Relationships between neuronal birthdates and tonotopic positions in the mouse cochlear nucleus

Tonotopy is a key anatomical feature of the vertebrate auditory system, but little is known about the mechanisms underlying its development. Since date of birth of a neuron correlates with tonotopic position in the cochlea, we investigated if it also correlates with tonotopic position in the cochlear nucleus (CN). In the cochlea, spiral ganglion neurons are organized in a basal to apical progression along the length of the cochlea based on birthdates, with neurons in the base (responding to high-frequency sounds) born early around mouse embryonic day (E) 9.5–10.5, and those in the apex (responding to low-frequency sounds) born late around E12.5‑13.5. Using a low-dose thymidine analog incorporation assay, we examine whether CN neurons are arranged in a spatial gradient according to their birthdates. Most CN neurons are born between E10.5 ānd E13.5, with a peak at E12.5. A second wave of neuron birth was observed in the dorsal cochlear nucleus (DCN) beginning on E14.5 and lasts until E18.5. Large excitatory neurons were born in the first wave, and small local circuit neurons were born in the second. No spatial gradient of cell birth was observed in the DCN. In contrast, neurons in the anteroventral cochlear nucleus (AVCN) were found to be arranged in a dorsal to ventral progression according to their birthdates, which are aligned with the tonotopic axis. Most of these AVCN neurons are endbulb-innervated bushy cells. The correlation between birthdate and tonotopic position suggests testable mechanisms for specification of tonotopic position.     

GABAA and GABAB receptor subunit localization on neurochemically identified neurons of the human subthalamic nucleus

The subthalamic nucleus (STN) is a critical excitatory signaling center within the basal ganglia circuitry. The activity of subthalamic neurons is tightly controlled by upstream inhibitory signaling centers in the basal ganglia. In this study, we used immunohistochemical techniques to firstly, visualize and quantify the STN neurochemical organization based on neuronal markers including parvalbumin (PV), calretinin (CR), SMI‐32, and GAD_65/67. Secondly, we characterized the detailed regional, cellular and subcellular expression of GABA_A (α₁, α₂, α₃, β_2/3, and γ₂) and GABA_B (R1 and R2) receptor subunits within the normal human STN. Overall, we found seven neurochemically distinct populations of principal neurons in the human STN. The three main populations detected were: (a) triple‐labeled PV⁺/CR⁺/SMI32⁺; (b) double‐labeled PV⁺/CR⁺; and (c) single‐labeled CR⁺ neurons. Subthalamic principal neurons were found to express GABA_A receptor subunits α₁, α₃, β_2/3, γ₂, and GABA_B receptor subunits R1 and R2. However, no expression of GABA_A receptor α₂ subunit was detected. We also found a trend of increasing regional staining intensity for all positive GABA_A receptor subunits from the dorsolateral pole to ventromedial extremities. The GAD⁺ interneurons showed relatively low expression of GABA_A receptor subunits. These results provide the morphological basis of GABAergic transmission within the normal human subthalamic nucleus and evidence of GABA innervation through both GABA_A and GABA_B receptors on subthalamic principal neurons.     

Astrocytic glutamate transport regulates a Drosophila CNS synapse that lacks astrocyte ensheathment

Anatomical, molecular, and physiological interactions between astrocytes and neuronal synapses regulate information processing in the brain. The fruit fly Drosophila melanogaster has become a valuable experimental system for genetic manipulation of the nervous system and has enormous potential for elucidating mechanisms that mediate neuron–glia interactions. Here, we show the first electrophysiological recordings from Drosophila astrocytes and characterize their spatial and physiological relationship with particular synapses. Astrocyte intrinsic properties were found to be strongly analogous to those of vertebrate astrocytes, including a passive current‐voltage relationship, low membrane resistance, high capacitance, and dye‐coupling to local astrocytes. Responses to optogenetic stimulation of glutamatergic premotor neurons were correlated directly with anatomy using serial electron microscopy reconstructions of homologous identified neurons and surrounding astrocytic processes. Robust bidirectional communication was present: neuronal activation triggered astrocytic glutamate transport via excitatory amino acid transporter 1 (Eaat1), and blocking Eaat1 extended glutamatergic interneuron‐evoked inhibitory postsynaptic currents in motor neurons. The neuronal synapses were always located within 1 μm of an astrocytic process, but none were ensheathed by those processes. Thus, fly astrocytes can modulate fast synaptic transmission via neurotransmitter transport within these anatomical parameters. J. Comp. Neurol. 524:1979–1998, 2016. © 2016 Wiley Periodicals, Inc.     

