rat fetal mesencephalic transplants

The objective of the present study was to investigate the potential role of the free radical nitric oxide (NO) in the development of fetal rat mesencephalic neurons grafted in a 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease. First, using nitric oxide synthase (NOS)-immunocytochemistry and reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry, we investigated the presence of the neuronal isoform of NOS (nNOS) in intrastriatal mesencephalic grafts. During the course of the experiment (16 weeks) an increase in the staining intensity and the number of nNOS/NADPH-d positive cells within the grafts was observed, as well as a gradual maturation of dopaminergic neurons. In addition, within both the host striatal and grafted mesencephalic tissue, a NO-dependent accumulation of cyclic guanosine monophosphate (cGMP) was detected, indicating the presence of guanylate cyclase, i.e., the target-enzyme for NO. Secondly, to determine the impact of NO on the survival of grafted dopaminergic neurons, 6-OHDA lesioned rats received mesencephalic grafts and were subsequently treated with the competitive NOS-inhibitor Nomega-nitro-l-arginine methylester (l-NAME). After chronic treatment for 4 weeks, tyrosine hydroxylase immunocytochemistry revealed no apparent differences between the survival of grafted dopaminergic neurons in control- or l-NAME treated animals, respectively. As the maturation of grafted dopaminergic neurons coincides with a gradual increase in the expression of nNOS within the graft and since dopaminergic cell numbers are not changed upon administration of l-NAME, it is concluded that endogenously produced and potentially toxic NO does not affect the survival of grafted fetal dopaminergic neurons.

Effects of L-NAME on cerebral metabolic, vasopressin, oxytocin, and blood pressure responses in hemorrhaged rats

NG-nitro-L-arginine methyl ester (L-NAME; 250 micrograms/5 microliters), an inhibitor of NO synthase, or the vehicle artificial cerebrospinal fluid (aCSF; 5 microliters) was administered intracerebroventricularly to conscious rats hemorrhaged (0.7 ml/min) to a 20% volume depletion. Hypotension was maximal 5 min after hemorrhage ended, with compensatory recovery to basal levels 20 min later, regardless of drug treatment. L-NAME, however, elevated (P < 0.05) blood pressure (vs. aCSF controls) 40-45 min after intracerebroventricular administration. In normovolemic rats, L-NAME produced a significant pressor response and increased plasma levels of vasopressin (VP) and oxytocin (OT). After hemorrhage, both hormone levels increased, but only OT was further enhanced by L-NAME. Thus centrally produced NO tonically inhibits OT and VP secretion under basal normovolemic conditions and selectively inhibits OT release during hypovolemia. Hemorrhage increased the rates of glucose utilization in the neural lobe, indicative of enhanced efferent neural functional activity. L-NAME further enhanced the metabolic activity in the entire hypothalamoneurohypophysial system of hemorrhaged animals. Several other brain structures involved in the regulation of blood pressure and the stress response were also metabolically affected by the hemorrhage and L-NAME.

Brain ANG II and prostaglandins mediate the pressor response after central blockade of nitric oxide synthase

Central inhibition of nitric oxide synthase (NOS) by intracerebroventricular (i.c.v.) administration of NG-nitro-l-arginine methyl ester (L-NAME; 150 microg/5 microl) to conscious rats produced a biphasic pressor response characterized by an initial transient increase within 5 min, and a delayed response starting between 60-90 min. The effect was stereospecific, as D-NAME (250 microg/5 microl) did not modify the resting arterial blood pressure, nor did L-arginine (323 microg/5 microl, i.c.v.), indicating the substrate for NOS is not rate-limiting. Intracerebroventricular pretreatment with losartan (25 microg/5 microl), a non-peptide antagonist of the angiotensin II AT1 receptor subtype, or indomethacin (100 microg/5 microl), a blocker of cyclooxygenase, however, prevented the initial increase in blood pressure without affecting the delayed pressor response. In contrast, neither intravenous losartan (10 mg/kg b.wt) nor prazosin, an alpha1 adrenergic receptor antagonist, at doses of 5 microg/5 microl (i.c.v.) or 0.3 mg/kg b.wt (i.v.) were effective in altering the pressor responses. These results indicate that centrally produced NO maintains the resting arterial blood pressure at least partially through modulation of the brain angiotensin system and prostaglandins.

Nitric oxide control of drinking, vasopressin and oxytocin release and blood pressure in dehydrated rats

Intracerebroventricular (i.c.v.) injection of the inhibitor of NO synthase (NOS), N(G)-nitro-L-arginine methyl ester (L-NAME) (250 microg/5 microL) attenuated the drinking response in rats deprived of water for 24 h. Moreover, oxytocin (OT) levels in plasma increased after 2 min, whereas both oxytocin and vasopressin levels were elevated at 120 min after intracerebroventricular injection. The delayed effect of L-NAME on both hormones was not observed in dehydrated animals allowed to drink water. Blood pressure remained stable after injection of artificial cerebrospinal fluid (aCSF) in dehydrated rats not allowed to drink. In rats having access to water, however, there was an immediate but transient pressor response (0-5 min) with a delayed hypotension from 45 to 120 min. L-NAME consistently increased blood pressure in a biphasic mode, whether the animals drank or not, with an early peak at 5 min that decayed after 15-30 min and a second pressor response beginning at 30-45 min and remaining elevated at 120 min when the experiment ended. These pressor responses were independent of the adrenal glands. Thus, centrally produced nitric oxide facilitates drinking, inhibits release of vasopressin and oxytocin from the magnocellular system, and maintains resting arterial blood pressure in normally hydrated and dehydrated rats.

