Loss of Ephaptic Contacts in the Murine Thalamus during Osmotic Demyelination Syndrome.

BACKGROUND AND AIM: A murine model mimicking osmotic demyelination syndrome (ODS) revealed with histology in the relay posterolateral (VPL) and ventral posteromedial (VPM) thalamic nuclei adjoined nerve cell bodies in chronic hyponatremia, amongst the damaged 12 h and 48 h after reinstatement of osmolality. This report aims to verify and complement with ultrastructure other neurophysiology, immunohistochemistry, and molecular biochemistry data to assess the connexin-36 protein, as part of those hinted close contacts.This ODS investigation included four groups of mice: Sham (NN; n = 13), hyponatremic (HN; n = 11), those sacrificed 12 h after a fast restoration of normal natremia (ODS12h; n = 6) and mice sacrificed 48 h afterward, or ODS48 h (n = 9). Out of these, thalamic zones samples included NN (n = 2), HN (n = 2), ODS12h (n = 3) and ODS48h (n = 3). RESULTS: Ultrastructure illustrated junctions between nerve cell bodies that were immunolabeled with connexin36 (Cx36) with light microscopy and Western blots. These cell's junctions were reminiscent of low resistance junctions characterized in other regions of the CNS with electrophysiology. Contiguous neurons showed neurolemma contacts in intact and damaged tissues according to their location in the ODS zones, at 12 h and 48 h post correction along with other demyelinating alterations. Neurons and ephaptic contact measurements indicated the highest alterations, including nerve cell necrosis in the ODS epicenter and damages decreased toward the outskirts of the demyelinated zone. CONCLUSION: Ephapses contained C × 36between intact or ODS injured neurons in the thalamus appeared to be resilient beyond the core degraded tissue injuries. These could maintain intercellular ionic and metabolite exchanges between these lesser injured regions and, thus, would partake to some brain plasticity repairs.

Thalamocortical axons regulate neurogenesis and laminar fates in the early sensory cortex.

Area-specific axonal projections from the mammalian thalamus shape unique cellular organization in target areas in the adult neocortex. How these axons control neurogenesis and early neuronal fate specification is poorly understood. By using mutant mice lacking the majority of thalamocortical axons, we show that these axons are required for the production and specification of the proper number of layer 4 neurons in primary sensory areas by the neonatal stage. Part of these area-specific roles is played by the thalamus-derived molecule, VGF. Our work reveals that extrinsic cues from sensory thalamic projections have an early role in the formation of cortical cytoarchitecture by enhancing the production and specification of layer 4 neurons.

Whole brain and deep gray matter structure segmentation: Quantitative comparison between MPRAGE and MP2RAGE sequences.

OBJECTIVE: T1-weighted MRI images are commonly used for volumetric assessment of brain structures. Magnetization prepared 2 rapid gradient echo (MP2RAGE) sequence offers superior gray (GM) and white matter (WM) contrast. This study aimed to quantitatively assess the agreement of whole brain tissue and deep GM (DGM) volumes obtained from MP2RAGE compared to the widely used MP-RAGE sequence. METHODS: Twenty-nine healthy participants were included in this study. All subjects underwent a 3T MRI scan acquiring high-resolution 3D MP-RAGE and MP2RAGE images. Twelve participants were re-scanned after one year. The whole brain, as well as DGM segmentation, was performed using CAT12, volBrain, and FSL-FAST automatic segmentation tools based on the acquired images. Finally, contrast-to-noise ratio between WM and GM (CNRWG), the agreement between the obtained tissue volumes, as well as scan-rescan variability of both sequences were explored. RESULTS: Significantly higher CNRWG was detected in MP2RAGE vs. MP-RAGE (Mean ± SD = 0.97 ± 0.04 vs. 0.8 ± 0.1 respectively; p<0.0001). Significantly higher total brain GM, and lower cerebrospinal fluid volumes were obtained from MP2RAGE vs. MP-RAGE based on all segmentation methods (p<0.05 in all cases). Whole-brain voxel-wise comparisons revealed higher GM tissue probability in the thalamus, putamen, caudate, lingual gyrus, and precentral gyrus based on MP2RAGE compared with MP-RAGE. Moreover, significantly higher WM probability was observed in the cerebellum, corpus callosum, and frontal-and-temporal regions in MP2RAGE vs. MP-RAGE. Finally, MP2RAGE showed a higher mean percentage of change in total brain GM compared to MP-RAGE. On the other hand, MP-RAGE demonstrated a higher overtime percentage of change in WM and DGM volumes compared to MP2RAGE. CONCLUSIONS: Due to its higher CNR, MP2RAGE resulted in reproducible brain tissue segmentation, and thus is a recommended method for volumetric imaging biomarkers for the monitoring of neurological diseases.

Comparative Ultrastructural Analysis of Thalamocortical Innervation of the Primary Motor Cortex and Supplementary Motor Area in Control and MPTP-Treated Parkinsonian Monkeys.

