Reduced nicotinamide adenine dinucleotide phosphate-diaphorase/nitric oxide synthase profiles in the human hippocampal formation and perirhinal cortex

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-stained profiles were evaluated throughout the human hippocampal formation (i. e., dentate gyrus, Ammon's horn, subicular complex, entorhinal cortex) and perirhinal cortex. NADPH-d staining revealed pleomorphic cells, fibers, and blood vessels. Within the entorhinal and the perirhinal cortices, darkly stained (type 1) NADPH-d pyramidal, fusiform, bipolar, and multipolar neurons with extensive dendrites were scattered mainly within deep layers and subjacent white matter. Moderately stained (type 2) NADPH-d round or oval neurons were seen mainly in layers II and III of the entorhinal and perirhinal cortices, in the dentate gyrus polymorphic layer, in the CA fields stratum pyramidal and radiatum, and in the subicular complex. The distribution of type 2 cells was more abundant in the perirhinal cortex compared to the hippocampal formation. Lightly stained (type 3) NADPH-d pyramidal and oval neurons were distributed in CA4, the entorhinal cortex medial subfields, and the amygdalohippocampal transition area. Sections concurrently stained for NADPH-d and nitric oxide synthase (NOS) revealed that all type 1 neurons coexpressed NOS, whereas types 2 and 3 were NOS immunonegative. NADPH-d fibers were heterogeneously distributed within the different regions examined and were frequently in close apposition to reactive blood vessels. The greatest concentration of fibers was in layers III and V–VI of the entorhinal and perirhinal cortices, dentate gyrus polymorphic and molecular layers, and CA1 and CA4. A band of fibers coursing within CA1 divided into dorsal and ventral bundles to reach the presubiculum and entorhinal cortex, respectively. Although the distribution of NADPH-d fibers was conserved across all ages examined (28–98 years), we observed an increase in the density of fiber staining in the aged cases. These results may be relevant to our understanding of selective vulnerability of neuronal systems within the human hippocampal formation in aging and in neurodegenerative diseases. © 1995 Wiley-Liss, Inc.     

一氧化氮／一氧化氮合酶与神经创伤

一氧化氮是一种简单的气体分子,可在哺乳类神经细胞内经一氧化氮合酶作用产生。ＮＯ在神经创伤修复中的多重作用近年来已受到越来越多的重视。本文对ＮＯ／ＮＯＳ与神经创伤和再生之间的关系作一综述。     

Adrenalectomy increases reduced nicotinamide adenine dinucleotide phosphate-diaphorase activity in the rat spinal trigeminal subnucleus caudalis

Neurons exhibiting reduced nicotinamide adenine dinucleotide phosphate-diaphorase activity (NADPHd) were quantified at 500 μm rostrocaudal intervals in spinal trigeminal nucleus (Vsp) of adenalectomized (ADX), ADX + corticosterone, and sham-ADX rats 6–12 days after surgery. NADPHd neurons were found predominantly in Vsp subnucleus caudalis (Vc) and in dorsomedial subnucleus oralis. ADX significantly increased the number of NADPHd neurons in superficial laminae of Vc, an effect reversed by chronic corticosterone replacement. ADX effects on NADPHd in superficial laminae of Vc but not in deep laminae of Vc or in the periobex region of Vsp paralleled previously observed sites of ADX enhancement of noxious stimulus-induced Fos-like immunoreactivity. The results indicate that chronic changes in adrenal steroid status regulate NADPHd, a mechanism that may both derive from changes in nitric oxide synthase expression and influence the processing of nociceptive information by central trigeminal neurons.     

Prenatal development of nicotinamide adenine dinucleotide phosphate-diaphorase activity in the human hippocampal formation

Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry was used to study the development of the neurons metabolizing nitric oxide in the prenatal human hippocampal formation. Strongly reactive non-pyramidal neurons appeared in small numbers in the subplate at 15 weeks, and rapidly increased in this layer, as well as the cortical plate—derived layers between 17 and 24 weeks. The marginal zone also had a few NADPH-d cells at 15 weeks. The pattern of these darkly reactive cells stabilized by 28 weeks, with the somata distributed mostly at the border of the cortex and white matter in the entorhinal cortex and subiculum, or the alveus in Ammon's horn. Moderately stained non-pyramidal neurons appeared in the dentate gyrus by 17 weeks, and increased in this region and Ammon's horn up to 28 weeks. Small, lightly reactive non-pyramidal neurons were first seen by 32 weeks and increased in number by term. They were mainly distributed in layers II/III of the entorhinal cortex and stratum pyramidale of the subiculum and Ammon's horn. NADPH-d positive fibers in the marginal zone were mostly thin and developed between 20 and 28 weeks. In other cortical layers, thick processes from the darkly stained NADPH-d neurons appeared first, then fine fibers appeared more numerous, especially after 28 weeks. NADPH-d processes that arose from non-pyramidal cells were frequently apposed to blood vessels, including those in the hippocampal fissure. In addition, NADPH-d reactivity was also present in pyramidal and granule cells, but this staining was most pronounced between 15 and 24 weeks. The results show three types of distinctly stained NADPH-d interneurons in the fetal human hippocampal formation with different developmental courses and morphology. Also, hippocampal principal neurons transiently express NADPH-d at early fetal ages. Our data correlated with other findings suggest that nitric oxide may play a role in neuronal development in the hippocampal formation by modulating neuronal differentiation and maturation, and regulating blood supply. Hippocampus 7:215–231, 1997. © 1997 Wiley-Liss, Inc.     

Topographical distribution of reduced nicotinamide adenine dinucleotide phosphate-diaphorase in the brain of the Japanese quail

The distribution of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity was histochemically investigated in the Japanese quail brain. This enzyme is now considered responsible for the synthesis of nitric oxide, a novel neural messenger whose distribution has not been described in the avian brain until now. The histochemical technique provides a simple and reliable method for staining selected populations of neurons throughout the avian brain. In the telencephalon several regions showed heavily stained NADPH-diaphorase positive neurons and processes. In particular the paleostriatal-paraolfactory lobe complex showed the greatest presence of both positive cells and processes. Neurons and processes were also observed in several regions of the hyperstriatum as well as in the archistriatal nucleus taeniae. Some regions, such as the ectostriatum and the hippocampus, had no positive elements. In the diencephalon, the magnocellular hypothalamic system, which in mammals shows NADPH-diaphorase activity, did not show any particular accumulation of reaction product. On the contrary, retinorecipient areas, such as the visual suprachiasmatic nucleus and the lateral geniculate complex, displayed a composite structure of both positive neurons and processes. The brainstem revealed a large NADPH-diaphorase positive population extending through the tegmental nuclei to the locus coeruleus and subcoeruleus. A complex organization was also observed in the optic lobe, where fusiform elements were distributed within the stratum griseum and superficialis of the tectum. In the medulla, a dense terminal field was observed at the level of the nucleus of the solitary tract, whereas scattered neurons were located within the reticular nuclei. Although the staining of neurons and tracts was highly selective, the positive cells did not correspond to any single known neurotransmitter, neuropeptide, or neuroactive molecule system. Several sensory pathways were heavily stained for the NADPH-diaphorase, including part of the olfactory, visual, and auditory pathways. The findings of the present study reveal that the NADPH-diaphorase-containing systems in the avian brain are organized according to a pattern comparable, because of its complexity, to that observed in mammals. However, important interspecific differences suggest that this novel neural system might be involved in diverse tasks. © 1994 Wiley-Liss, Inc.     

Reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry in the pontomesencephalic region of the human brainstem

Reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-diaphorase), which is specifically localized in neurons, has been histochemically demonstrated in human brain by using a perfusion-fixation procedure. With such fixed human brainstem, it was possible to study the topographic organization of NADPH-diaphorase-containing neurons that were visualized in fine detail for the first time. In the pontomesencephalic region, positive neurons were observed in nuclei around the decussation and arm of the superior cerebellar peduncle. These nuclei included the pedunculopontine tegmental, lateral parabrachial and oral pontine reticular nuclei. The positive somata were mainly multipolar in shape and medium to large in size. The positive neurons appeared to correspond to cholinergic neurons, at least partly in the brainstem, in terms of both the patterns of distribution and the cellular morphology.     