Neurochemical organization of paratrigeminal nucleus projections to the dorsal vagal complex in the rat

The paratrigeminal nucleus, located in the spinal trigeminal tract rostral to the obex, is important in the integration of visceral and somatosensory afferent information and may modulate autonomic function through its projections to the dorsal vagal complex. Anterograde and retrograde neuroanatomical tracers were used in conjunction with immunohistochemistry to determine the neurochemical organization of the efferent pathway from the paratrigeminal nucleus to the dorsal vagal complex in the rat. Double-labelling studies demonstrated that leu-enkephalin, 28-kDa calbindin, and neuronal nitric oxide synthase were present in neurons in the paratrigeminal nucleus that project to the dorsal vagal complex. The results of this study are consistent with the hypothesis that neurochemically distinct pathways from the paratrigeminal nucleus are involved in the sensory modulation of autonomic function.

Neuronal expression of inducible nitric oxide synthase after oxygen and glucose deprivation in rat forebrain slices

Nitric oxide (NO) overproduction has been postulated to contribute significantly to ischaemia-reperfusion neurotoxicity. Inducible or type II NO synthase (iNOS) synthesizes NO in large quantities for long periods of time. Therefore we investigated the expression and localization of iNOS after oxygen and glucose deprivation in rat forebrain slices. In this experimental model, calcium-independent NOS activity reached a maximum 180 min after the end of a 20 min oxygen-glucose deprivation period. During the same period of time, the calcium-independent activity was absent in control forebrain slices. To test whether this calcium-independent NOS activity was due to the expression of iNOS, the effects of the addition of dexamethasone, cycloheximide and pyrrolidine dithiocarbamate were determined. All of them inhibited the induction of the calcium-independent NOS activity measured in the rat forebrain slices after oxygen and glucose deprivation. Furthermore, oxygen and glucose deprivation caused the expression of the gene encoding iNOS in rat forebrain slices, as assessed by the detection of iNOS message and protein in these samples. A sixfold increase in the iNOS mRNA levels was observed at 180 min and the time-course of the expression of iNOS mRNA was in agreement with the temporal profile of iNOS enzymatic activity. Immunohistochemistry analysis revealed that iNOS was highly expressed in neurones, astrocytes and microglial cells. These results demonstrate for the first time that iNOS is expressed in neurones after oxygen and glucose deprivation, and that this expression occurs in short periods of time. These findings suggest that NO can play an important pathogenic role in the tissue damage that occurs after cerebral ischaemia.

CAPON: a protein associated with neuronal nitric oxide synthase that regulates its interactions with PSD95

Nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS) is important for N-methyl-D-aspartate (NMDA) receptor-dependent neurotransmitter release, neurotoxicity, and cyclic GMP elevations. The coupling of NMDA receptor-mediated calcium influx and nNOS activation is postulated to be due to a physical coupling of the receptor and the enzyme by an intermediary adaptor protein, PSD95, through a unique PDZ-PDZ domain interaction between PSD95 and nNOS. Here, we report the identification of a novel nNOS-associated protein, CAPON, which is highly enriched in brain and has numerous colocalizations with nNOS. CAPON interacts with the nNOS PDZ domain through its C terminus. CAPON competes with PSD95 for interaction with nNOS, and overexpression of CAPON results in a loss of PSD95/nNOS complexes in transfected cells. CAPON may influence nNOS by regulating its ability to associate with PSD95/NMDA receptor complexes.

Precise distribution of neuronal nitric oxide synthase mRNA in the rat brain revealed by non-radioisotopic in situ hybridization

Regional distribution of neurons expressing neuronal nitric oxide synthase mRNA in the rat brain was examined by non-radioisotopic in situ hybridization, using digoxigenin-labeled complementary RNA probes. Clustering of intensely positive neurons was observed in discrete areas including the main and accessory olfactory bulbs, the islands of Calleja, the amygdala, the paraventricular nucleus of the thalamus, several hypothalamic nuclei, the lateral geniculate nucleus, the magnocellular nucleus of the posterior commissure, the superior and inferior colliculi, the laterodorsal and pedunculopontine tegmental nuclei, the nucleus of the trapezoid body, the nucleus of the solitary tract and the cerebellum. Strongly-stained isolated neurons were scattered mainly in the cerebral cortex, the basal ganglia and the brain stem, especially the medulla reticular formation. In the hippocampus, an almost uniform distribution of moderately stained neurons was observed in the granular cell layer of the dentate gyrus and in the pyramidal cell layer of the Ammon's horn, while more intensely stained isolated neurons were scattered over the entire hippocampal region. These observations can serve as a good basis for studies on function and gene regulation of neuronal nitric oxide synthase.