Spatial patterning of excitatory and inhibitory neuropil territories during spinal circuit development

To generate rhythmic motor behaviors, both single neurons and neural circuits require a balance between excitatory inputs that trigger action potentials and inhibitory inputs that promote a stable resting potential (E/I balance). Previous studies have focused on individual neurons and have shown that, over a short spatial scale, excitatory and inhibitory (E/I) synapses tend to form structured territories with inhibitory inputs enriched on cell bodies and proximal dendrites and excitatory inputs on distal dendrites. However, systems‐level E/I patterns, at spatial scales larger than single neurons, are largely uncharted. We used immunostaining for PSD‐95 and gephyrin postsynaptic scaffolding proteins as proxies for excitatory and inhibitory synapses, respectively, to quantify the numbers and map the distributions of E/I synapses in zebrafish spinal cord at both an embryonic stage and a larval stage. At the embryonic stage, we found that PSD‐95 puncta outnumber gephyrin puncta, with the number of gephyrin puncta increasing to match that of PSD‐95 puncta at the larval stage. At both stages, PSD‐95 puncta are enriched in the most lateral neuropil corresponding to distal dendrites while gephyrin puncta are enriched on neuronal somata and in the medial neuropil. Significantly, similar to synaptic puncta, neuronal processes also exhibit medial‐lateral territories at both developmental stages with enrichment of glutamatergic (excitatory) processes laterally and glycinergic (inhibitory) processes medially. This establishment of neuropil excitatory‐inhibitory structure largely precedes dendritic arborization of primary motor neurons, suggesting that the structured neuropil could provide a framework for the development of E/I balance at the cellular level. J. Comp. Neurol. 525:1649–1667, 2017. © 2016 Wiley Periodicals, Inc.     

Neurochemistry of neurons in the ventrolateral medulla activated by hypotension: Are the same neurons activated by glucoprivation?

Previous studies have demonstrated that a range of stimuli activate neurons, including catecholaminergic neurons, in the ventrolateral medulla. Not all catecholaminergic neurons are activated and other neurochemical content is largely unknown hence whether stimulus specific populations exist is unclear. Here we determine the neurochemistry (using in situ hybridization) of catecholaminergic and noncatecholaminergic neurons which express c‐Fos immunoreactivity throughout the rostrocaudal extent of the ventrolateral medulla, in Sprague Dawley rats treated with hydralazine or saline. Distinct neuronal populations containing PPCART, PPPACAP, and PPNPY mRNAs, which were largely catecholaminergic, were activated by hydralazine but not saline. Both catecholaminergic and noncatecholaminergic neurons containing preprotachykinin and prepro‐enkephalin (PPE) mRNAs were also activated, with the noncatecholaminergic population located in the rostral C1 region. Few GlyT2 neurons were activated. A subset of these data was then used to compare the neuronal populations activated by 2‐deoxyglucose evoked glucoprivation (Brain Structure and Function (2015) 220:117). Hydralazine activated more neurons than 2‐deoxyglucose but similar numbers of catecholaminergic neurons. Commonly activated populations expressing PPNPY and PPE mRNAs were defined. These likely include PPNPY expressing catecholaminergic neurons projecting to vasopressinergic and corticotrophin releasing factor neurons in the paraventricular nucleus, which when activated result in elevated plasma vasopressin and corticosterone. Stimulus specific neurons included noncatecholaminergic neurons and a few PPE positive catecholaminergic neuron but neurochemical codes were largely unidentified. Reasons for the lack of identification of stimulus specific neurons, readily detectable using electrophysiology in anaesthetized preparations and for which neural circuits can be defined, are discussed.     