The synaptic organization of thalamic inputs to motor cortices remains poorly understood in primates. Thus, we compared the regional and synaptic connections of vGluT2-positive thalamocortical glutamatergic terminals in the supplementary motor area (SMA) and the primary motor cortex (M1) between control and MPTP-treated parkinsonian monkeys. In controls, vGluT2-containing fibers and terminal-like profiles invaded layer II-III and Vb of M1 and SMA. A significant reduction of vGluT2 labeling was found in layer Vb, but not in layer II-III, of parkinsonian animals, suggesting a potential thalamic denervation of deep cortical layers in parkinsonism. There was a significant difference in the pattern of synaptic connectivity in layers II-III, but not in layer Vb, between M1 and SMA of control monkeys. However, this difference was abolished in parkinsonian animals. No major difference was found in the proportion of perforated versus macular post-synaptic densities at thalamocortical synapses between control and parkinsonian monkeys in both cortical regions, except for a slight increase in the prevalence of perforated axo-dendritic synapses in the SMA of parkinsonian monkeys. Our findings suggest that disruption of the thalamic innervation of M1 and SMA may underlie pathophysiological changes of the motor thalamocortical loop in the state of parkinsonism.

The osmotic demyelination syndrome: the resilience of thalamic neurons is verified with transmission electron microscopy.

The development of a murine model of osmotic demyelinating syndrome (ODS) allowed to study changes incurred in extrapontine zones of the CNS and featured neuron and glial cell changes in the relay thalamic ventral posterolateral (VPL) and ventral posteromedial (VPM) nuclei before, during and after ODS induction, and characterized without immune response. There, the neuron Wallerian-type deteriorations were verified with fine structure modifications of the neuron cell body, including some nucleus topology and its nucleolus changes. Morphologic analyses showed a transient stoppage of transcriptional activities while myelinated axons in the surrounding neuropil incurred diverse damages, previously reported. Even though the regional thalamus myelin deterioration was clearly recognized with light microscopy 248 h after osmotic recovery of ODS, ultrastructure analyses demonstrated that, at that time, the same damaged parenchyma regions contained nerve cell bodies that have already reactivated nucleus transcriptions and neuroplasm translations because peculiar accumulations of fibro-granular materials, similar to those detected in restored ODS astrocytes, were revealed in these restructuring nerve cell bodies. Their aspects suggested to be accumulations of ribonucleoproteins. The findings suggested that progressive neural function's recovery in the murine model could imitate some aspects of human ODS recovery cases.

Group I metabotropic glutamate receptors in the primate motor thalamus: subsynaptic association with cortical and sub-cortical glutamatergic afferents.

Preclinical evidence indicates that mGluR5 is a potential therapeutic target for Parkinson's disease and L-DOPA-induced dyskinesia. However, the mechanisms through which these therapeutic benefits are mediated remain poorly understood. Although the regulatory role of mGluR5 on glutamatergic transmission has been examined in various basal ganglia nuclei, very little is known about the localization and function of mGluR5 in the ventral motor and intralaminar thalamic nuclei, the main targets of basal ganglia output in mammals. Thus, we used immuno-electron microscopy to map the cellular and subcellular localization of group I mGluRs (mGluR1a and mGluR5) in the ventral motor and caudal intralaminar thalamic nuclei in rhesus monkeys. Furthermore, using double immuno-electron microscopy, we examined the subsynaptic localization of mGluR5 in relation to cortical and sub-cortical glutamatergic afferents. Four major conclusions can be drawn from these data. First, mGluR1a and mGluR5 are expressed postsynaptically on the plasma membrane of dendrites of projection neurons and GABAergic interneurons in the basal ganglia- and cerebellar-receiving regions of the ventral motor thalamus and in CM. Second, the plasma membrane-bound mGluR5 immunoreactivity is preferentially expressed perisynaptically at the edges of cortical and sub-cortical glutamatergic afferents. Third, the mGluR5 immunoreactivity is more strongly expressed in the lateral than the medial tiers of CM, suggesting a preferential association with thalamocortical over thalamostriatal neurons in the primate CM. Overall, mGluR5 is located to subserve powerful modulatory role of cortical and subcortical glutamatergic transmission in the primate ventral motor thalamus and CM.

Ultrastructure of giant thalamic terminals in the auditory cortex.

The auditory system comprises some very large axonal terminals like the endbulb and calyx of Held and "giant" corticothalamic synapses. Previously, we described a hitherto unknown population of giant thalamocortical boutons arising from the medial division of the medial geniculate body (MGm) in the Mongolian gerbil, which terminate over a wide cortical range but in a columnar manner particularly in the extragranular layers of the auditory cortex. As a first step towards an understanding of their potential functional role, we here describe their ultrastructure combining anterograde tract-tracing with biocytin and electron microscopy. Quantitative ultrastructural analyses revealed that biocytin-labelled MGm boutons reach much larger sizes than other, non-labelled boutons. Also, mitochondria occupy more space within labelled boutons whereas synapses are of similar size. Labelled boutons are very heterogeneous in size but homogeneous with respect to their ultrastructural characteristics, with asymmetric synapses containing clear, round vesicles and targeting dendritic spines. Functionally, the ultrastructure of the MGm terminals indicates that they form excitatory contacts, which may transmit their information in a rapid, powerful and high-fidelity manner onto strategically advantageous compartments of their cortical target cells.