Nitric oxide synthase-expressing neurons are area-specifically distributed within the cerebral cortex of the rat

Neuronal nitric oxide synthase produces nitric oxide, a radical involved in neurotransmission as well as in cytotoxicity during stroke and neurodegenerative diseases. In the adult Wistar rat neuronal nitric oxide synthase-positive neurons are inhomogenously distributed along defined cortical areas, with highest densities (18 cells/mm2) in cingular area 1, piriform cortex, frontal motor area Fr 2 and in the medial visual association area Oc 2MM. A medium packing density of neuronal nitric oxide synthase neurons (10/mm2) characterizes primary sensory areas, whereas retrosplenial cortices contain lowest cell numbers (3-5/mm2). The data suggest that functions of certain cortical areas are more dependent on intracortically produced nitric oxide than others, and that cortical injury may cause more severe nitric oxide related cytotoxicity in areas with higher numbers of neuronal nitric oxide synthase-positive neurons.

Expression of rat cGMP-binding cGMP-specific phosphodiesterase mRNA in Purkinje cell layers during postnatal neuronal development

The cDNA encoding rat cGMP-binding, cGMP-specific phosphodiesterase (cGB-PDE) was isolated from a rat lung cDNA library. Although the deduced amino acid sequence showed 93.4% similarity with that of bovine cGB-PDE, the N-terminal portion of rat cGB-PDE was extremely different from that of bovine. Northern blot analysis indicated that cGB-PDE transcripts in rats were expressed not only in aorta and lung, but also in several other tissues including cerebellum. In situ hybridization analysis demonstrated that cerebellar expression of cGB-PDE was confined to Purkinje cell layers in adult rats. To clarify the role of cGB-PDE in the cerebellum, we investigated expression of cGB-PDE mRNA in rats of various ages. cGB-PDE mRNA was not observed in the cerebellum of newborn rats, but levels of a cGB-PDE mRNA were markedly increased between 4 days and 28 days of age and reached a maximum in eight-week-old rats. In this study, we suggest that cGB-PDE plays important roles not only in regulating the relaxation of vascular vessels, but also in establishing neuronal networks in the cerebellum at an early postnatal stage. In addition the NO/cGMP/cGB-PDE pathway appears to be essential for the induction of long-term depression.

Nitric oxide as a modulator of medullary pathways

1. The present study has employed in vitro electrophysiology and chemical neuroanatomy to determine whether nitric oxide (NO) could be considered a modulator at neurons involved in medullary cardiovascular control pathways. 2. The NO donor diethylamine-NO caused concentration-related depolarizations of the rat isolated nodose ganglion preparation that were sensitive to blockade by inhibitors of soluble guanylate cyclase. 3. Incubation of rat medulla oblongata sections (50 microns) with a polyclonal antibody to NO synthase (NOS) revealed a topographic network of NOS-containing neurons. Specifically, NOS-positive neurons were found throughout the entire rostral-caudal axis of the nucleus tractus solitarius (NTS) and also in the area postrema, dorsal motor nucleus of the vagus, nucleus ambiguous, caudal and rostral ventrolateral medulla, nucleus gigantocellularis and lateral paragigantocellularis. 4. These data indicate that NO has functional actions on centrally projecting rat vagal afferent neurons that ultimately innervate the NTS. Furthermore, neurons that contain the enzyme NOS and that are, therefore, capable of using NO are localized in medullary nuclei concerned with both parasympathetic and sympathetic cardiovascular control pathways.

Aging and the dendritic morphology of the rat laterodorsal and pedunculopontine tegmental nuclei

The morphological appearance and quantitative parameters characterizing the dendrites of NADPH-diaphorase-stained neurons in the laterodorsal (LDT) and pedunculopontine (PPN) tegmental nuclei of 3-, 12- and 26-month-old rats were studied. All dendritic segments were classified according to the number of terminal and link segments they drain and the vertex analysis was used to quantify the dendritic tree and to determine its configuration. Morphological aberrations of the dendrites as local swelling, nodulation, thinning, shrinkage, folding and even the appearance of stumps were observed with advancing age. The quantitative analysis demonstrated a significant reduction (one-way ANOVA) of the total dendritic length, mean terminal path length, maximal segment length, total segment number and number of terminal segments at the rostral two thirds of the LDT and in the PPN. The mean vertex path length and the mean segment length significantly decreased only at the rostral level of the LDT. Plotting of the segment length against equivalent orders showed a decrease in all generations of the dendritic segments. The vertex ratios remained constant and indicated that the configuration of the dendritic tree remained unchanged during aging. The alterations in the dendrites mainly developed after 12 months of age. The age-related changes in the morphology and quantitative parameters of the dendrites in the rostral two thirds of the LDT and PPN were rather similar, which could be explained by the common anatomical, neurochemical and electrophysiological features. Thus, the present results suggest a mild, but continuous regression of the dendritic tree of the rat LDT and PPN in normal aging.

