The correlation between neuron counts and optical density of NADPH-diaphorase histochemistry in the rat striatum: a quantitative study

Impaired expression of neuronal nitric oxide synthase in the gracile nucleus is involved in neuropathic changes in Zucker Diabetic Fatty rats with and without 2,5-hexanedione intoxication

These studies examined the influence of 2,5-hexanedione (2,5-HD) intoxication on expression of neuronal nitric oxide synthase (nNOS) in the brainstem nuclei in Zucker Diabetic Fatty (ZDF) vs. lean control (LC) rats. Functional neuropathic changes were also investigated following axonal damage and impaired axonal transport induced by the treatment. Animals were intoxicated by i.p. injection of 2,5-HD plus unilateral administration of 2,5-HD over the sciatic nerve. The mechanical thresholds and withdrawal latencies to heat and cold stimuli on the foot were measured at baseline and after intoxication. The medulla sections were examined by nNOS immunohistochemistry and NADPH-diaphorase histochemistry at the end of the treatments. The mechanical thresholds and withdrawal latencies were significantly decreased while nNOS immunostained neurons and NADPH-diaphorase positive cells were selectively reduced in the gracile nucleus at baseline in ZDF vs. LC rats. NADPH-diaphorase reactivity and nNOS positive neurons were increased in the ipsilateral gracile nucleus in LC rats following 2,5-HD intoxication, but its up-regulation was attenuated in ZDF rats. These results suggest that diabetic and chemical intoxication-induced nNOS expression is selectively reduced in the gracile nucleus in ZDF rats. Impaired axonal damage-induced nNOS expression in the gracile nucleus is involved in neuropathic pathophysiology in type II diabetic rats.

Nitric Oxide-Soluble Guanylyl Cyclase-Cyclic GMP Signaling in the Striatum: New Targets for the Treatment of Parkinson's Disease?

Striatal nitric oxide (NO)-producing interneurons play an important role in the regulation of corticostriatal synaptic transmission and motor behavior. Striatal NO synthesis is driven by concurrent activation of NMDA and dopamine (DA) D1 receptors. NO diffuses into the dendrites of medium-sized spiny neurons which contain high levels of NO receptors called soluble guanylyl cyclases (sGC). NO-mediated activation of sGC leads to the synthesis of the second messenger cGMP. In the intact striatum, transient elevations in intracellular cGMP primarily act to increase neuronal excitability and to facilitate glutamatergic corticostriatal transmission. NO–cGMP signaling also functionally opposes the inhibitory effects of DA D2 receptor activation on corticostriatal transmission. Not surprisingly, abnormal striatal NO–sGC–cGMP signaling becomes apparent following striatal DA depletion, an alteration thought to contribute to pathophysiological changes observed in basal ganglia circuits in Parkinson's disease (PD). Here, we discuss recent developments in the field which have shed light on the role of NO–sGC–cGMP signaling pathways in basal ganglia dysfunction and motor symptoms associated with PD and l-DOPA-induced dyskinesias.

Adult brain nitrergic activity after concomitant prenatal exposure to ethanol and methyl mercury

Pregnant rats were exposed to ethanol (EtOH) and/or methyl mercury (MeHg) during fetal brain development. Nitrergic activity was quantified by densitometric measurement of formazan deposits in the hippocampus, cerebellum and striatum of two-month-old offspring following histochemical assay for NADPH-diaphorase (NADPH-d) activity. Compared to control subjects, an increase in nitrergic activity was found in the molecular layer of dentate gyrus and in the lacunosum molecular and stratum radiatum of CA1 (cornus amoni 1) in the EtOH+MeHg group, whereas a single administration of EtOH increased the activity in all striatal segments. The cerebellum seems to be less sensitive at this time-point to intoxication, and presented an increase only at the molecular layer of EtOH-exposed animals when compared to the MeHg and EtOH+MeHg groups (ANOVA, one-way followed by Tukey's test, p<0.05 or p<0.01). Taken together, results suggest that developmental exposure to EtOH and MeHg, singularly or in combination, alters nitrergic activity in adult rat in different ways depending on the region and layer of the central nervous system (CNS), and that these alterations might be related to different local metabolic properties.

