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PubMed2004

Postnatal development of cholinergic synapses on mouse spinal motoneurons.

Following birth, when mammals are relatively immobile, significant development of the motor system facilitates weight bearing and locomotion. Prominent cholinergic C-terminals develop on somata and proximal dendrites of spinal motoneurons during this time period. It is hypothesized that these terminals are essential in regulating motoneuron excitability and thus their development contributes to motor system maturation. Therefore, the development of pre- and postsynaptic components of the C-terminal synapse on motoneurons in mice during the early postnatal period was investigated. Fluorescence immunohistochemical studies revealed that developmental increases in punctate labeling of presynaptic cholinergic terminals, as visualized by vesicular acetylcholine transporter immunoreactivity (VAChT-IR) corresponded to the progressive expression and spatial restriction of immunoreactivity for the calcium channel subunit alpha(1)2.2 (N-type) located presynaptically and the muscarinic type 2 acetylcholine receptor situated postsynaptically. In addition, clustering of immunoreactivity for the potassium channel subunit K(V)2.1 occurred within the early postnatal period in concert and colocalized with the maturation of the C-terminals. The time course of development of these components of the C-terminal synapse corresponds to the maturation of the motor system that enables the animal to locomote in an adult-like fashion.

Acetylcholine↗
PubMed2004

Parvalbumin is expressed in glutamatergic and GABAergic corticostriatal pathway in mice.

The connections between the cortex and the striatum are critically involved in control and execution of voluntary movements. Here we focused on the expression of calcium binding protein parvalbumin (PV) in the corticostriatal pathway. Injections of Fluorogold into the striatum gave rise to retrograde labeling of PV-positive neurons in the retrosplenial cortex and somatosensory cortex. The PV-positive corticostriatal projection neurons were mainly found in layer V, but occasionally seen in layers II, III, and VI. The PV immunoreactivity of retrogradely labeled cells was weaker than that of nonlabeled cells. Although it was rather difficult to analyze the morphology of Fluorogold-labeled neurons that exhibited PV immunoreactivity, some of them showed distinct apical dendrites and were considered pyramidal cells. The main target of PV-positive cortical afferents was the caudal striatum on the ipsilateral side. Next, we tested whether PV-positive corticostriatal projection neurons were GABAergic or not, because previous studies emphasized that PV was an important marker for cortical GABAergic neurons. Unexpectedly, we found that the majority of PV-positive corticostriatal projection neurons were glutamic acid decarboxylase (GAD)-negative, while some of them were GAD-positive. Finally, an anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) injection into the somatosensory cortex resulted in many PV-positive corticostriatal terminals that were vesicular glutamate transporter 1-positive, whereas some of the PV-positive PHA-L-labeled terminals were GAD-positive. Our results provide anatomical evidence for expression of PV in glutamatergic and GABAergic corticostriatal pathway in mice and suggest that a subset of cortical afferents may exert some inhibitory influence on striatal activity.

Animals↗
PubMed2005

Retrograde double-labeling study of common afferent projections to the dorsal raphe and the nuclear core of the locus coeruleus in the rat.

Common afferent projections to the dorsal raphe (DR) and locus coeruleus (LC) nuclei were analyzed in the rat by making paired injections of retrograde tracers, gold-conjugated and inactivated wheatgerm agglutinin-horseradish peroxidase (WGA-apo-HRP-gold) and Fluorogold (FG), into the DR and the nuclear core of the LC. Our results demonstrate that the largest number of double-labeled neurons was located at various preoptic regions including medial preoptic area, lateral preoptic nucleus, and ventrolateral preoptic nucleus. The majority of labeled cells were also observed at the lateral hypothalamus, where the number of labeled cells was comparable to that of neurons at the medial preoptic area or lateral preoptic nucleus. A few double-labeled cells were observed at various hypothalamic regions including anterior, medial tuberal, posterior, and arcuate nuclei, as well as mesencephalic areas including substantia nigra compacta and ventrolateral/lateral periaqueductal gray matter. Cells were also observed at prelimbic/infralimbic prefrontal cortices, diagonal band of Broca, bed nucleus of stria terminalis, and pontine/medullary regions including various raphe nuclei, Barrington's nucleus, gigantocellularis, paragigantocellularis, prepositus hypoglossi, subcoeruleus, and dorsomedial tegmental area. Although electrophysiological studies need to be performed, a large number of double-labeled neurons located at preoptic regions as well as lateral hypothalamus might have their major role in simultaneous control over these monoaminergic nuclei as a means of influencing various sleep and arousal states of the animal. Double-labeled cells at the other locations might be positioned to influence a variety of other functions such as analgesia, cognition, and stress responses.