Role of vascular nitric oxide in physiological and pathological conditions

This review describes the ability of certain diseases, such as essential hypertension, atherosclerosis, angina, and vasospasm, to reduce vascular nitric oxide (NO) formation or to increase its metabolism. In contrast, others, such as hypotension, sepsis, stroke, myocardial depression, and inflammatory responses, increase NO synthesis. The mechanism implicated in the changes in the formation and metabolism of NO are described. To prevent or treat these pathological processes, in which a deficiency in vascular NO formation plays a causative role, NO may be provided through methods such as direct NO administration or indirect NO supply through either NO donors or L-arginine, which facilitates NO formation.

The sympathetic nervous system is involved in the maintenance but not initiation of the hypertension induced by N(omega)-nitro-L-arginine methyl ester

Studies in anesthetized animals have advanced the theory that there is an important neurogenic component to the hypertension caused by pharmacological inhibition of nitric oxide, but studies in conscious animals have produced conflicting evidence for and against this theory. To try to reconcile the seemingly contradictory data, we hypothesized that the neurogenic component of this hypertension is time dependent such that the sympathetic nervous system is involved primarily in the maintenance, rather than the initiation, of the hypertension. We measured intra-arterial pressure in conscious, unrestrained rats with and without guanethidine-induced sympathectomy during varying durations of intravenous N(omega)-nitro-L-arginine methyl ester (L-NAME). The major new finding is that sympathectomy had no effect on the hypertensive response to bolus injections of L-NAME but in the same rats it produced a greater than 50% attenuation in the hypertension seen after 6 days of continuous L-NAME (change in mean arterial pressure, 23+/-4 versus 55+/-4 mm Hg, P<.01, sympathectomy versus control). Using 8-hour infusions of L-NAME, we found that 60 minutes was the minimum time required for detecting a sympathectomy-sensitive component of L-NAME-induced hypertension. Furthermore, we demonstrate that the magnitude of this component increases further between 8 hours to 6 days of continuous L-NAME: it accounted for only 18% of the total hypertensive response at 8 hours but 61% after 6 days. From these experiments, we conclude that the importance of the sympathetic system in the pathogenesis of L-NAME-induced hypertension accrues slowly over hours and days, and thus its importance can be overlooked by focusing on the initial phase of the hypertension.

Expression of the calcium-independent cytokine-inducible (iNOS) isoform of nitric oxide synthase in rat placenta

The presence of the calcium-independent cytokine-inducible nitric oxide synthase (iNOS) has been investigated in rat placenta from day 19 of gestation till delivery. iNOS has been detected at the mRNA, enzyme activity and protein levels in complete placenta. Immunocytochemical detection of iNOS was heterogeneously distributed in control placenta. Intraperitoneal injection of pregnant rats at 21 days of gestation with lipopolysaccharide (LPS) increased the iNOS immunoreactivity in the decidua basalis of the placenta, and, when the mRNA levels and enzyme activity were measured in total tissue, a moderate increase (approx. 160%) was observed. A constitutive nuclear factor kappaB activity was observed in placenta from both control and LPS-treated animals. These results indicate constitutive expression of iNOS in rat placenta.

Distribution of neuronal nitric oxide synthase in the rat liver

We studied the distribution of neuronal nitric oxide synthase (nNOS) in the rat liver with a specific polyclonal antibody by using immunocytochemical procedures in the light microscopic level. Immunoreactive varicose nerve fibers were found forming a dense plexus around the interlobular hepatic artery and the interlobular bile duct in the hepatic hilus, and in the hepatic artery ramifications of the portal triads. The density of nNOS positive nerve fibers decreases with successive portal ramifications, and some non-immune positive nerve fibers were found in the distal portions of the arterial vessels. The presence of the nNOS positive nerve fibers suggests that the possible main functional role could be related with the regulation of hepatic blood circulation and hepatobiliary activities.

Neuronal nitric oxide synthase alternatively spliced forms: prominent functional localizations in the brain

Neuronal nitric-oxide synthase (nNOS) is subject to alternative splicing. In mice with targeted deletions of exon 2 (nNOS(delta/delta)), two alternatively spliced forms, nNOS beta and gamma, which lack exon 2, have been described. We have compared localizations of native nNOS alpha and nNOS beta and gamma by in situ hybridization and immunohistochemistry in wild-type and nNOS(delta/delta) mice. To assess nNOS catalytic activity in intact animals we localized citrulline, which is formed stoichiometrically with NO, by immunohistochemistry. nNOS beta is prominent in several brain regions of wild-type animals and shows 2-to 3-fold up-regulation in the cortex and striatum of nNOS(delta/delta) animals. The persistence of much nNOS mRNA and protein, and distinct citrulline immunoreactivity (cit-IR) in the ventral cochlear nuclei and some cit-IR in the striatum and lateral tegmental nuclei, indicate that nNOS beta is a major functional form of the enzyme in these regions. Thus, nNOS beta, and possibly other uncharacterized splice forms, appear to be important physiological sources of NO in discrete brain regions and may account for the relatively modest level of impairment in nNOS(delta/delta) animals.