Highly segregated localization of the functionally related vps10p receptors sortilin and SorCS2 during neurodevelopment

Nervous system development is a precisely orchestrated series of events requiring a multitude of intrinsic and extrinsic cues. Sortilin and SorCS2 are members of the Vps10p receptor family with complementary influence on some of these cues including the neurotrophins (NTs). However, the developmental time points where sortilin and SorCS2 exert their activities in conjunction or independently still remain unclear. In this study we present the characterization of the spatiotemporal expression pattern of sortilin and SorCS2 in the developing murine nervous system. Sortilin is highly expressed in the fetal nervous system with expression localized to distinct cell populations. Expression was high in neurons of the cortical plate and developing allocortex, as well as subpallial structures. Furthermore, the neuroepithelium lining the ventricles and the choroid plexus showed high expression of sortilin, together with the developing retina, spinal ganglia, and sympathetic ganglia. In contrast, SorCS2 was confined in a marked degree to the thalamus and, at E13.5, the floor plate from midbrain rostrally to spinal cord caudally. SorCS2 was also found in the ventricular zones of the ventral hippocampus and nucleus accumbens areas, in the meninges and in Schwann cells. Hence, sortilin and SorCS2 are extensively present in several distinct anatomical areas in the developing nervous system and are rarely co‐expressed. Possible functions of sortilin and SorCS2 pertain to NT signaling, axon guidance and beyond. The present data will form the basis for hypotheses and study designs for unravelling the functions of sortilin and SorCS2 during the establishment of neuronal structures and connections.     

Characterization of the axon initial segment of mice substantia nigra dopaminergic neurons

The axon initial segment (AIS) is the site of initiation of action potentials and influences action potential waveform, firing pattern, and rate. In view of the fundamental aspects of motor function and behavior that depend on the firing of substantia nigra pars compacta (SNc) dopaminergic neurons, we identified and characterized their AIS in the mouse. Immunostaining for tyrosine hydroxylase (TH), sodium channels (Na_v) and ankyrin‐G (Ank‐G) was used to visualize the AIS of dopaminergic neurons. Reconstructions of sampled AIS of dopaminergic neurons revealed variable lengths (12–60 μm) and diameters (0.2–0.8 μm), and an average of 50% reduction in diameter between their widest and thinnest parts. Ultrastructural analysis revealed submembranous localization of Ank‐G at nodes of Ranvier and AIS. Serial ultrathin section analysis and 3D reconstructions revealed that Ank‐G colocalized with TH only at the AIS. Few cases of synaptic innervation of the AIS of dopaminergic neurons were observed. mRNA in situ hybridization of brain‐specific Na_v subunits revealed the expression of Na_v1.2 by most SNc neurons and a small proportion expressing Na_v1.6. The presence of sodium channels, along with the submembranous location of Ank‐G is consistent with the role of AIS in action potential generation. Differences in the size of the AIS likely underlie differences in firing pattern, while the tapering diameter of AIS may define a trigger zone for action potentials. Finally, the conspicuous expression of Na_v1.2 by the majority of dopaminergic neurons may explain their high threshold for firing and their low discharge rate.     

The nucleus pretectalis principalis: A pretectal structure hidden in the mammalian thalamus

A defining feature of the amniote tecto-fugal visual pathway is a massive bilateral projection to the thalamus originating from a distinct neuronal population, tectal ganglion cells (TGCs), of the optic tectum/superior colliculus (TeO/SC). In sauropsids, the thalamic target of the tecto-fugal pathway is the nucleus rotundus thalami (Rt). TGCs axons collateralize en route to Rt to target the nucleus pretectalis principalis (PT), which in turn gives rise to bilateral projection to the TeO. In rodents, the thalamic target of these TGCs afferents is the caudal division of the pulvinar complex (PulC). No pretectal structures in receipt of TGC collaterals have been described in this group. However, Baldwin et al. (Journal of Comparative Neurology, 2011;519(6):1071–1094) reported in the squirrel a feedback projection from the PulC to the SC. Pulvino-tectal (Pul-T) cells lie at the caudal pole of the PulC, intermingled with the axonal terminals of TGCs. Here, by performing a combination of neuronal tracing, immunohistochemistry, immunofluorescence, and in situ hybridization, we characterized the pattern of projections, neurochemical profile, and genoarchitecture of Pul-T cells in the diurnal Chilean rodent Octodon degus. We found that Pul-T neurons exhibit pretectal, but not thalamic, genoarchitectonical markers, as well as hodological and neurochemical properties that match specifically those of the avian nucleus PT. Thus, we propose that Pul-T cells constitute a pretectal cell population hidden within the dorsal thalamus of mammals. Our results solve the oddity entailed by the apparent existence of a noncanonic descending sensory thalamic projection and further stress the conservative character of the tectofugal pathway.     