Impact of dopamine-glutamate interactions on striatal neuronal nitric oxide synthase activity

RATIONALE

It is known that dopamine (DA) D1 receptor activation stimulates striatal nitric oxide (NO) synthesis, whereas D2 receptor activation produces the opposite effect. However, the mechanisms involved in the dopaminergic modulation of nitric oxide synthase (NOS) are unknown.

OBJECTIVES

We hypothesized that the effects of DA on striatal NO signaling are dependent on ongoing glutamatergic activation of NOS. Therefore, the current study examined whether intact N-methyl-D-aspartic acid (NMDA) receptor activation is required for the dopaminergic modulation of NOS activity.

METHODS

We assessed the impact of pharmacological manipulations of D1, D2, and NMDA receptors on NOS activity in the dorsal striatum and motor cortex using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Drugs were administered systemically to conscious animals and NADPH-d staining was quantified in these regions using ex vivo measurements of tissue optical density.

RESULTS

Administration of the neuronal NOS inhibitor N (G)-propyl-L-arginine (NPA), the D1 receptor antagonist SCH 23390, and the NMDA receptor antagonist 3-phosphonopropyl-piperazine-2-carboxylic acid (CPP) all attenuated staining selectively in the striatum. Administration of the D2 receptor agonist quinpirole decreased NADPH-d staining in both the striatum and cortex. Striatal NADPH-d staining elicited by administration of the D1 receptor agonist SKF 81297 or the D2 receptor antagonist eticlopride was attenuated by NPA, SCH 23390, and CPP pretreatment. Quinpirole pretreatment also abolished the facilitatory effect of SKF 81297.

CONCLUSIONS

These studies show for the first time that ongoing NMDA receptor activation is necessary for the modulation of striatal NOS activity by both facilitatory (D1 receptor activation) and inhibitory (D2 receptor activation) dopaminergic signaling mechanisms.

Electroacupuncture decreases nitric oxide synthesis in the hypothalamus of spontaneously hypertensive rats

Acupuncture-related effects on autonomic function have been explored via biological and neurophysiologic studies. The hypothalamus, known to regulate the autonomic nervous system, is likely affected by acupuncture treatment that modulates sympathetic functions. The aim of this study was to investigate the effect of electroacupuncture at the Jogsamni point (ST36, an acupoint known to modulate autonomic function) on expression of neuronal nitric oxide synthase (nNOS) in the hypothalamus of spontaneously hypertensive rat. Nitric oxide, which is produced by nNOS activity, plays an important role in the regulation of many physiologic processes, including sympathetic activities, in the hypothalamus and other parts of the brain. nNOS expression was assessed by immunohistochemistry of nNOS and histochemistry of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d). The staining intensities of nNOS-positive neurons and NADPH-d-positive neurons were quantitatively assessed using microdensitometry to measure changes in optical density. The results show that electroacupuncture at ST36 reduced the expression and activity of nNOS in the hypothalamus of spontaneously hypertensitive rats. These findings suggest that the electroacupuncture at ST36 results in modulation of the activity of nNOS in the hypothalamus of spontaneously hypertensive rat.

NADPH-diaphorase histochemical changes in the hippocampus, cerebellum and striatum are correlated with different modalities of exercise and watermaze performances