Spatiotemporal pattern of nicotinamide adenine dinucleotide phosphate-diaphorase reactivity in the developing central nervous system of premetamorphic Xenopus laevis tadpoles

We have catalogued the progressive appearance of putative nitric oxide synthase (NOS)-containing neurons in the developing central nervous system (CNS) of Xenopus laevis. Xenopus embryos and larvae were processed in wholemount and in cross section using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry as a marker for NOS within the CNS. The temporal sequence of NADPH-d reactivity identified discrete groups and subgroups of neurons in the forebrain, midbrain, and hindbrain on the basis of their morphology, location, and order of appearance during development. A proportion of these groups of neurons appeared to be important in sensory processing and motor control. Staining also appeared at specific stages in the spinal cord, the retina, and the skin. After the appearance of labelling, NADPH-d reactivity continued in each of the cell groups throughout the stages examined. We found no evidence for staining that subsequently disappeared at later stages in any cell group, indicating a persistent rather than transient role for NO in the Xenopus tadpole CNS. These results are discussed in light of recent findings on possible roles for NADPH-d-positive cell groups within the developing motor circuitry.     

Localization of nicotinamide adenine dinucleotide phosphate-diaphorase reactivity and nitric oxide synthase immunoreactivity in the lumbosacral dorsal root ganglia in guinea pigs

This study examined the distribution of reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) reactivity and nitric oxide synthase (NOS) immunoreactivity in the lumbosacral dorsal root ganglia (DRG) in male guinea pigs. A differential distribution of NADPH-d reactivity and NOS immunoreactivity was detected in neurons of DRG at different segmental levels. There were numerically more intensely stained NADPH-d and NOS reactive cells in the rostral (L1-L3) DRG compared with those at the caudal (L6-S4) levels. In the corresponding DRG, NADPH-d reactivity was not paralleled by NOS immunoreactivity. This was evidenced by the wide distribution of afferent neurons in the lumbosacral DRG stained for NADPH-d, yet only a small number of them exhibited NOS immunoreactivity. Double labelling study has shown that some of the NADPH-d positive neurons were NOS negative. Ultrastructurally, NADPH-d reaction product was associated with the membranes of various subcellular organelles, including the rough endoplasmic reticulum (rER), Golgi saccules, mitochondria and some segments of the nuclear envelop, whereas NOS immune-precipitate was patchily distributed throughout the cytoplasm. Present results suggest that nitric oxide (NO) may function as a neurotransmitter in the afferent pathways at lumbosacral segments. On the other hand, in view of their marked disparity in numbers and the lack of total one-to-one correspondence, it seems likely that the NOS positive neurons represent only a subpopulation of the NADPH-d positive cells in the lumbosacral DRG.     

Nitric oxide synthase in cerebral ischemia

The results of our continuing studies on the role of nitric oxide (NO) in cellular mechanisms of ischemic brain damage as well as related reports from other laboratories are summarized in this paper. Repetitive ip administration ofN ^G-nitro-L-arginine (L-NNA), a NO synthase (NOS) inhibitor, protected against neuronal necrosis in the gerbil hippocampal CA1 field after transient forebrain ischemia with a bell-shaped response curve, the optimal dose being 3 mg/kg. Repeated ip administration of L-NNA also mitigated rat brain edema or infarction following permanent and transient middle cerebral artery (MCA) occlusion with a U-shaped response. The significantly ameliorative dose-range and optimal dose were 0.01–1 mg/kg and 0.03 mg/kg, respectively. Studies using a NO-sensitive microelectrode revealed that NO concentration in the affected hemisphere was remarkably increased by 15–45 min and subsequently by 1.5–4 h after MCA occlusion. Restoration of blood flow after 2 h-MCA occlusion resulted in enhanced NO production by 1–2 h after reperfusion. Administration of L-NNA (1 mg/kg, ip) diminished the increments in NO production during ischemia and reperfusion, leading to a remarkable reduction in infarct volume. In brain microvessels obtained from the affected hemisphere, Ca²⁺-dependent constitutive NOS (cNOS) was activated significantly at 15 min, and Ca²⁺-independent inducible NOS (iNOS) was activated invariably at 4 h and 24 h after MCA occlusion. Two hour reperfusion following 2 h-MCA occlusion caused more than fivefold increases in cNOS activity with no apparent alterations in iNOS activity. Thus, we report here based on available evidence that there is good reason to think that NOS activation in brain microvessels may play a role in the cellular mechanisms underlying ischemic brain injury.     