Afferent Pathways↗
PubMed2005

Organization of hypocretin/orexin efferents to locus coeruleus and basal forebrain arousal-related structures.

Hypocretin/orexin neurons give rise to an extensive projection system, portions of which innervate multiple regions associated with the regulation of behavioral state. These regions include the locus coeruleus, medial septal area, medial preoptic area, and substantia innominata. Evidence indicates that hypocretin modulates behavioral state via actions within each of these terminal fields. To understand better the circuitry underlying hypocretin-dependent modulation of behavioral state, the present study characterized the degree to which there exists: 1) lateralization of hypocretin efferents to basal forebrain and brainstem arousal-related regions, 2) topographic organization of basal forebrain- and brainstem-projecting hypocretin neurons, and 3) collateralization of individual hypocretin neurons to these arousal-related terminal fields. These studies utilized combined immunohistochemical identification of hypocretin neurons with single or double retrograde tracing from the locus coeruleus, medial preoptic area, medial septal area, and substantia innominata. Results indicate that approximately 80% of hypocretin efferents to basal forebrain regions project ipsilaterally, whereas projections to the locus coeruleus are more bilateral (65%). There was a slight preference for basal forebrain-projecting hypocretin neurons to be distributed within the medial half of the hypocretin cell group. In contrast, hypocretin neurons projecting to the locus coeruleus were located primarily within the dorsal half of the hypocretin cell group. Finally, a large proportion of hypocretin neurons appear to project simultaneously to at least two of the examined terminal fields. These latter observations suggest coordinated actions of hypocretin across multiple arousal-related regions.

Animals↗
PubMed2005

Laterodorsal tegmental projections to identified cell populations in the rat ventral tegmental area.

Projections from the laterodorsal tegmentum (LDT) to the ventral tegmental area (VTA) contribute to the activity of dopamine (DA) and GABA cells and, hence, to the affective and cognitive functions of this region. LDT afferents arise from neurochemically diverse cell types and mediate multiple functional influences. However, the VTA cell populations that receive LDT afferents are unknown and were investigated here by anterograde and retrograde tract-tracing in combination with immunocytochemistry to distinguish DA and GABA cells. Approximately 50% of the LDT to VTA pathway formed asymmetric, presumably excitatory synapses that innervated DA and GABA cells in rough proportion to their representation within the VTA. This portion of the LDT innervation appeared to selectively target DA but not GABA mesoaccumbens neurons and provide a relatively nonselective input to both DA and GABA mesoprefrontal cells. The remaining LDT axons formed symmetric, presumably inhibitory synapses with a different pattern of cellular targets that included a preferential input to GABA neurons of both mesoaccumbens and mesoprefrontal populations and an apparently selective innervation of mesoprefrontal and not mesoaccumbens DA neurons. These data suggest that the LDT mediates a convergent excitatory and inhibitory influence on both mesoprefrontal DA and GABA cells but a divergent impact on mesoaccumbens neurons that is likely to excite DA cells and inhibit GABA neurons. Combined with our previous description of prefrontal cortical afferents, our data also indicate that mesoaccumbens DA neurons receive putative excitatory drive from the LDT, whereas mesoprefrontal DA cells receive convergent excitation from both cortical and brainstem sources.

Acetylcholine↗
PubMed2005

Thalamic innervation of the direct and indirect basal ganglia pathways in the rat: Ipsi- and contralateral projections.