Organization of alpha‐transducin immunoreactive system in the brain and retina of larval and young adult Sea Lamprey (Petromyzon marinus), and their relationship with other neural systems

We employed an anti‐transducin antibody (Gαt‐S), in combination with other markers, to characterize the Gαt‐S‐immunoreactive (ir) system in the CNS of the sea lamprey, Petromyzon marinus. Gαt‐S immunoreactivity was observed in some neuronal populations and numerous fibers distributed throughout the brain. Double Gαt‐S‐ and opsin‐ir neurons (putative photoreceptors) are distributed in the hypothalamus (postoptic commissure nucleus, dorsal and ventral hypothalamus) and caudal diencephalon, confirming results of García‐Fernández et al. (Cell and Tissue Research, 288, 267–278, 1997). Singly Gαt‐S‐ir cells were observed in the midbrain and hindbrain, increasing the known populations. Our results reveal for the first time in vertebrates the extensive innervation of many brain regions and the spinal cord by Gαt‐S‐ir fibers. The Gαt‐S innervation of the habenula is very selective, fibers densely innervating the lamprey homologue of the mammalian medial nucleus (Stephenson‐Jones et al., Proceedings of the National Academy of Sciences of the United States of America, 109, E164–E173, 2012), but not the lateral nucleus homologue. The lamprey neurohypophysis was not innervated by Gαt‐S‐ir fibers. We also analyzed by double immunofluorescence the relation of this system with other systems. A dopaminergic marker (TH), serotonin (5‐HT) or GABA do not co‐localize with Gαt‐S‐ir neurons although codistribution of fibers was observed. Codistribution of Gαt‐S‐ir fibers and isolectin‐labeled extrabulbar primary olfactory fibers was observed in the striatum and hypothalamus. Neurobiotin retrograde transport from the spinal cord combined with immunofluorescence revealed spinal‐projecting Gαt‐S‐ir reticular neurons in the caudal hindbrain. Present results in an ancient vertebrate reveal for the first time a collection of brain targets of Gαt‐S‐ir neurons, suggesting they might mediate non‐visual modulation by light in many systems.     

Interstitial branch formation within the red nucleus by deep cerebellar nuclei‐derived commissural axons during target recognition

Target recognition by developing axons is one of the fundamental steps for establishing the proper pattern of neuronal connectivity during development. However, knowledge of the mechanisms that underlie this critical event is still limited. In this study, to examine how commissural axons in vertebrates recognize their targets after crossing the midline, we analyzed in detail the behavior of postcrossing commissural axons derived from the deep cerebellar nuclei (DCN) in the developing mouse cerebellum. For this, we employed a cell‐type‐specific genetic labeling approach to selectively visualize DCN axons during the time when these axons project to the red nucleus (RN), one of the well‐characterized targets of DCN axons. We found that, when DCN axons initially entered the RN at its caudal end, these axons continued to grow rostrally through the RN without showing noticeable morphological signs of axon branching. Interestingly, after a delay, DCN axons started forming interstitial branches from the portion of the axon shaft selectively within the RN. Because commissural axons acquire responsiveness to several guidance cues when they cross the midline, we further addressed whether midline crossing is a prerequisite for subsequent targeting by using a Robo3 knockdown strategy. We found that DCN axons were still capable of forming interstitial branches within the RN even in the absence of midline crossing. These results therefore suggest that the mechanism of RN recognition by DCN axons involves a delayed interstitial branching, and that these axons possess an intrinsic ability to respond to the target‐derived cues irrespective of midline crossing. J. Comp. Neurol. 524:999–1014, 2016. © 2015 Wiley Periodicals, Inc.     