Nitric oxide and fibroblast growth factor in autonomic nervous system: short- and long-term messengers in autonomic pathway and target-organ control

The freely diffusible messenger nitric oxide (NO), generated by NO synthase (NOS)-containing "nitroxergic" (NO-ergic) neurons, is unique among classical synaptic chemical transmitters because of its "non-specificity", molecular "NO-receptors" (e.g. guanylyl cyclase, iron complexes, nitrosylated proteins or DNA) in target cells, intracellular targeting, regulated biosynthesis, and growth factor/cytokine-dependence. In the nervous system, expression of NOS is particularly intriguing in central and peripheral autonomic pathways and their targets. Here, anatomical and functional links appear to exist between NOS, its associated catalytic NADPH-diaphorase enzyme activity (NOSaD) and fibroblast growth factor-2 (FGF-2), a pleiotropic cytokine with mitogenic actions, suggesting mutual "short- and long-term" actions. Several recent studies performed in the rat sympathoadrenal system, an anatomically and neurochemically well-defined autonomic pathway with target-specific functional units of sympathetic preganglionic neurons (SPNs) in the spinal cord, provide evidence for this hypothesis. The NO and cytokine signals may interact at the level of gene expression, transcription factors, post-transcriptional control or second messenger cross-talk. Thus, unique biological roles of FGF-2 and the NO system are likely to exist in neuroendocrine actions, vasomotory perfusion control as well as in neurotrophic actions in sympathetic innervation of the adrenal gland. In view of their anatomical co-existence, functional interplay and synchronizing effects on neuronal networks, multiple roles are suggested for both "short- and long-term" signalling molecules in neuroendocrine functions and integrated autonomic target organ control.

Subcellular localization of nitric oxide synthase in the cerebral ventricular system, subfornical organ, area postrema, and blood vessels of the rat brain

The distribution of neuronal nitric oxide synthase (nNOS) has been studied in the more rostral portion of the lateral ventricle, subfornical organ, area postrema and blood vessels of the rat central nervous system. nNOS was located by means of a specific polyclonal antibody, by using light and electron microscopy. Light microscopy showed immunoreactive varicose nerve fibers and terminal boutons-like structures in the lateral ventricle, positioned in supra- and subependimal areas. The spatial relationships between immunoreactive neuronal processes and the wall of the intracerebral blood vessels were studied. Electron microscopy showed numerous nerve fibers in the wall of the lateral ventricle; many were nNos-immunoreactive and established very close contact with ependymal cells. Immunoreactive neurons and processes were found in the subependymal plate of the ventricular wall, the subfornical organ, the area postrema, and the circularis nucleus of the hypothalamus. In these last three areas, the immunoreactive neurons were found close to the perivascular space of fenestrated and nonfenestrated blood vessels. The nNOS immunoreactivity was localized to the endoplasmic reticulum, cisterns, ribosomes, neurotubules, and in the inner part of the external membrane. In the terminal boutons, the reaction product was found surrounding the vesicle membranes. This distribution showed nNOS as a predominantly membrane-bound protein. The nitrergic nerve fibers present in the wall of the ventricular system might regulate metabolic functions as well as neurotransmission in the subfornical organ, area postrema and circularis nucleus of the hypothalamus.

Inhibition of gastric acid secretion by stress: a protective reflex mediated by cerebral nitric oxide

Moderate somatic stress inhibits gastric acid secretion. We have investigated the role of endogenously released NO in this phenomenon. Elevation of body temperature by 3 degrees C or a reduction of 35 mmHg (1 mmHg = 133 Pa) in blood pressure for 10 min produced a rapid and long-lasting reduction of distension-stimulated acid secretion in the rat perfused stomach in vivo. A similar inhibitory effect on acid secretion was produced by the intracisternal (i.c.) administration of oxytocin, a peptide known to be released during stress. Intracisternal administration of the NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) reversed the antisecretory effect induced by all these stimuli, an action prevented by intracisternal coadministration of the NO precursor, L-arginine. Furthermore, microinjection of L-NAME into the dorsal motor nucleus of the vagus nerve reversed the acid inhibitory effects of mild hyperthermia, i.v. endotoxin, or i.c. oxytocin, an action prevented by prior microinjection of L-arginine. By contrast, microinjection of L-NAME into the nucleus tractus solitarius failed to affect the inhibitory effects of hyperthermia, i.v. endotoxin, or i.c. oxytocin. Immunohistochemical techniques demonstrated that following hyperthermia there was a significant increase in immunoreactivity to neuronal NO synthase in different areas of the brain, including the dorsal motor nucleus of the vagus. Thus, our results suggest that the inhibition of gastric acid secretion, a defense mechanism during stress, is mediated by a nervous reflex involving a neuronal pathway that includes NO synthesis in the brain, specifically in the dorsal motor nucleus of the vagus.

Presence of nitric oxide synthase activity in roots and nodules of Lupinus albus

NO is a widespread messenger molecule in physiology. We were interested in investigating whether an NO-generating system could be present in plants. NO and L-[14C]citrulline were synthesized by roots and nodules of Lupinus albus in an L-arginine-dependent manner. L-[14C]Citrulline production was inhibited by N(G)-monomethyl-L-arginine, a nitric oxide synthase antagonist, in a competitive way. NADPH-diaphorase activity was localized in the vascular bundles in root and nodules, and also in the nodule infected zone. This staining was significantly reduced in the presence of N(G)-monomethyl-L-arginine. These results indicate the presence of a putative nitric oxide synthase in plants.