Nitric oxide is involved in memory and motor learning. We investigated possible influences of exercise on spatial memory and NADPH-diaphorase (NADPH-d) histochemical activity in the hippocampus, striatum and cerebellum. Fifteen albino Swiss mice between the 22nd and 55th post-natal days were exercised in the following modalities: voluntary (V), acrobatic (A), acrobatic/voluntary (AV) and forced (F) and compared to inactive group (I). After the exercise period, all subjects were tested in the water maze for 3 days. Animal brains were processed for NADPH-d histochemistry. Densitometry of the neuropil of the hippocampus, striatum and cerebellum and morphometric analysis of NADPHd+ type I neurons of the striatum were done. Exercise groups presented higher levels of NADPH-d activity in the molecular and polymorphic layers of dentate gyrus and lacunosum molecular layer of CA1. The A group presented higher NADPH-d activity in the cerebellar granular layer than all other groups. Branching points and dendritic segment densities of NADPH-d type I neurons were higher in V, A and AV than in F and I groups. Exercise groups revealed best performances on water maze tests. Thus, different modalities of exercise increases in different proportions for the nitrergic activity in the hippocampus, striatum and cerebellum, and these changes seem to be beneficial to spatial memory.

Responses of neuronal nitric oxide synthase expression in the brainstem to electroacupuncture Zusanli (ST 36) in rats

Recent studies have reported that l-arginine-derived nitric oxide (NO) in the gracile nucleus modifies the hypotensive responses to electroacupuncture (EA) stimulation of Zusanli (ST 36). The purpose of this study was to examine the influence of EA stimulation of ST 36 on neuronal NO synthase (nNOS) expression in the brainstem nuclei in rats. EA stimulation of ST 36 and a non-acupoint was performed using 3 Hz of stimulation for 10 s every 2 min for a period of 120 min in rats anesthetized with ketamine. Rats in the sham-treated group received surgery and EA needles were placed into the acupoints without performing the stimulation. After 2-h stimulation and sham treatment, animals were perfused with 4% paraformaldehyde. Sections of rat medulla were examined by immunolabeling with a polyclonal antibody directed against nNOS. The brainstem nuclei were also visualized by NADPH-diaphorase histochemistry, a marker of nNOS activity. nNOS expression and NADPH-diaphorase reactivity were quantified by using a microscope with reticule grid to count the number of positive cells over a nucleus. Unilateral EA stimulation of ST 36 in rats caused increases in nNOS immunostained cells in the rostral region of the ipsilateral gracile nucleus, but was not altered in the contralateral gracile nucleus compared with sham-treated rats (P < 0.05, n = 6-7). NADPH-diaphorase-positive cells were also increased in the ipsilateral gracile nucleus of rats with EA stimulation. nNOS immunostaining and NADPH-diaphorase-positive neurons were significantly increased in both ipsilateral and contralateral sides of the medial nucleus tractus solitarius (mNTS) in rats receiving EA ST 36 compared with sham-treated animals (P < 0.05). nNOS immunostaining and NADPH-diaphorase reactivity was neither altered in the gracile nucleus and mNTS of non-acupoint stimulated rats nor other brainstem nuclei in rats with EA ST 36. These results show that nNOS immunoreactivity and NADPH-diaphorase reactivity are consistently increased in the gracile nucleus and the mNTS by EA ST 36. We conclude that EA ST 36 induces nNOS expression in the gracile nucleus and mNTS, and enhanced nNOS-NO in the nuclei may modify central cardiovascular regulation, which contribute to hypotensive effects of acupuncture.

Responses of nitric oxide synthase expression in the gracile nucleus to sciatic nerve injury in young and aged rats

Neuronal nitric oxide synthase (nNOS) is induced in dorsal root ganglion neurons following axotomy in young rats, and is also increased in the gracile nucleus neurons of intact aged rats. The present study examined the influence of sciatic nerve axotomy on nNOS expression in the gracile nucleus in young compared to aged rats. The unilateral transection of the sciatic nerve was performed in young (4 months) and old (24 months) Fischer rats. Sections of rat medulla obtained 14 days after axotomy were immunolabelled using a polyclonal antibody directed against nNOS and stained by nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry, a marker of nNOS activity. In young rats, unilateral axotomy produced increased NADPHd containing neurons in the rostral region and the caudal region of the ipsilateral gracile nucleus compared to the side with intact sciatic nerve. In old rats, the NADPHd containing neurons in the ipsilateral gracile nucleus were moderately increased by axotomy over the age changes seen in the contralateral side. Similar results were obtained with nNOS immunoreactivity in young rats, but more cells were seen with NADPHd staining compared to nNOS immunostaining in old rats. The results suggest that unilateral sciatic axotomy causes an increase in nNOS expression in the ipsilateral gracile nucleus of young rats, which is still seen in old rats as an increase over normal aging changes.