Convergence of lemniscal and local excitatory inputs on large GABAergic tectothalamic neurons

Large GABAergic (LG) neurons form a distinct cell type in the inferior colliculus (IC), identified by the presence of dense VGLUT2‐containing axosomatic terminals. Although some of the axosomatic terminals originate from local and commissural IC neurons, it has been unclear whether LG neurons also receive axosomatic inputs from the lower auditory brainstem nuclei, i.e., cochlear nuclei (CN), superior olivary complex (SOC), and nuclei of the lateral lemniscus (NLL). In this study we injected recombinant viral tracers that force infected cells to express GFP in a Golgi‐like manner into the lower auditory brainstem nuclei to determine whether these nuclei directly innervate LG cell somata. Labeled axons from CN, SOC, and NLL terminated as excitatory axosomatic endings, identified by colabeling of GFP and VGLUT2, on single LG neurons in the IC. Each excitatory axon made only a few axosomatic contacts on each LG neuron. Inputs to a single LG cell are unlikely to be from a single brainstem nucleus, since lesions of individual nuclei failed to eliminate most VGLUT2‐positive terminals on the LG neurons. The estimated number of inputs on a single LG cell body was almost proportional to the surface area of the cell body. Double injections of different viruses into IC and a brainstem nucleus showed that LG neurons received inputs from both. These results demonstrated that both ascending and intrinsic sources converge on the LG somata to control inhibitory tectothalamic projections. J. Comp. Neurol. 523:2277–2296, 2015. © 2015 Wiley Periodicals, Inc.     

Cholinergic profiles in the Goettingen miniature pig (Sus scrofa domesticus) brain

Central cholinergic structures within the brain of the even‐toed hoofed Goettingen miniature domestic pig (Sus scrofa domesticus) were evaluated by immunohistochemical visualization of choline acetyltransferase (ChAT) and the low‐affinity neurotrophin receptor, p75^NTR. ChAT‐immunoreactive (‐ir) perikarya were seen in the olfactory tubercle, striatum, medial septal nucleus, vertical and horizontal limbs of the diagonal band of Broca, and the nucleus basalis of Meynert, medial habenular nucleus, zona incerta, neurosecretory arcuate nucleus, cranial motor nuclei III and IV, Edinger‐Westphal nucleus, parabigeminal nucleus, pedunculopontine nucleus, and laterodorsal tegmental nucleus. Cholinergic ChAT‐ir neurons were also found within transitional cortical areas (insular, cingulate, and piriform cortices) and hippocampus proper. ChAT‐ir fibers were seen throughout the dentate gyrus and hippocampus, in the mediodorsal, laterodorsal, anteroventral, and parateanial thalamic nuclei, the fasciculus retroflexus of Meynert, basolateral and basomedial amygdaloid nuclei, anterior pretectal and interpeduncular nuclei, as well as select laminae of the superior colliculus. Double immunofluorescence demonstrated that virtually all ChAT‐ir basal forebrain neurons were also p75^NTR‐positive. The present findings indicate that the central cholinergic system in the miniature pig is similar to other mammalian species. Therefore, the miniature pig may be an appropriate animal model for preclinical studies of neurodegenerative diseases where the cholinergic system is compromised. J. Comp. Neurol. 525:553–573, 2017. © 2016 Wiley Periodicals, Inc.     

Reelin receptors ApoER2 and VLDLR are expressed in distinct spatiotemporal patterns in developing mouse cerebral cortex

In mammalian developing brain, neuronal migration is regulated by a variety of signaling cascades, including Reelin signaling. Reelin is a glycoprotein that is mainly secreted by Cajal–Retzius neurons in the marginal zone, playing essential roles in the formation of the layered neocortex via its receptors, apolipoprotein E receptor 2 (ApoER2) and very low density lipoprotein receptor (VLDLR). However, the precise mechanisms by which Reelin signaling controls the neuronal migration process remain unclear. To gain insight into how Reelin signaling controls individual migrating neurons, we generated monoclonal antibodies against ApoER2 and VLDLR and examined the localization of Reelin receptors in the developing mouse cerebral cortex. Immunohistochemical analyses revealed that VLDLR is localized to the distal portion of leading processes in the marginal zone (MZ), whereas ApoER2 is mainly localized to neuronal processes and the cell membranes of multipolar cells in the multipolar cell accumulation zone (MAZ). These different expression patterns may contribute to the distinct actions of Reelin on migrating neurons during both the early and late migratory stages in the developing cerebral cortex. J. Comp. Neurol. 523:463–478, 2015. © 2014 Wiley Periodicals, Inc.     