The present study describes the thalamic innervation coming from the rat parafascicular nucleus (PF) onto striatal and subthalamic efferent neurons projecting either to the globus pallidus (GP) or to the substantia nigra pars reticulata (SNr) by using a protocol for multiple neuroanatomical tracing. Both striatofugal neurons targeting the ipsilateral SNr (direct pathway) as well as striatal efferent neurons projecting to the ipsilateral GP (indirect pathway) were located within the terminal fields of the thalamostriatal afferents. In the subthalamic nucleus (STN), both neurons projecting to ipsilateral GP as well as neurons projecting to ipsilateral SNr also appear to receive thalamic afferents. Although the projections linking the caudal intralaminar nuclei with the ipsilateral striatum and STN are far more prominent, we also noticed that thalamic axons could gain access to the contralateral STN. Furthermore, a small number of STN neurons were seen to project to both the contralateral GP and PF nuclei. These ipsi- and contralateral projections enable the caudal intralaminar nuclei to modulate the activity of both the direct and the indirect pathway.

Animals↗
PubMed2005

Vglut2 afferents to the medial prefrontal and primary somatosensory cortices: a combined retrograde tracing in situ hybridization study [corrected].

Glutamate transmission is critical for controlling cortical activity, but the specific contribution of the different isoforms of vesicular glutamate transporters in subcortical pathways to the neocortex is largely unknown. To determine the distribution and neocortical projections of vesicular glutamate transporter2 (Vglut2)-containing neurons, we used in situ hybridization and injections of the retrograde tracer Fluoro-Gold into the medial prefrontal and primary somatosensory cortices. The thalamus contains the majority of Vglut2 cells projecting to the neocortex (approximately 90% for the medial prefrontal cortex and 96% for the primary somatosensory cortex) followed by the hypothalamus and basal forebrain, the claustrum, and the brainstem. There are significantly more Vglut2 neurons projecting to the medial prefrontal cortex than to the primary somatosensory cortex. The medial prefrontal cortex also receives a higher percentage of Vglut2 projection from the hypothalamus than the primary somatosensory cortex. About 50% of thalamic Vglut2 projection to the medial prefrontal cortex and as much as 80% of the thalamic projection to primary somatosensory cortex originate in various relay thalamic nuclei. The remainder arise from different midline and intralaminar nuclei traditionally thought to provide nonspecific or diffuse projection to the cortex. The extrathalamic Vglut2 corticopetal projections, together with the thalamic intralaminar-midline Vglut2 corticopetal projections, may participate in diffuse activation of the neocortex.

Afferent Pathways↗
PubMed2005

Topography of pig retinal ganglion cells.

In the present work we analyzed the distribution of retinal ganglion cells (RGCs) in the pig retina. RGCs were retrogradely labeled in vivo by injecting Fluoro-Gold into the optic nerve. RGC density and the distribution of RGCs in terms of soma size were analyzed. Different regions of the porcine retina were identified following analysis of the distribution of RGCs in terms of cell density and soma size: in the central retina, we found a high-density horizontal RGC band lying dorsal to the optic disc. Moreover, in this region, a high proportion of RCGs with small soma size was observed. From the central to the more peripheral retina, we observed a decrease in RGC density, together with a greater presence of RGCs with larger somas. The results of this study should prove to be useful as a foundation for future studies with the porcine retina as a model in ophthalmic research. The study also highlights the necessity to label the RGC population specifically with retrograde tracers in order to quantify precisely alterations in the cell population associated with experimental treatments.

Animals↗
PubMed2005

TrkB expression and phospho-ERK activation by brain-derived neurotrophic factor in rat spinothalamic tract neurons.