NADPH diaphorase activity and nitric oxide synthase immunoreactivity in lordosis-relevant neurons of the ventromedial hypothalamus

The distribution of the enzymes NADPH diaphorase and nitric oxide synthase in the ventromedial nucleus of the hypothalamus of cycling and ovariectomized/estrogen-treated and control female rats was demonstrated using histochemical and immunocytochemical methods. Serial section analysis of vibratome sections through the entire ventromedial nucleus showed that NADPH diaphorase cellular staining was localized primarily in the ventrolateral subdivision. NADPH diaphorase staining was visible in both neuronal perikarya and processes. Light microscopic immunocytochemistry using affinity-purified polyclonal antibodies to brain nitric oxide synthase revealed a similar pattern of labelling within the ventromedial nucleus and within neurons of the ventrolateral subdivision of the ventromedial nucleus. Control experiments involved omitting the primary antibodies; no labelling was visible under these conditions. Some, but not all, neurons in the ventrolateral subdivision of the ventromedial nucleus contained both NADPH diaphorase and brain nitric oxide synthase as demonstrated by co-localization of these two enzymes in individual cells of this area. That NADPH diaphorase and brain nitric oxide synthase were found in estrogen-binding cells was shown by co-localization of NADPH diaphorase and estrogen receptor and brain nitric oxide synthase and estrogen receptor at the light and ultrastructural levels, respectively. Our studies suggest that brain nitric oxide synthase is present and may be subject to estrogenic influences in lordosis-relevant neurons in the ventrolateral subdivision of the ventromedial nucleus. The hypothalamus is a primary subcortical regulatory center controlling sympathetic function. Therefore, not only is nitric oxide likely to be important for reproductive behavior, but also for the regulation of responses to emotional stress and other autonomic functions.

Presence of neuronal nitric oxide synthase in the suprachiasmatic nuclei of mouse and rat

Nitric oxide has recently been identified as a major neural regulator. It is synthesized by the enzyme nitric oxide synthase. Whilst considerable functional evidence has pointed to an involvement of nitric oxide in circadian regulation, all previous morphological studies have failed to demonstrate the presence of nitric oxide synthase in the mammalian suprachiasmatic nucleus. By use of an antibody directed against whole recombinant rat neuronal nitric oxide synthase we have identified the presence of immunoreactivity for this enzyme in the suprachiasmatic nucleus of mouse and rat, to provide the first detailed report of this enzyme in the suprachiasmatic nucleus for any species of mammal. Immunoreactivity for neuronal nitric oxide synthase was found in neurons throughout the suprachiasmatic nucleus of mice and no difference could be detected between the ventrolateral and dorsomedial parts of the nucleus in terms of the optical density of the immunostaining. Very small, rounded neuronal cell bodies were immunopositive. Electron microscopy revealed that these neurons had relatively large nuclei and scant cytoplasm containing relatively few organelles, which sometimes included some 100 nm dense-cored peptidergic vesicles. Only about 5% of such neurons were not detectably immunoreactive. By contrast, in the rat suprachiasmatic nucleus, a much smaller number of neurons were immunopositive and these cells were aggregated in the ventrolateral part of the nucleus. The immunoreactive neurons were bipolar cells with scanty cytoplasm. Electron microscopy revealed diffuse immunoreactivity in the cytosol, but not within any organelles. In the surrounding neuropil immunoreactive dendrites and axons mingled with much larger numbers of immunonegative processes, but immunoreactive boutons were only identified just outside the dorsal margin of the nucleus. Astrocytes, oligodendrocytes and endothelial cells in the suprachiasmatic nucleus were immunonegative. NADPH-diaphorase activity was not detectable in the suprachiasmatic nucleus of either mouse or rat. This morphological evidence for nitric oxide synthase-immunoreactive cells in the suprachiasmatic nucleus supports the existing functional evidence for an involvement of nitric oxide in the transmission of light-induced signals to the suprachiasmatic nucleus in mammals.

Nitric oxide production by brain stem neurons is required for normal performance of eye movements in alert animals

Although nitric oxide (NO) is produced by discrete groups of neurons in the brain, participation of NO in premotor structures directly involved in reflexively evoked, sensory-motor functions has not been demonstrated so far. We now show that NO is a physiological mediator in the generation of a specific motor response in alert behaving animals. In the oculomotor system, numerous neurons expressing nitric oxide synthase (NOS) are located in the prepositus hypoglossi, a nucleus involved in the control of horizontal eye movements. Unilateral inhibition of NOS within this nucleus results in severe ocular nystagmus with slow phases directed to the contralateral side. Accordingly, local increases of NO or cyclic GMP produced a nystagmus in the opposite direction. It is concluded that a balanced production of NO by prepositus hypoglossi neurons is a necessary condition for the normal performance of eye movements in alert animals.

