Nitric Oxide Synthase Interneurons Research Articles

Amperometric measurements of cocaine cue and novel context-evoked glutamate and nitric oxide release in the nucleus accumbens core.

Cue-induced reinstatement of cocaine seeking after self-administration (SA) and extinction relies on glutamate release in the nucleus accumbens core (NAcore), which activates neuronal nitric oxide synthase interneurons. Nitric oxide (NO) is required for structural plasticity in NAcore medium spiny neurons, as well as cued cocaine seeking. However, NO release in the NAcore during reinstatement has yet to be directly measured. Furthermore, the temporal relationship between glutamate release and the induction of an NO response also remains unknown. Using wireless amperometric recordings in awake behaving rats, we quantified the magnitude and temporal dynamics of novel context- and cue-induced reinstatement-evoked glutamate and NO release in the NAcore. We found that re-exposure to cocaine-conditioned stimuli following SA and extinction increased extracellular glutamate, leading to release of NO in the NAcore. In contrast, exposing drug-naïve rats to a novel context led to a lower magnitude rise in glutamate in the NAcore relative to cue-induced reinstatement. Interestingly, novel context exposure evoked a higher magnitude NO response relative to cue-induced reinstatement. Despite differences in magnitude, novel context evoked-NO release in the NAcore was also temporally delayed when compared to glutamate. These results demonstrate a dissociation between the magnitude of cocaine cue- and novel context-evoked glutamate and NO release in the NAcore, yet similarity in the temporal dynamics of their release. Together, these data contribute to a greater understanding of the relationship between glutamate and NO, two neurotransmitters implicated in encoding the valence of distinct contextual stimuli.

A Dopamine–Acetylcholine Cascade: Simulating Learned and Lesion-Induced Behavior of Striatal Cholinergic Interneurons

The giant cholinergic interneurons of the striatum are tonically active neurons (TANs) that respond with pauses to appetitive and aversive cues and to novel events. Whereas tonic activity emerges from intrinsic properties of these neurons, glutamatergic inputs from intralaminar thalamic nuclei and dopaminergic inputs from midbrain are required for genesis of pause responses. No prior computational models encompass both intrinsic and synaptically gated dynamics. We present a mathematical model that robustly accounts for behavior-related electrophysiological properties of TANs in terms of their intrinsic physiological properties and known afferents. In the model, balanced intrinsic hyperpolarizing and depolarizing currents engender tonic firing and glutamatergic inputs from thalamus (and cortex) both directly excite and indirectly inhibit TANs. If this inhibition, probably mediated by GABAergic nitric oxide synthase interneurons, exceeds a threshold, a persistent K+ conductance current amplifies its effect to generate a prolonged pause. Dopamine (DA) signals modulate both the intrinsic mechanisms and the external inputs of TANs. Simulations revealed that many learning-dependent behaviors of TANs, including acquired pauses to task-relevant cues, are explicable without recourse to learning-dependent changes in synapses onto TANs, due to a tight coupling between DA bursts and TAN pauses. These interactions imply that reward-predicting cues often cause striatal projection neurons to receive a cascade of signals: an adaptively scaled DA burst, a brief acetylcholine (ACh) burst, and an ACh pause. A sensitivity analysis revealed a unique TAN response surface, which shows that DA inputs robustly cooperate with thalamic inputs to control cue-dependent pauses of ACh release, which strongly affects performance- and learning-related dynamics in the striatum.

Specific Subtypes of Cortical GABA Interneurons Contribute to the Neurovascular Coupling Response to Basal Forebrain Stimulation