Brain-derived neurotrophic factor (BDNF) is a neurotrophin implicated in the phenomena of synaptic plasticity in the adult. It is found in terminals of nociceptive primary afferents. Following a pain-related stimulus, it is released in the spinal cord, where it activates its high-affinity receptor TrkB, leading to the phosphorylation of the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase (ERK). A large body of evidence suggests that BDNF has a positive neuromodulatory effect on glutamate transmission in the spinal cord. However, none of these studies examined anatomically whether projection neurons known to be involved in transmission of nociceptive inputs express BDNF's receptor. Because the spinothalamic tract (STT) is a well-characterized pathway for its role in the transfer and integration of sensory and nociceptive informations, this study in rats aimed to 1) determine whether neurons of the STT pathway express the TrkB receptor, 2) establish the rostrocaudal and laminar distribution of STT-TrkB neurons in the whole spinal cord, and 3) test the potential functionality of TrkB expression in these cells by investigating the ability of BDNF to activate the MAP kinase ERK. Using tract tracing coupled to immunofluorescent labeling for TrkB, we observed that in all levels of the spinal cord most STT neurons were immunoreactive for TrkB. Furthermore, microinjections of BDNF into the spinal cord or release of endogenous BDNF by intraplantar injection of capsaicin activated ERK phosphorylation in TrkB-containing STT neurons. These data suggest an important role for BDNF in nociception as an activator of spinothalamic projection neurons.

Animals↗
PubMed2005

Morphologic evidence that neurokinin B modulates gonadotropin-releasing hormone secretion via neurokinin 3 receptors in the rat median eminence.

Recent studies suggest that arcuate neurokinin B (NKB) neurons play a role in the regulation of gonadotropin secretion, but there is little information on the relationship between these neurons and the hypothalamic reproductive axis. In the present study, dual-label fluorescent immunohistochemistry was used to visualize the relationship between gonadotropin-releasing hormone (GnRH) neurons and either proNKB or NK3 receptor (NK3R) immunoreactivity. Immunocytochemistry was also combined with i.p. injections of the fluorescent retrograde tracer aminostilbamidine to determine whether arcuate neuroendocrine neurons expressed either proNKB or NK3R. A dense interweaving and close apposition of GnRH and proNKB-immunoreactive (ir) fibers was observed within the rat median eminence, where GnRH axons expressed NK3R immunoreactivity. These data provide morphological evidence that NKB neurons could influence GnRH secretion via interaction with NK3R in the rat median eminence. Colocalization of GnRH and NK3R was also identified in fiber tracts converging within the organum vasculosum of the lamina terminalis. In contrast, only a small number (16%) of GnRH-ir somata exhibited NK3R staining. ProNKB and NK3R-ir somata were identified within the arcuate nucleus, but none of these neurons were labeled by aminostilbamidine. Thus, we found no evidence that arcuate NKB neurons project to the primary capillary plexus of the portal system. Arcuate neuroendocrine neurons, however, were surrounded and closely apposed by proNKB-ir puncta and fibers. These data suggest that NKB neurons could indirectly influence anterior pituitary function by inputs to arcuate neuroendocrine neurons, but through a receptor other than NK3R. Our results provide an anatomic framework for putative interactions between NKB neurons and the hypothalamic reproductive axis.

Animals↗
PubMed2005

Afferent connections of the amygdalopiriform transition area in the rat.

The amygdalopiriform transition area (APir) is often considered part of the lateral entorhinal cortex (Entl). However, in contrast to Entl, APir densely innervates the central extended amygdala (EAc) and does not project to the dentate gyrus. In order to gain a more comprehensive understanding of these territories, the afferent connections of APir were examined in the rat with retrograde (cholera toxin B subunit or FluoroGold) and anterograde tracers (Phaseolus vulgaris leucoagglutinin) and compared to those of the neighboring Entl. The results suggest that APir and Entl are interconnected and receive topographically organized hippocampal projections. Both are targeted by the olfactory bulb, the piriform, posterior agranular insular and perirhinal cortices, the ventral tegmental area, dorsal raphe nucleus, and locus coeruleus. Most importantly, the data reveal that APir and Entl also have specific inputs and should be viewed as separate anatomical entities. The APir receives robust projections from structures affiliated with the EAc, including the anterior basomedial and posterior basolateral amygdaloid nuclei, the gustatory thalamic region, parasubthalamic nucleus, and parabrachial area. The Entl is a major recipient for amygdaloid projections from the medial part of the lateral nucleus and the caudomedial part of the basolateral nucleus. Moreover, the medial septum, subicular complex, nucleus reuniens, supramammillary region, and nucleus incertus, which are associated with the hippocampal system, preferentially innervate the Entl. These data underscore that APir processes olfactory and gustatory information and is tightly linked to EAc operations, suggesting that it may play a role in reward mechanisms, particularly in hedonic aspects of feeding.