Expression of three forms of nitric oxide synthase in peripheral nerve regeneration

Nitric oxide (NO) is a short‐lived molecule with messenger and cytotoxic functions in nervous, cardiovascular, and immune systems. Nitric oxide synthase (NOS), the enzyme responsible for NO synthesis, exists in three different forms: the neuronal (nNOS), present in discrete neuronal populations; the endothelial (eNOS), present in vascular endotheliun, and the inducible isoform (iNOS), expressed in various cell types when activated, including macrophages and glial cells. In this study, we have investigated the possible involvement of NO in Wallerian degeneration and the subsequent regeneration occurring after sciatic nerve ligature, using histochemistry and immunocytochemistry for the three NOS isoforms, at different postinjury periods. Two days after lesion, the three NOS isoforms are overexpressed, reaching their greatest expression during the second week. nNOS is upregulated in dorsal root ganglion neurons, centrifugally transported and accumulated in growing axons. eNOS is overexpressed in vasa nervorum of the distal stump and around ligature, and iNOS is induced in recruited macrophages. These findings indicate that different cellular sources contribute to maintain high levels of NO at the lesion site. The parallelism between NOS inductions and well‐known repair phenomena suggests that NO, acting in different ways, may exert a beneficial effect on nerve regeneration. J. Neurosci. Res. 55:198–207, 1999. © 1999 Wiley‐Liss, Inc.     

Differences in peripheral nerve degeneration/regeneration between wild-type and neuronal nitric oxide synthase knockout mice

Nitric oxide (NO), a unique biological messenger molecule, is synthesized by three isoforms of the enzyme NO synthase (NOS) and diffuses from the site of production across cellular membranes. A postulated role for NO in degeneration and regeneration of peripheral nerves has been explored in a sciatic nerve model comparing wild-type mice and mice lacking neuronal NOS after transection and microsurgical repair. In NOS knockout mice, regenerative delay was observed, preceded by a decelerated Wallerian degeneration (WD). In the regenerated nerve, pruning of uncontrolled sprouts was disturbed, leading to an enhanced number of axons, whereas remyelination seemed to be less affected. Delayed regeneration was associated with a delayed recovery of sensor and motor function. In such a context, possible NO targets are neurofilaments and myelin sheaths of the interrupted axon, filopodia of the growth cone, newly formed neuromuscular endplates, and Schwann cells in the distal nerve stump. The results presented suggest that 1) local release of NO following peripheral nerve injury is a crucial factor in degeneration/regeneration, 2) success of fiber regeneration in the peripheral nervous system depends on a regular WD, and 3) manipulation of NO supply may offer interesting therapeutic options for treatment of peripheral nerve lesions.     

Nitric oxide synthase and growth-associated protein are coexpressed in primary sensory neurons after peripheral injury

A possible role for nitric oxide in growth and regeneration of dorsal root ganglion (DRG) afferents has been explored in lesion experiments by comparing immunocytochemistry for nitric oxide synthase (NOS) with that for the growth-associated phosphoprotein 43 (GAP-43). Sciatic nerve ligature induced a progressive increase in the number of small DRG cell profiles immunopositive for NOS between 2 days and 4 weeks of survival. In the proximal stump of the ligature, NOS-immunopositive fibers began to appear 2 days after injury and their growth cones were especially evident after 7 days. NOS-immunopositive fibers appeared past (i.e., distal to) the ligature at 14 days of survival and extended for at least 6 mm in either direction 4 weeks after the lesion. Dorsal root ligature alone at L4–L5 did not result in expression of NOS in DRG neurons or in the appearence of NOS-immunopositive fibers. In rats with dorsal root ligature and nerve ligature, the results were similar to those with nerve ligature only. DRG cell profiles immunopositive for GAP-43 kept increasing from 2 days to 4 weeks after sciatic nerve ligature and included small neurons initially and large neurons subsequently. Numerous axons became GAP-43 immunopositive on both sides of the ligature from 2 days after injury. In double-labeled material, about 80% of DRG cell profiles immunopositive for NOS were also immunopositive for GAP-43. The two antigens co-occurred in peripheral nerve axons proximal to the ligature starting at about 7 days and distal to it at about 2 weeks after ligature. Thus, in response to nerve lesion, nitric oxide may not only provide an injury signal to the central nervous system but may also contribute to the growth and regeneration of injured axons. J. Comp. Neurol. 404:64–74, 1999. © 1999 Wiley-Liss, Inc.     