Synaptic localization of the SUMOylation‐regulating protease SENP5 in the adult mouse brain

Covalent conjugation of small ubiquitin‐like modifiers (SUMOs) or SUMOylation is a reversible post‐translational modification that regulates the stability and function of target proteins. SUMOs are removed from substrate proteins by sentrin/SUMO‐specific proteases (SENPs). Numerous studies have implicated SUMOylation in various physiological and pathological processes in neurons. To understand the functional roles of SUMOylation, it is necessary to determine the distribution of enzymes regulating SUMO conjugation and deconjugation; yet, the localization of SENPs has not been described in detail in intact brain tissue. Here, we report the distribution and subcellular localization of SENP3 and 5 in the adult murine brain. Immunohistochemical analyses revealed the ubiquitous distribution of both SENPs across different brain regions. Within individual cells, SENP3 was confined to the nucleus, consistent with the conventional view that SENPs regulate nuclear events. In contrast, SENP5 was detected in the neuropil but not in cell bodies. Moreover, strong SENP5 immunoreactivity was observed in regions with high numbers of synapses such as the cerebellar glomeruli, suggesting that SENP5 localizes to pre‐ and/or postsynaptic structures. We performed double immunolabeling in cultured neurons and found that SENP5 co‐localized with pre‐ and post‐synaptic markers, as well as a mitochondrial marker. Immunoelectron microscopy confirmed this finding and revealed that SENP5 was localized to presynaptic terminals, postsynaptic spines, and mitochondria in axon terminals. These findings advance the current understanding of the functional roles of SUMOylation in neurons, especially in synaptic regulation, and have implications for future therapeutic strategies in neurodegenerative disorders mediated by mitochondrial dysfunction.     

Monosynaptic retrograde tracing of neurons expressing the G‐protein coupled receptor Gpr151 in the mouse brain

GPR151 is a G‐protein coupled receptor for which the endogenous ligand remains unknown. In the nervous system of vertebrates, its expression is enriched in specific diencephalic structures, where the highest levels are observed in the habenular area. The habenula has been implicated in a range of different functions including behavioral flexibility, decision making, inhibitory control, and pain processing, which makes it a promising target for treating psychiatric and neurological disease. This study aimed to further characterize neurons expressing the Gpr151 gene, by tracing the afferent connectivity of this diencephalic cell population. Using pseudotyped rabies virus in a transgenic Gpr151‐Cre mouse line, monosynaptic afferents of habenular and thalamic Gpr151‐expressing neuronal populations could be visualized. The habenular and thalamic Gpr151 systems displayed both shared and distinct connectivity patterns. The habenular neurons primarily received input from basal forebrain structures, the bed nucleus of stria terminalis, the lateral preoptic area, the entopeduncular nucleus, and the lateral hypothalamic area. The Gpr151‐expressing neurons in the paraventricular nucleus of the thalamus was primarily contacted by medial hypothalamic areas as well as the zona incerta and projected to specific forebrain areas such as the prelimbic cortex and the accumbens nucleus. Gpr151 mRNA was also detected at low levels in the lateral posterior thalamic nucleus which received input from areas associated with visual processing, including the superior colliculus, zona incerta, and the visual and retrosplenial cortices. Knowledge about the connectivity of Gpr151‐expressing neurons will facilitate the interpretation of future functional studies of this receptor.     