Afferent Pathways↗
PubMed2005

Afferents of the ventral tegmental area in the rat-anatomical substratum for integrative functions.

The ventral tegmental area (VTA) is critically important to an organism's capacity to detect rewards and novelty and to enlist appropriate behavioral responses. Although there has been substantial progress concerning information processing at the single cell and molecular levels in the VTA, our knowledge of its overall afferent connections is based principally on the benchmark description by Phillipson ([1979] J. Comp. Neurol. 187:117-144). Given that, since then, the sensitivity of tracing methods and knowledge about the organization of brain structures have increased considerably, we undertook to reevaluate the VTA afferents of the rat. The retrograde tracer Fluoro-Gold was injected into different parts of the VTA, and labeled neurons were visualized by immunocytochemistry. Retrogradely labeled neurons were not confined to nuclei but rather constituted an elongated formation stretching from the prefrontal cortex rostrally to the medulla oblongata caudally. In the case of descending afferents, this formation was centered on the medial forebrain bundle and the fasciculus retroflexus. The input to the VTA in general was bilateral, with a smaller descending and comparable ascending projection from the contralateral side. Injections of the anterograde tracers Phaseolus vulgaris-leucoagglutinin or biotinylated dextran amine into selected forebrain structures revealed a surprisingly sparse terminal arborization in the VTA. Furthermore, structures projecting to the VTA innervate other brain areas with similar or greater robustness, which in turn also provide a strong input to the VTA, indicating an anatomical network. Given the importance of the VTA in basic behaviors, this organization might provide a basis for an extraordinary level of afferent integration.

Afferent Pathways↗
PubMed2006

Distinct subpopulations of cyclic guanosine monophosphate (cGMP) and neuronal nitric oxide synthase (nNOS) containing sympathetic preganglionic neurons in spontaneously hypertensive and Wistar-Kyoto rats.

The sympathetic preganglionic neurons (SPN) of the intermediolateral cell column (IML) play a critical role in the maintenance of vascular tone. We undertook a comparative neuroanatomical analysis of neuronal nitric oxide synthase (nNOS) expression in the SPN of the mature normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rat (SHR). The anatomical relationship between nNOS and the NO signaling molecule cyclic guanosine monophosphate (cGMP) was also determined. All animals were male, age > 6 months. Fluorogold (FG) retrograde labeling of SPN (detected with immunohistochemistry) was combined with NADPH-diaphorase histochemistry for NOS in the thoracic spinal cord (T1-11, n = 5 WKY, 5 SHR). There was no difference in the total number of FG-labeled SPN (WKY 6,542 +/- 828, SHR 6,091 +/- 820), but the proportion of FG-labeled cells expressing NOS was significantly less in the SHR (WKY 64.4 +/- 5.1 vs. SHR 55.6 +/- 2.1, P < 0.05). Fluorescence immunohistochemistry for nNOS/cGMP (n = 4 WKY, 4 SHR) was also performed. Confocal microscopy revealed that all nNOS-positive SPN contain cGMP and confirmed a strain-specific anatomical arrangement of SPN cell clusters. A novel subpopulation of cGMP-only cells were also identified. Double labeling for cGMP and choline acetyltransferase (n = 3 WKY, 3 SHR), confirmed these cells as SPN in both WKY and SHR. These results suggest that cGMP is a key signaling molecule in SPN, and that a reduced number of NOS neurons in the SHR may play a role in the increase in sympathetic tone associated with hypertension in these animals.