Neurovascular coupling, or the tight coupling between neuronal activity and regional cerebral blood flow (CBF), seems largely driven by the local processing of incoming afferent signals within the activated area. To test if cortical gamma-aminobutyric acid (GABA) interneurons-the local integrators of cortical activity-are involved in this coupling, we stimulated the basalocortical pathway in vivo, monitored cortical CBF, and identified the activated interneurons (c-Fos-immunopositive) and the neuromediators involved in this response. Basal forebrain (BF) stimulation induced ipsilateral increases in CBF and selective activation of layers II to VI somatostatin- and/or neuropeptide Y-containing, as well as layer I GABA interneurons. Nitric oxide synthase interneurons displayed weak bilateral activation, whereas vasoactive intestinal polypeptide- or acetylcholine (ACh)-containing GABA interneurons were not activated. Selective cholinergic deafferentation indicated that ACh released from stimulated BF afferents triggered the CBF response, but the latter was mediated, in part, by the local release of GABA from cholinoceptive cortical interneurons, and through GABA-A receptor-mediated transmission. These data show that activation of specific subsets of GABA interneurons and their GABA-A-mediated effects on neuronal, vascular, and/or astroglial targets are necessary for the full expression of the hemodynamic response to BF stimulation. Further, these findings highlight the importance of understanding the cellular networks and circuitry that underlie hemodynamic signals, as only specific subsets of neurons may be activated by a given stimulus, depending on the afferent inputs they receive and integrate.

Nucleus accumbens nitric oxide immunoreactive interneurons receive nitric oxide and ventral subicular afferents in rats

The nitric oxide generating neurons of the nucleus accumbens exert a powerful influence over striatal function, in addition, these nitrergic inputs are in a position to regulate the dopaminergic and glutamatergic inputs on striatal projection neurons. It was the aim of this study to establish the source of the glutamatergic drive to nitric oxide synthase interneurons of the nucleus accumbens. The nucleus accumbens nitric oxide-generating neurons receive asymmetrical, excitatory, presumably glutamatergic inputs. Possible sources of these inputs could be the limbic and cortical regions known to project to this area. To identify sources of the excitatory inputs to the nitric oxide synthase-containing interneurons of the nucleus accumbens in the rat we first examined the ultrastructural morphology of asymmetrical synaptic specializations contacting nitric oxide synthase-immunohistochemically labeled interneurons in the nucleus accumbens. Neurons were selected from different regions of the nucleus accumbens, drawn using camera lucida, processed for electron microscopic analysis, and the boutons contacting nitric oxide synthase-labeled dendrites were photographed and correlated to the drawings. Using vesicle size as the criterion the source was predicted to be either the prefrontal cortex or the ventral subiculum of the hippocampus. To examine this prediction, a further study used anterograde tracing from both the prefrontal cortex and the ventral subiculum, and nitric oxide synthase immunohistochemistry with correlated light and electron microscopy. Based on appositions by anterogradely labeled fibers, selected nitric oxide synthase-labeled neurons within the nucleus accumbens, were examined with electron microscopic analysis. With this technique we confirmed the prediction that subicular afferent boutons make synaptic contact with nitric oxide synthase interneurons, and demonstrated anatomically that nitric oxide synthase boutons make synaptic contact with the dendritic arbors of nitric oxide synthase interneurons. We suggest that the subicular input may excite the nitric oxide synthase neurons synaptically, while the nitric oxide synthase–nitric oxide synthase interactions underlie a nitric oxide signaling network which propagates hippocampal information, and expands the hippocampus’s influence on ‘gating’ information flow across the nucleus accumbens.

Basal forebrain nitric oxide synthase (NOS)-containing neurons project to microvessels and NOS neurons in the rat neocortex: cellular basis for cortical blood flow regulation.

Stimulation of basal forebrain neurons results in local increases in cortical cerebral blood flow that are dependent upon cholinergic and nitrergic mechanisms. In the present study, we investigated the possibility that basal forebrain nitric oxide synthase (NOS)-containing neurons project to microvessels and NOS interneurons in the rat cerebral cortex. We performed quisqualic (QUIS) acid lesions of the basal forebrain and evaluated their effects on cortical NOS immunostained nerve terminals, with emphasis on those associated with microvessels and NOS interneurons, both at the light and/or electron microscopic levels. The results show that basal forebrain NOS neurons provide about one third of the overall cortical NOS innervation. Further, the data indicate that basalocortical NOS fibres establish privileged associations with microvessels and NOS neurons, as respective denervations of 60 and 45% were observed following lesion. At the electron microscopic level, most perivascular NOS neuronal elements corresponded to nerve terminals and a majority ( approximately 25%) of these were located in the immediate vicinity of the blood vessels, similar to the perivascular distribution reported previously for classic neurotransmitters/neuromediators. NOS terminals abutting on cortical NOS neurons were primarily nonjunctional. Altogether, these results raise the possibility that not only cholinergic but also nitrergic basal forebrain neurons are involved in the flow response observed following stimulation of the basal forebrain. Further, they suggest interactions between basalocortical and intracortical NOS neurons. We conclude that these interactions are involved in the spatial and temporal regulation of cortical perfusion following basal forebrain activation, and that they may become dysfunctional in pathologies such as Alzheimer's disease which affects both the basal forebrain and the cortical NOS neurons.