Differential expression of Fos protein after transection of the rat infraorbital nerve in the trigeminal nucleus caudalis

To determine the effects of nerve injury on Fos expression, temporal and spatial distributions of Fos-positive neurons in the trigeminal nucleus caudalis were examined after tissue injury for isolation of the infraorbital nerve as controls and transection of this nerve as well as noxious chemical stimulation by formalin injection in adult rats. Fos immunoreactivity was markedly elevated in laminae I and II of the only ipsilateral nucleus caudalis 2 h after these surgical procedures and noxious chemical stimulation. The distributions of Fos-positive neurons were restricted rostro-caudally following formalin injection and tissue injury compared to transection of the infraorbital nerve. One day after tissue injury and nerve transection, however, Fos-positive neurons were distributed bilaterally in laminae III and IV extending rostro-caudally and medio-laterally in this nucleus, and this persisted over the 2-week study period. The number of Fos-positive neurons in the side ipsilateral to nerve transection was markedly less than that in the contralateral side whereas positive neurons in the tissue injured rats were distributed symmetrically along the rostro-caudal axis. There was no difference in the contralateral sides between nerve transection and tissue injury groups. The rostro-caudal level showing reduction in Fos expression corresponded roughly to the sites of central termination of the injured nerve in this nucleus, suggesting a role for the primary afferents in the reduction of Fos expression in laminae III and IV neurons of the ipsilateral nucleus caudalis.     

Nitric oxide synthase activity in human pituitary adenomas

OBJECTIVES: The purpose of the present study was to examine human pituitary adenomas for nitric oxide synthase (NOS) activity by immunohistochemical and enzymatic methods. MATERIALS AND METHODS: Adenomatous tissue from 16 patients were obtained during operation and stained immunohistochemically for hormone production and for the three NOS isoenzymes. Cell types that expressed NOS immunoreactivity (IR) were identified, and the NOS isoform was noted. NOS activity was measured enzymatically by the conversion of L-arginine to L-citrulline in tissue samples. RESULTS: Endothelial cells of pituitary adenomas showed increase of eNOS IR compared with control tissue. The nNOS and iNOS IR were the same in adenomas and controls. There was no correlation between NOS IR and NOS activity measured enzymatically and the endocrine activity of the tumour or other clinical variables. CONCLUSION: The observation of increased eNOS IR in endothelial cells of adenomas may suggest that NO plays a role in the regulation of blood flow in pituitary adenomas.     

Postnatal development of nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons in the retina of the golden hamster

The histochemical method was used to investigate the postnatal development of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) -positive neurons in retinas of the golden hamster. NADPH-d-positive neurons were discernible in the retina at postnatal day (P)1. From P4 onward to adulthood, when the retina acquired its laminated characteristics, NADPH-d- positive neurons were observed in the inner nuclear layer (INL) and the ganglion cell layer (GCL). Results showed that NADPH-d-positive neurons in INL and GCL followed different time courses and patterns in their development. NADPH-d-positive neurons in INL underwent a sharp increase from P4 to P8 (3.6-fold), followed by a decrease to 46% of the maximum at P12. This value was maintained relatively constant to the adult level. The mean diameters of NADPH-d-positive neurons in INL, which were smaller than those in the GCL for all ages, increased from P8 to P12 and from P20 to adulthood. As for neurons in the GCL, the increase in cell number was not so apparent for the earlier postnatal days until P20; thereafter, an obvious increase to the adult level was observed. The mean diameters of the NADPH-d-positive cell bodies in the GCL increased with age, except for P16-P20, during which time there was a slight and insignificant decrease. The tendency of changes in cell density was basically similar to that of the total number for both the INL and the GCL. Between P12 and P20, the density distribution map of the NADPH-d-positive neurons underwent dramatic changes: The highest density shifted from the upper central retina at the earlier postnatal days to the lower central retina in the adult. The two waves of increase in NADPH-d-positive neurons coincide with the process of axonal elongation and synaptogenesis and the acquisition of visual function and experience. It is suggested that these NADPH-d-positive neurons are related to these two developmental events.     

Nitric oxide involvement in the trigeminal hyperalgesia in diabetic rats

Trigeminal hyperalgesia frequently appears in diabetic neuralgia altering the transmission of orofacial sensory information. This study was designed to explore the effects of trigeminal hyperalgesia in streptozotocin-induced diabetes monitoring the expression of nitric oxide synthase in the trigeminal ganglion cells. The threshold to heat noxious stimuli decreased in diabetic animals. The number of NADPH-diaphorase (NADPH-d)-positive neurons significantly decreased in the diabetic rats compared with controls. Insulin treatment prevented the decreased nociceptive threshold and reduction of the number of NADPH-d-positive neurons. These findings point out that there is a relationship between the trigeminal nociceptive perception and NADPH-d neuronal expression suggesting that NO may play a role in the pathogenesis of trigeminal sensory neuropathy.     