Acetylcholine↗
PubMed2006

Phototoxic-induced photoreceptor degeneration causes retinal ganglion cell degeneration in pigmented rats.

Human retinitis pigmentosa results eventually in retinal ganglion cell (RGC) death, but how this occurs remains obscure. We have previously documented that in pigmented dystrophic Royal College of Surgeons (RCS) rats, photoreceptor degeneration is followed by retinal pigment epithelial (RPE) migration, formation of RPE-vascular complexes, and vascular displacement that causes RGC axonal compression and death. To investigate if phototoxic-induced photoreceptor degeneration is capable of causing similar pathologic events, we dilated the left pupil of pigmented nondystrophic RCS and Lister-Hooded rats and exposed them to light (3000 lux) for 72 hours. After various survival periods ranging between 0 hours and 21 months, the retinas were processed as whole mounts or in cross-sections. Two separate retinal degenerative events that may relate to differential light exposure across the retina were observed: an early arciform area of degeneration in the superotemporal retina and a delayed degeneration in the central and ventral retina. Although degeneration in the arciform area was always more severe and developed earlier (sensitive region), both of them showed quite comparable pathologic events to those described for dystrophic RCS rats. RGC axonal compression was seen as soon as 21 days after light exposure and RGC loss was seen 9 months after light exposure, mainly in the superotemporal retina, but also in the ventral retina. The results show that RGC loss in induced photoreceptor degeneration results from a similar series of events to those occurring as a consequence of inherited degeneration and therefore is not uniquely a property of inherited photoreceptor degeneration.

Animals↗
PubMed2006

Topography of cortical projections to the dorsolateral neostriatum in rats: multiple overlapping sensorimotor pathways.

In rodents, the whisker representation in primary somatosensory (SI) cortex projects to the dorsolateral neostriatum, but the location of these projections has never been characterized with respect to layer IV barrels and their intervening septa. To address this issue, we injected a retrograde tracer into the dorsolateral neostriatum and then reconstructed the location of the labeled corticostriatal neurons with respect to the cytochrome oxidase (CO)-labeled barrels in SI. When the tracer was restricted to a small focal site in the neostriatum, the retrogradely labeled neurons formed elongated strips that were parallel to the curvilinear orientation of layer IV barrel rows. After larger tracer injections, labeled neurons were distributed uniformly across layer V and were aligned with both the barrel and septal compartments. Labeled projections from the contralateral SI barrel cortex, however, were much fewer in number and were disproportionately associated with the septal compartments. A comparison of the labeling patterns in the ipsilateral and contralateral hemispheres revealed symmetric, mirror-image distributions that extended across primary motor cortex (MI) and multiple somatosensory cortical regions, including the secondary somatosensory (SII) cortex, the parietal ventral (PV) and parietal rhinal (PR) areas, and the posteromedial (PM) region. Examination of the thalamus revealed labeled neurons in the intralaminar nuclei, in the medial part of the posterior nucleus (POm), and in the ventrobasal complex. These results indicate that the dorsolateral neostriatum integrates sensorimotor information from multiple sensorimotor representations in the thalamus and cortex.

Animals↗
PubMed2006

Differential origin of projections from SI barrel cortex to the whisker representations in SII and MI.

We have previously shown that projections from SI barrel cortex to the MI whisker representation originate primarily from columns of neurons that are aligned with the layer IV septa. SI barrel cortex also projects to SII cortex, but the origin of these projections has not been characterized with respect to the barrel and septal compartments. To address this issue, we injected retrograde tracers into the SII whisker representation and then reconstructed the location of the labeled neurons in SI with respect to the layer IV barrels. In some animals, two different tracers were injected into the whisker representations of SII and MI to detect double-labeled neurons that would indicate that some SI neurons project to both of these cortical areas. We found that the projections to SII cortex originate from sites that are uniformly distributed throughout the extragranular layers of barrel cortex. In cases in which different tracers were injected in SII and MI, double-labeled neurons appeared above and below the layer IV septal compartment and at sites aligned with the boundaries of the layer IV barrels. To the extent that the columns of neurons aligned with the barrel and septal compartments represent functionally distinct circuits, these results indicate that SII receives information from both circuits, whereas MI receives inputs primarily from the septal circuits.