Changes in NADPH-diaphorase neurons of the rat laterodorsal and pedunculopontine tegmental nuclei in aging

The aim of the present study was to compare the morphological pattern and the quantitative parameters of nitric oxide (NO)-containing neurons in the laterodorsal (LTD) and pedunculopontine (PPN) tegmental nuclei of 3-, 12- and 26-month-old rats. NADPH-diaphorase (NADPH-d) histochemical reaction, as a marker of the cholinergic neurons in the two mesopontine nuclei, and computer-assisted image analysis were used. The relationships between the neurons stained for NADPH-d and choline acetyltransferase (ChAT) were examined using a double-labelling procedure. The results demonstrated only occasional ChAT positive somata that did not exhibit NADPH-d staining. The volume of the LTD and PPN and the number of NADPH-d neurons remained unaltered with advancing age. However, ANOVA demonstrated a significant effect of age and level on the cross-sectional areas, maximum diameters and staining intensity of NADPH-d somata in the LTD and PPN. The three parameters were reduced in 26-month-old rats compared to 3-month-old rats. The changes in the morphological appearance of NADPH-d somata and processes as well as the quantitative analysis pointed to age-related neuronal atrophy. It was accompanied by hypertrophy of some neighbouring neurons, suggesting a compensatory mechanism which would counteract the degenerative changes. The age-dependent alterations in the LTD and PPN were rather similar.

Nitric oxide synthase in mating behavior circuitry of male Syrian hamster brain

Chemosensory and hormonal stimuli are essential for mating in the male Syrian hamster. These signals are processed in a neural circuit that includes the medial amygdaloid nucleus (Me), bed nucleus of the stria terminalis (BNST), and medial preoptic area (MPOA). Nitric oxide is implicated in the regulation of male sexual behavior, and nitric oxide synthase (NOS), the enzyme that catalyzes the production of nitric oxide, is present in the limbic system. In this study, the distribution of NOS-containing neurons in mating behavior circuitry of the male Syrian hamster brain was determined using labeling for brain NOS (bNOS) and reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). bNOS and NADPH-d labeled equivalent populations of neurons. NOS-containing neurons were clustered in specific subnuclei with in the Me, BNST, and MPOA. NOS-positive fibers and neurons were seen in the stria terminalis and ventral amygdalofugal pathway, which link the Me with BNST and MPOA. Many NOS-positive neurons in the posterior subdivision of the Me, the medial preoptic nucleus (MPN), and the ventral premammillary nucleus contain androgen receptors. Castration reduced NOS-positive neurons in the MPN, implying a selective regulation of NOS by gonadal steroids. Together, these results suggest that NOS may contribute to the regulation of male sexual behavior by influencing the central neural processing of hormonal and chemosensory signals in the hamster limbic system.

Distribution of nitric oxide synthase-immunoreactive neurons in fetal rat brains at embryonic day 15 and day 19

Although nitric oxide (NO) is hypothesized to play a role in the modelling of neuronal connections in the developing brain, no precise histological information has been reported on nitric oxide synthase immunoreactive (NOS-IR) structures in the embryonic brain. Thus, we examined the distribution of NOS-IR structures in the rat brain at embryonic day 15 (E15) and day 19 (E19), as a stage of early embryonic neurogenesis and active synaptogenesis, respectively. In the brain at E15, a few NOS-IR cell bodies were observed in the diencephalon near the 3rd ventricle and in the pons. By E19, the number of NOS-IR cells was greatly increased. Many NOS-IR cells were distributed throughout the forebrain and the medulla oblongata. NOS-IR cells of the neostriatum were located in its ventrolateral two-thirds. NOS-IR cells in the hypothalamus were distributed densely in the medial part while sparsely in the latero-ventral part, suggesting medio-lateroventral directions of NOS development. In the lower brainstem, on the other hand, NOS-IR cells were distributed in a similar pattern to that reported in adult rat, indicating earlier development of synaptic refinement in this area. The number of NOS-IR cells in the cerebral cortex and the cerebellum was very few.

Effects of the 3',5'-phosphodiesterase inhibitors isobutylmethylxanthine and zaprinast on NO-mediated cGMP accumulation in the hippocampus slice preparation: an immunocytochemical study

The effect of inhibition of 3',5'-phosphodiesterase (PDE) activity on the cGMP accumulation was studied in control and nitric oxide (NO) stimulated hippocampal slices incubated in vitro using immunohistochemical visualisation of cGMP. Isobutylmethylxanthine (IBMX) was used as a non-selective PDE inhibitor and zaprinast was used as a selective inhibitor of cGMP-specific PDE activity. In the absence of PDE inhibitors cGMP-immunoreactivity (cGMP-IR) was found in blood vessel walls only. After incubation with the NO-donor sodium nitroprusside (SNP) cGMP-IR was found in a few isolated varicose fibres which were distributed throughout the slice. Incubation in the presence of either 1 mM IBMX or 10 microM zaprinast resulted in cGMP-IR in small numbers of varicose fibres distributed throughout the hippocampal slice. SNP in combination with IBMX resulted in cGMP-IR in small numbers multitude of varicose fibres throughout the slice; occasionally cell somata were observed. After incubation with SNP and zaprinast cGMP-IR was found in varicose fibres, although with a more restricted distribution and less numerous than in the presence of IBMX. In the latter combination, varicose fibres were observed predominantly in the CA2/CA3 region and in the stratum lacunosum molecular of the hippocampus, and cell somata were occasionally observed throughout the hippocampus. The differential distribution of cGMP-IR in the presence of different PDE inhibitors is consistent with the notion that there are regional differences in the localization of cGMP hydrolyzing enzymes in the hippocampus.