Neuronal nitric oxide synthase is resistant to ethanol

To test for a possible role of nitric oxide (NO) in the neurotoxicity of ethanol, we studied the effects of ethanol on the neuronal NO synthase (nNOS) both in vitro and in vivo. Ethanol, up to 200 mM, did not change the NOS activity in the cerebellar homogenate or the production of NO by the cultured cerebellar granule cells. The number of NADPH diaphorase-positive cells in the culture did not change after the exposure to 200 mM ethanol in vitro. The NOS activity in the various brain regions of mice remained similar to the controls after the acute (3 g/kg) and the chronic (33 g/kg/day, 3.5 days) administration of ethanol. N(omega)-nitro-L-arginine, a NOS inhibitor, did not affect the ethanol-withdrawal behavior. These results indicate that nNOS is resistant to ethanol at clinically relevant concentrations and that ethanol affects the NO-operated system in the brain through a pathway other than that of nNOS.

Immune stress activates putative nitric oxide-producing neurons in rat brain: cumulative effects with restraint

Immune and restraint stresses induce changes in the hypothalamo-pituitary-adrenal axis activity and autonomic function. In the hypothalamus, the paraventricular nucleus (PVN) plays an integral role, and nitric oxide (NO) is hypothesized to participate in this process. We used 1) intravenous injections of lipopolysaccharide (LPS, 125 microg/kg) to identify activated (Fos-positive) putative NO-producing neurons, 2) retrograde tracing to determine if autonomic medullary regions signal the PVN to mediate this activation, and 3) intravenous LPS injections plus restraint stress to determine if responses to restraint are altered by the presence of immune stress. At 2 hours after LPS injections, approximately 15% of putative NO-producing neurons were activated in the nucleus of the tractus solitarius (NTS) and ventrolateral medulla (VLM); about half of the putative NO neurons in the PVN were activated. In LPS + restraint rats, the percentage of activated putative NO neurons in the PVN was not significantly different from LPS-treated rats, but the numbers of putative NO neurons and activated NO neurons per section increased significantly. Retrogradely labeled neurons were found mostly in the middle NTS and VLM, and about 75% were activated. No neurons in the NTS or VLM were triple labeled. The results show that putative NO-producing neurons in the PVN, NTS, and VLM are activated by circulating LPS. However, the LPS-induced signaling to the PVN likely occurs through pathways other than the NO network of neurons in NTS or VLM. Finally, superimposition of restraint stress onto animals already exposed to immune stress stimulates the NO system in the PVN to a greater extent than either stress alone.

Central terminals of orofacial primary afferents and NADPH-diaphorase activity in the trigemino-solitary complex of rats

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity and the central terminal fields of branches of the mandibular and chorda tympani nerves were visualized histochemically at the same time using transganglionic transport of wheat germ agglutinin conjugated with horseradish peroxidase. The blue NADPH-d-positive neurons comprised a sparse network in the dorsomedial spinal trigeminal subnucleus oralis and a dense one in the rostral lateral division of the nucleus of the solitary tract. In the subnucleus caudalis, most labeled neurons were in the superficial zone, and smaller numbers were in the magnocellular zone. The NADPH-d-positive neurons in the subnucleus oralis and the nucleus of the solitary tract overlapped mostly with the transganglionically labeled terminal field from the lingual nerve, partly with the terminal field from the inferior alveolar and chorda tympani nerves, and rarely with the terminal field from the mental nerve. The NADPH-d-positive neurons in the dorsomedial paratrigeminal nucleus and subnucleus caudalis overlapped mostly with the terminal field from the lingual nerve, partly with the terminal field from the inferior alveolar and mental nerves and never with the terminal field from the chorda tympani. A statistically significant reduction in the number of NADPH-d-positive neurons was seen bilaterally in subnucleus oralis and the nucleus of the solitary tract when the lingual nerve was transected. Inflammatory insults to the lingual nerve or tooth pulps significantly increased the number of NADPH-d-positive neurons in subnucleus oralis, the nucleus of the solitary tract, and subnucleus caudalis. These results show that the NO/cyclic GMP system in the trigeminal and solitary nuclei is differentially regulated trans-synaptically by trigeminal afferents depending on the nucleus and sensory modality.