Amidines↗
PubMed2006

Selective distribution and function of primary afferent nociceptive inputs from deep muscle tissue to the brainstem trigeminal transition zone.

Orofacial injury activates two distinct regions in the spinal trigeminal complex, the subnuclei interpolaris/caudalis (Vi/Vc) transition zone and the laminated Vc, or medullary dorsal horn (MDH). Studies suggest that the Vi/Vc transition zone plays an important role in processing orofacial deep input. To test this hypothesis, we employed a double-tracing strategy to compare central projections of primary afferent neurons that innervate the masseter muscle and the overlying skin. Different tracers were injected either centrally (Fluoro-Gold: ventral Vi/Vc, or MDH) or peripherally (wheat germ agglutinin-conjugated horseradish peroxidase or cholera toxin B: masseter or overlying skin) in the same rat. Trigeminal ganglion tissue sections were processed for single or double immunohistochemistry. The double labeling of ganglion neurons indicates their site of peripheral and central innervations. A population of small to medium-sized neurons was doubly labeled after injections of the tracers into the masseter-Vi/Vc, masseter-MDH, or the skin-MDH. However, only a few double-labeled neurons were occasionally observed after injections of the tracers into the skin-Vi/Vc. Injection of an N-methyl-D-aspartate receptor antagonist, AP-5, into the Vi/Vc and MDH attenuated masseter inflammatory hyperalgesia. In contrast, hyperalgesia after inflammation of the skin overlying the masseter was attenuated by injection of AP-5 into the MDH but not Vi/Vc. These results indicate that while both masseter and cutaneous inputs project to the MDH, masseter afferents provide an additional input to the Vi/Vc. These findings provide further evidence to support a role of the trigeminal transition zone in response to orofacial deep injury.

Afferent Pathways↗
PubMed2006

Vesicular glutamate transporter 3 immunoreactivity is present in cholinergic basal forebrain neurons projecting to the basolateral amygdala in rat.

The basal forebrain (BF) plays a role in behavioral and cortical arousal, attention, learning, and memory. It has been suggested that cholinergic BF neurons co-release glutamate, and some cholinergic BF neurons have been reported to contain vesicular glutamate transporter 3 (VGLUT3). We examined the distribution and projections of BF cholinergic neurons containing VGLUT3, by using dual-label immunofluorescence for choline acetyltransferase (ChAT) and VGLUT3, in situ hybridization, and retrograde tracing. Neurons immunoreactive (+) or containing mRNAs for both ChAT and VGLUT3 were mainly localized to the ventral pallidum and more caudal BF regions; the co-immunoreactive neurons represented 31% of cholinergic neurons in the ventral pallidum and 5-9% more caudally. Examination of cholinergic axon terminals in known target areas of BF projections indicated that the basolateral amygdaloid nucleus contained numerous terminals co-immunoreactive for ChAT and VGLUT3, whereas sampled areas of the olfactory bulb, neocortex, hippocampus, reticular thalamic nucleus, and interpeduncular nucleus were devoid of double-labeled terminals. The basolateral amygdala is innervated by cholinergic BF neurons lacking low-affinity p75 nerve growth factor receptors; many ChAT+VGLUT3+ BF neurons were immunonegative to this receptor. Twenty-five to 79% of ChAT+VGLUT3+ neurons in different BF regions were retrogradely labeled from the basolateral amygdala, up to 52% (ventral pallidum) of the retrogradely labeled ChAT+ neurons were VGLUT3+, and the largest number of amygdala-projecting ChAT+VGluT3+ neurons was found in the ventral pallidum. These findings indicate that BF cholinergic neurons containing VGLUT3 project to the basolateral amygdala and suggest that these neurons might have the capacity to release both acetylcholine and glutamate.

Amygdala↗