α-Actinin-2 in rat striatum: localization and interaction with NMDA glutamate receptor subunits

Alpha-actinin (α-actinin-2) is a protein which links the NR1 and NR2B subunits of N-methyl- d-aspartate (NMDA) glutamate receptors to the actin cytoskeleton. Because of the importance of NMDA receptors in modulating the function of the striatum, we have examined the localization of α-actinin-2 protein and mRNA in striatal neurons, and its biochemical interaction with NMDA receptor subunits present in the rat striatum. Using an α-actinin-2-specific antibody, we found intense immunoreactivity in the striatal neuropil and within striatal neurons that also expressed parvalbumin, calretinin and calbindin. Conversely, α-actinin-2 immunoreactivity was not detected in neurons expressing choline acetyltransferase and neuronal nitric oxide synthase. Dual-label in situ hybridization revealed that the highest expression of α-actinin-2 mRNA is in substance P-containing striatal projection neurons. The α-actinin-2 mRNA is also present in enkephalinergic projection neurons and interneurons expressing parvalbumin, choline acetyl transferase and the 67-kDa isoform of glutamic acid decarboxylase, but was not detected in somatostatin-expressing interneurons. Immunoprecipitation of membrane protein extracts showed that α-actinin-2 is present in heteromeric complexes of NMDA subunits, but is not associated with AMPA receptors in the striatum. A subunit-specific anti-NR1 antibody co-precipitated major fractions of NR2A and NR2B subunits, but only a minor fraction of striatal α-actinin-2. Conversely, α-actinin-2 antibody immunoprecipitated only modest fractions of striatal NR1, NR2A and NR2B subunits. These data demonstrate that α-actinin-2 is a very abundant striatal protein, but exhibits cellular specificity in its expression, with very high levels in substance-P-containing projection neurons, and very low levels in somatostatin and neuronal nitric oxide synthase interneurons. Despite the high expression of this protein in the striatum, only a minority of NMDA receptors are linked to α-actinin-2. This interaction may identify a subset of receptors with distinct anatomical and functional properties.

Nitric oxide synthase interneurons in the monkey cerebral cortex are subsets of the somatostatin, neuropeptide Y, and calbindin cells

Neuronal nitric oxide synthase (nNOS) is expressed most densely in two types of cortical interneurons. Large nitric oxide (LNOS) interneurons express dense somatostatin- and neuropeptide Y-immunoreactivity, whereas small (SNOS) interneurons are calbindin-immunoreactive. We used double labeling methods in several areas of the monkey cerebral cortex to determine how precisely these neurochemical labels define the two types of nNOS interneurons. The LNOS cells were essentially always (>99%) immunoreactive for somatostatin and neuropeptide Y, but did not express calbindin. The LNOS cells comprised about 30% of the somatostatin cells and about 60% of the neuropeptide Y cells. The SNOS cells were nearly always (87–98%) calbindin-immunoreactive, and were rarely or never labeled with antibodies to somatostatin or neuropeptide Y. The SNOS cells accounted for about 20% of all of the calbindin cells. The findings demonstrate that the two types of nNOS cells can be distinguished by antibodies to calbindin, somatostatin and neuropeptide Y, but none of these markers is found exclusively in nNOS cells. Nevertheless, neuropeptide Y-immunoreactivity provides a useful marker for LNOS cells, because it is very dense in these cells and only light in the interneurons that lack nNOS.