Dynamic changes in NADPH-diaphorase staining reflect activity of nitric oxide synthase: evidence for a dopaminergic regulation of striatal nitric oxide release

In fixed tissue, neuronal NADPH-diaphorase staining results from nitric oxide synthase (NOS) activity. Neuronal NOS only synthesizes nitric oxide once activated by the binding of Ca2+/calmodulin. We show here that neuronal NADPH-diaphorase staining is also dependent on Ca2+/calmodulin, implying that only activated NOS is detected. In addition, in bovine pulmonary endothelial cells, carbachol and bradykinin dramatically and rapidly increase the intensity of NADPH-diaphorase staining. Furthermore, administration of MK801, an NMDA antagonist, decreases neuronal NADPH-diaphorase staining. This suggests that the intensity of the NADPH-diaphorase staining is related to the level of enzyme activation at the moment of tissue fixation. The potential of exploiting this observation to detect cellular activation of NOS is illustrated by the observations that the intensity of NADPH-diaphorase staining in rat striatal neurones is decreased following systemic treatment with the D1-like dopamine receptor antagonist SCH23390, and increased by the D2-like antagonist eticlopride. These results therefore provide strong evidence that the NADPH-diaphorase reaction can be used to monitor NOS activity at a cellular level of resolution, and reveal a dopaminergic regulation of NOS activity in the striatum mediated by D1-like and D2-like dopamine receptors.

Nitric oxide participates in the stimulatory and neurotoxic action of endothelin on rat striatal dopaminergic neurons

1. Our method of real-time monitoring of dopamine release from rat striatal slices revealed that endothelin (ET)-3-induced dopamine release was inhibited by NG-methyl-L-arginine (L-NMMA; 1 mM), an inhibitor of nitric oxide (NO) synthase, while NG-methyl-D-arginine (D-NMMA; 1 mM), an inactive isomer of L-NMMA, had no effect. 2. The inhibition of L-NMMA (0.1 mM) became apparent when tissues were pretreated with tetrodotoxin (1 microM) for 30 min and subsequently exposed to ET-3 (4 microM). 3. L-NMMA (0.1 and 1 mM) dose dependently protected against ET-3-triggered hypoxic/hypoglycemic impairment of striatal responses to high K+. 4. Thus, NO may work as a promoter in mediation of the stimulatory and neurotoxic action of ET-3 on the striatal dopaminergic system, presumably by interacting with interneurons in the striatum.

Nitric oxide producing neurons in the human colon: an immunohistochemical and histoenzymatical study

The nitric oxide producing neurons of the human colonic myenteric plexus have been studied by using antibodies against cerebellar NO synthase type I (NOS-IR) and NADPH-diaphorase (NAPDH-d) histoenzymatic reaction. The majority of the stained neurons were both NOS-IR and NADPH-d-positive, while a few others were either NADPH-d-positive or NOS-IR only. Among the co-stained neurons, four subpopulations sharing various degrees of staining intensities have been identified. These findings indicate that in the human colon a one-to-one correlation between NOS-IR and NADPH-d positivity does not exist and thus the NADPH-d reaction does not delineate with certainty all NO-producing neurons. The degree of staining intensity might account for different intracellular amounts of these two enzymes.