The distribution,number, and certain neurochemical identities of infracortical white matter neurons in a lar gibbon (Hylobates lar) brain

We examined the number, distribution, and immunoreactivity of the infracortical white matter neuronal population, also termed white matter interstitial cells (WMICs), in the brain of a lesser ape, the lar gibbon. Staining for neuronal nuclear marker (NeuN) revealed WMICs throughout the infracortical white matter, these cells being most numerous and dense close to cortical layer VI, decreasing significantly in density with depth in the white matter. Stereological analysis of NeuN-immunopositive cells revealed a global estimate of ~67.5 million WMICs within the infracortical white matter of the gibbon brain, indicating that the WMICs are a numerically significant population, ~2.5% of the total cortical gray matter neurons that would be estimated for a primate brain the mass of that of the lar gibbon. Immunostaining revealed subpopulations of WMICs containing neuronal nitric oxide synthase (nNOS, ~7 million in number, with both small and large soma volumes), calretinin (~8.6 million in number, all of similar soma volume), very few WMICs containing parvalbumin, and no calbindin-immunopositive neurons. These nNOS, calretinin, and parvalbumin immunopositive WMICs, presumably all inhibitory neurons, represent ~23.1% of the total WMIC population. As the white matter is affected in many cognitive conditions, such as schizophrenia, autism and also in neurodegenerative diseases, understanding these neurons across species is important for the translation of findings of neural dysfunction in animal models to humans. Furthermore, studies of WMICs in species such as apes provide a crucial phylogenetic context for understanding the evolution of these cell types in the human brain.     

Quantitative analysis of axon bouton distribution of subthalamic nucleus neurons in the rat by single neuron visualization with a viral vector

The subthalamic nucleus (STN) of the basal ganglia plays a key role in motor control, and STN efferents are known to mainly target the external segment of the globus pallidus (GPe), entopeduncular nucleus (Ep), and substantia nigra (SN) with some axon collaterals to the other regions. However, it remains to be clarified how each STN neuron projects axon fibers and collaterals to those target nuclei of the STN. Here we visualized the whole axonal arborization of single STN neurons in the rat brain by using a viral vector expressing membrane‐targeted green fluorescent protein, and examined the distribution of axon boutons in those target nuclei. The vast majority (8–9) of 10 reconstructed STN neurons projected to the GPe, SN, caudate‐putamen (CPu), and Ep, which received, on average ± SD, 457 ± 425, 400 ± 347, 126 ± 143, and 106 ± 100 axon boutons per STN neuron, respectively. Furthermore, the density of axon boutons in the GPe was highest among these nuclei. Although these target nuclei were divided into calbindin‐rich and ‐poor portions, STN projection showed no exclusive preference for those portions. Since STN neurons mainly projected not only to the GPe, SN, and Ep but also to the CPu, the subthalamostriatal projection might serve as a positive feedback path for the striato‐GPe‐subthalamic disinhibitory pathway, or work as another route of cortical inputs to the striatum through the corticosubthalamostriatal disynaptic excitatory pathway. J. Comp. Neurol. 521:2125–2146, 2013. © 2012 Wiley Periodicals, Inc.     

Cholinergic innervation of principal neurons in the cochlear nucleus of the Mongolian gerbil

Principal neurons in the ventral cochlear nucleus (VCN) receive powerful ascending excitation and pass on the auditory information with exquisite temporal fidelity. Despite being dominated by ascending inputs, the VCN also receives descending cholinergic connections from olivocochlear neurons and from higher regions in the pontomesencephalic tegmentum. In Mongolian gerbils, acetylcholine acts as an excitatory and modulatory neurotransmitter on VCN neurons, but the anatomical structure of cholinergic innervation of gerbil VCN is not well described. We applied fluorescent immunohistochemical staining to elucidate the development and the cellular localization of presynaptic and postsynaptic components of the cholinergic system in the VCN of the Mongolian gerbil. We found that cholinergic fibers (stained with antibodies against the vesicular acetylcholine transporter) were present before hearing onset at P5, but innervation density increased in animals after P10. Early in development cholinergic fibers invaded the VCN from the medial side, spread along the perimeter and finally innervated all parts of the nucleus only after the onset of hearing. Cholinergic fibers ran in a rostro‐caudal direction within the nucleus and formed en‐passant swellings in the neuropil between principal neurons. Nicotinic and muscarinic receptors were expressed differentially in the VCN, with nicotinic receptors being mostly expressed in dendritic areas while muscarinic receptors were located predominantly in somatic membranes. These anatomical data support physiological indications that cholinergic innervation plays a role in modulating information processing in the cochlear nucleus.