Localization of alternatively spliced NMDAR1 glutamate receptor isoforms in rat striatal neurons

Alternative splicing of the mRNA encoding the N-methyl-D-aspartate (NMDA) receptor subunit NR1 changes the structural, physiologic, and pharmacologic properties of the resultant NMDA receptors. We used dual label immunocytochemistry and confocal microscopy to localize the four alternatively spliced segments of the NR1 subunit (N1, C1, C2, and C2') in rat striatal neurons. Striatofugal projection neurons and four populations of interneurons were studied. Projection neurons, which were identified by immunolabeling for calbindin and by retrograde tracing from the globus pallidus and the substantia nigra, were the only striatal neurons containing C1 segment immunoreactivity. Projection neurons were also C2 segment immunopositive, as were all other neuronal populations studied. Projection neurons were C2' segment immunonegative. In contrast, each of the interneuron types were labeled by the antibody to the C2' segment: nitric oxide synthase interneurons were labeled intensely, calretinin and parvalbumin neurons were labeled moderately strongly, and cholinergic neurons were also labeled but less strongly than the other types of interneurons. Parvalbumin interneurons showed distinct N1 segment immunolabeling, which was not found in other types of striatal neurons. Our results suggest that all striatal neurons studied synthesize NR1 subunit proteins, but the isoforms of the protein present in projection neurons and the several types of interneurons are distinct. This differential expression of NR1 isoforms may affect both neuronal function and selective vulnerability of neurons to injury.

Localization of alternatively spliced NMDAR1 glutamate receptor isoforms in rat striatal neurons

Alternative splicing of the mRNA encoding the N-methyl-D-aspartate (NMDA) receptor subunit NR1 changes the structural, physiologic, and pharmacologic properties of the resultant NMDA receptors. We used dual label immunocytochemistry and confocal microscopy to localize the four alternatively spliced segments of the NR1 subunit (N1, C1, C2, and C2′) in rat striatal neurons. Striatofugal projection neurons and four populations of interneurons were studied. Projection neurons, which were identified by immunolabeling for calbindin and by retrograde tracing from the globus pallidus and the substantia nigra, were the only striatal neurons containing C1 segment immunoreactivity. Projection neurons were also C2 segment immunopositive, as were all other neuronal populations studied. Projection neurons were C2′ segment immunonegative. In contrast, each of the interneuron types were labeled by the antibody to the C2′ segment: nitric oxide synthase interneurons were labeled intensely, calretinin and parvalbumin neurons were labeled moderately strongly, and cholinergic neurons were also labeled but less strongly than the other types of interneurons. Parvalbumin interneurons showed distinct N1 segment immunolabeling, which was not found in other types of striatal neurons. Our results suggest that all striatal neurons studied synthesize NR1 subunit proteins, but the isoforms of the protein present in projection neurons and the several types of interneurons are distinct. This differential expression of NR1 isoforms may affect both neuronal function and selective vulnerability of neurons to injury. J. Comp. Neurol. 415:204–217, 1999. © 1999 Wiley-Liss, Inc.

Analysis of connections between nitric oxide synthase neurons in the myenteric plexus of the guinea-pig small intestine.

In the myenteric plexus of the guinea-pig ileum, a sub-population of descending interneurons contains nitric oxide synthase. Final neurons in descending motility pathways, inhibitory circular muscle motor neurons, also contain nitric oxide synthase. In this study we used ultrastructural immunocytochemistry to determine whether nitric oxide synthase descending interneurons provide inputs to all nitric oxide synthase neurons. The presence of nitric oxide synthase inputs to 35 nitric oxide synthase nerve cells from three animals was examined. Nine nerve cells from one ganglion were studied in serial section. Every nerve cell received inputs (close contacts and synapses) from nitric oxide synthase terminals. The number of inputs to the nine serially sectioned neurons ranged from 13 to 45. The inputs were found in about equal numbers on the cell bodies and the dendrites. There was no significant correlation between the size of nitric oxide synthase neurons and the number of nitric oxide synthase inputs they received. There was also no correlation between the number of nitric oxide synthase inputs and the number of 5-hydroxytryptamine inputs (determined in a previous study) received by nitric oxide synthase neurons. Random sections through an additional 26 nitric oxide synthase neurons (seven in the same ganglion and 19 from another two myenteric ganglia from different animals) were examined and nitric oxide synthase synapses and close contacts were observed on each neuron. Nitric oxide synthase interneurons and motor neurons are morphologically indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)