Interleukin-1 beta specifically stimulates nitric oxide production in the hypothalamus

In previous experiments we have shown the role of nitric oxide (NO) in basal and interleukin-1 beta (IL-1 beta)-induced CRH and ACTH release in vitro. Now, we have studied the possible production of NO from hypothalamic cell cultures, particularly after IL-1 beta stimulation or L-NOArg inhibition, by high performance liquid chromatographic (HPLC) assay of L-citrulline production, adding further evidence for a role of NO in IL-1 beta activity in the hypothalamus.

A chromaffin cell-derived protein induces the NADPH-diaphorase phenotype in cultured rat spinal cord neurons

We have recently demonstrated that neurotrophins induce reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity in cultured spinal cord neurons. One prominent neuron population of the spinal cord expressing NADPH-diaphorase activity in vivo are preganglionic sympathetic neurons, including those innervating the adrenal medulla. These neurons receive trophic support from their target. We have shown previously that chromaffin cells contain as yet unidentified neurotrophic molecules, which may include releasable factors relevant for the survival and differentiation of developing preganglionic sympathetic neurons. We have studied the influence of proteins derived from bovine chromaffin cells and released by nicotine on NADPH-diaphorase expression in spinal cord cultures established from 16-day-old rat embryos. At this embryonic age, NADPH-diaphorase activity becomes apparent in the spinal cord and predominantly expressed in sympathetic nuclei. Similar to brain-derived neurotrophic factor and neurotrophin-4, a heat- and trypsin-sensitive component from chromaffin cells contained in granule preparations up-regulated the number of NADPH-diaphorase-positive neurons in spinal cord cultures. Combined application of this activity and neurotrophin-4 resulted in an additive effect, indicating that the effect of the chromaffin cell-derived active component is not mediated by one of the trk B ligands. This was confirmed by co-treatment studies with the trk-signalling pathway inhibitor K252b, which did not inhibit the effect of the chromaffin cell-derived protein(s). Further studies revealed that NADPH-diaphorase reactivity is inducible in spinal cord neurons at any time point throughout the entire culture period of six days, suggesting de novo induction of the enzyme rather than a survival-promoting effect of the activity from chromaffin cells. Culture supernatants from nicotine-stimulated bovine chromaffin cells induced NADPH-diaphorase-positive neurons at the same magnitude as the material obtained from chromaffin granule preparations. Our data suggest that chromaffin cell-derived proteins are capable of up-regulating NADPH-diaphorase activity or to induce de novo this transmitter phenotype in neuron populations of the spinal cord, which may include preganglionic sympathetic neurons.

Prevention by lamotrigine, MK-801 and N omega-nitro-L-arginine methyl ester of motoneuron cell death after neonatal axotomy

Motoneuron cell death was analysed in the rat facial motor nucleus after neonatal facial nerve transection. In situ DNA fragmentation labelling showed that axotomized motoneurons die by an apoptotic mechanism. In order to investigate the existence of excitotoxic mechanisms in this type of neuronal death, rats were treated with several agents known to possess neuroprotective action through a variety of mechanisms. The Na+ channel inhibitor lamotrigine and the antagonist for the N-methyl-D-aspartate-type glutamate receptor, dizocilpine maleate (MK-801) were found to be able to rescue motoneurons from cell death induced by axotomy. The nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester was also able to protect motoneurons from death, but to a lesser extent. The distribution of constitutive and inducible isoforms of nitric oxide synthase was investigated by immunocytochemistry in the facial motor nucleus. No changes were detected in constitutive nitric oxide synthase immunoreactivity in the facial motor nucleus after axotomy. However, in the axotomized facial motor nucleus, inducible nitric oxide synthase showed a positive immunolabelling specifically located in activated astrocytes, but not in microglia. Nitric oxide derived from activated astrocytes may have a role in promoting excitotoxic mechanisms in axotomized motoneurons. We conclude that excitotoxic mechanisms involving apoptotic cell death are present when immature motoneurons die as a consequence of target disconnection.

Correlation between brain nitric oxide synthase activity and opiate withdrawal

The opiate withdrawal induced by administration of naloxone to morphine-dependent mice correlates with an increment of calcium- dependent nitric oxide synthase (NOS) activity in the cerebellum. L-NAME, an irreversible competitive inhibitor of NOS (0.5, 5, 25, 50 mg/kg) injected sc. 45 min. prior to naloxone significantly reduced the number of escape jumps and other motor symptoms of abstinence. In addition, L-NAME also decreased NOS activity in cerebellum. L-arginine, but not D-arginine, when coadministered with L-NAME, prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals. These results demonstrate a hyperactivity of the L-arginine: NO pathway in opiate withdrawal and suggests the possibility of a therapeutic use of NOS inhibitors in this state.