Nitric oxide and nitric oxide synthase in Huntington's disease

Nitric oxide (NO) is a biologically active inorganic molecule produced when the semiessential amino acid l-arginine is converted to l-citrulline and NO via the enzyme nitric oxide synthase (NOS). NO is known to be involved in the regulation of many physiological processes, such as control of blood flow, platelet adhesion, endocrine function, neurotransmission, neuromodulation, and inflammation, to name only a few. During neuropathological conditions, the production of NO can be either protective or toxic, dependent on the stage of the disease, the isoforms of NOS involved, and the initial pathological event. This paper reviews the properties of NO and NOS and the pathophysiology of Huntington's disease (HD). It discusses ways in which NO and NOS may interact with the protein product of HD and reviews data implicating NOS in the neuropathology of HD. This is followed by a synthesis of current information regarding how NO/NOS may contribute to HD-related pathology and identification of areas for potential future research.     

Nitric oxide in the rat cerebellum after hypoxia/ischemia

Nitric oxide is a regulatory biological substance and an important intracellular messenger that acts as a specific mediator of various neuropathological disorders. In mammals and invertebrates, nitric oxide is synthesized from L-arginine in the central and peripheral neural structures by the endothelial, neuronal and inducible enzymatic isoforms of nitric oxide synthase. Nitric oxide may affect the function of various neurotransmitter-specific systems, and is involved in neuromodulation, reproductive function, immune response, and regulation of the cerebral blood circulation. This makes nitric oxide the main candidate in brain responses to brain ischemia/hypoxia. The cerebellum has been reported to be the area of the brain that has the highest nitric oxide synthase activity and the highest concentration of glutamate and aspartate. By glutamate receptors and physiological action of nitric oxide, cyclic guanisine-5'-monophosphate may be rapidly increased. The cerebellum significantly differs with respect to ischemia and hypoxia, this response being directly related to the duration and intensity of the injury. The cerebellum could cover the eventual need for nitric oxide during the hypoxia, boosting the nitric oxide synthase activity, but overall ischemia would require de novo protein synthesis, activating the inducible nitric oxide synthase to cope with the new situation. The specific inhibitors of nitric oxide synthesis show neuroprotective effects.     

Nitric oxide synthase inhibition and MPTP-induced toxicity in the common marmoset

Nitric oxide, produced following activation of N-methyl-D-aspartate (NMDA) receptors, may be involved in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity since NMDA receptor antagonists have been shown to prevent MPTP induced nigral cell loss in primates. Common marmosets were treated with either saline or MPTP or L-N^Gnitro arginine methyl ester (L-NAME) or MPTP and L-NAME. MPTP-treated common marmosets showed motor deficits including bradykinesia, rigidity, and tremor accompanied by a marked loss of tyrosine hydroxylase-immunoreactive neurones in the substantia nigra pars compacta and of [³H]-mazindol binding in the caudate-putamen. MPTP treatment also caused an increase in glial fibrillary acidic protein (GFAP) staining in the substantia nigra compared to controls. However, MPTP treatment did not alter the number of constitutive nitric oxide synthase-immunoreactive neurones in the caudate-putamen. Furthermore, neurones or glial cells immunoreactive for inducible nitric oxide synthase were not observed in the substantia nigra pars compacta following MPTP treatment. L-NAME treatment alone did not produce any behavioural changes in marmosets and did not alter the number of tyrosine hydroxylase-immunoreactive cells in the substantia nigra pars compacta, the number of constitutive nitric oxide synthase-immunoreactive neurones or [³H]-mazindol binding in the caudate-putamen compared to saline-treated control animals. Furthermore, L-NAME did not affect the motor deficits, loss of tyrosine hydroxylase-immunoreactive neurones in the substantia nigra pars compacta, loss of [³H]-mazindol binding in the caudate-putamen, or the increase in GFAP staining in the substantia nigra induced by MPTP treatment of common marmosets. The failure of L-NAME to protect against MPTP-induced toxicity in the marmoset suggests that nitric oxide does not play a major role in such toxicity and casts doubt over the involvement of the NMDA:nitric oxide system in neurodegeneration in MPTP-treated primates. Synapse 26:301–316, 1997. © 1997 Wiley-Liss, Inc.