Ultrastructural Analysis of Thalamus Damages in a Mouse Model of Osmotic-Induced Demyelination.

A murine model used to investigate the osmotic demyelination syndrome (ODS) demonstrated ultrastructural damages in thalamus nuclei. Following chronic hyponatremia, significant myelinolysis was merely detected 48 h after the rapid reinstatement of normonatremia (ODS 48 h). In ODS samples, oligodendrocytes and astrocytes revealed injurious changes associated with a few cell deaths while both cell types seemed to endure a sort of survival strategy: (a) ODS 12 h oligodendrocytes displayed nucleoplasm with huge heterochromatic compaction, mitochondria hypertrophy, and most reclaimed an active NN cell aspect at ODS 48 h. (b) Astrocytes responded to the osmotic stress by overall cell shrinkage with clasmatodendrosis, these changes accompanied nucleus wrinkling, compacted and segregated nucleolus, destabilization of astrocyte-oligodendrocyte junctions, loss of typical GFAP filaments, and detection of round to oblong woolly, proteinaceous aggregates. ODS 48 h astrocytes regained an active nucleus aspect, without restituting GFAP filaments and still contained cytoplasmic proteinaceous deposits. (c) Sustaining minor shrinking defects at ODS 12 h, neurons showed slight axonal injury. At ODS 48 h, neuron cell bodies emerged again with deeply indented nucleus and, owing nucleolus translational activation, huge amounts of polysomes along with secretory-like activities. (d) In ODS, activated microglial cells got stuffed with huge lysosome bodies out of captures cell damages, leaving voids in interfascicular and sub-vascular neuropil. Following chronic hyponatremia, the murine thalamus restoration showed macroglial cells acutely turned off transcriptional and translational activities during ODS and progressively recovered activities, unless severely damaged cells underwent cell death, leading to neuropil disruption and demyelination.

Distribution and Morphology of Cortical Terminals in the Cat Thalamus from the Anterior Ectosylvian Sulcus.

Two main types of cortical terminals have been identified in the cat thalamus. Large (type II) have been proposed to drive the response properties of thalamic cells while smaller (type I) are believed to modulate those properties. Among the cat's visual cortical areas, the anterior ectosylvian visual area (AEV) is considered as one of the highest areas in the hierarchical organization of the visual system. Whereas the connections from the AEV to the thalamus have been recognized, their nature (type I or II) is presently not known. In this study, we assessed and compared the relative contribution of type I and type II inputs to thalamic nuclei originating from the AEV. The anterograde tracer BDA was injected in the AEV of five animals. Results show that (1) both type I and II terminals from AEV are present in the Lateral Posterior- Pulvinar complex, the lateral median suprageniculate complex and the medial and dorsal geniculate nuclei (2) type I terminals significantly outnumber the type II terminals in almost all nuclei studied. Our results indicate that neurons in the AEV are more likely to modulate response properties in the thalamus rather than to determine basic organization of receptive fields of thalamic cells.

Major Feedforward Thalamic Input Into Layer 4C of Primary Visual Cortex in Primate.

One of the underlying principles of how mammalian circuits are constructed is the relative influence of feedforward to recurrent synaptic drive. It has been dogma in sensory systems that the thalamic feedforward input is relatively weak and that there is a large amplification of the input signal by recurrent feedback. Here we show that in trichromatic primates there is a major feedforward input to layer 4C of primary visual cortex. Using a combination of 3D-electron-microscopy and 3D-confocal imaging of thalamic boutons we found that the average feedforward contribution was about 20% of the total excitatory input in the parvocellular (P) pathway, about 3 times the currently accepted values for primates. In the magnocellular (M) pathway it was around 15%, nearly twice the currently accepted values. New methods showed the total synaptic and cell densities were as much as 150% of currently accepted values. The new estimates of contributions of feedforward synaptic inputs into visual cortex call for a major revision of the design of the canonical cortical circuit.

Ultrahigh-Magnitude Brain Magnetic Resonance Imaging Scan on Rhesus Monkeys With Implanted Deep Brain Stimulation Hardware.

BACKGROUND: Patients with implanted deep brain stimulation (DBS) hardware are prohibited from undergoing magnetic resonance imaging (MRI) scans at magnitudes greater than 1.5 T to avoid potential MRI-related heating injury. Whether DBS devices are compatible with higher field MRI scanning is unknown. This study aimed to investigate whether 7.0 T and 3.0 T MRI scans can be safely performed on rhesus monkeys with implanted DBS devices. METHODS: Eight male rhesus monkeys were included in this study and stereotactically implanted with DBS devices in the left anterior thalamus. Two weeks after DBS device implantation, 7.0 T and 3.0 T MRI scans were performed. The monkeys were observed for 72 hours. After explantation of the DBS system, 7.0 T MRI was repeated to determine potential lesions. Hematoxylin and eosin staining and transmission electron microscopy were conducted to assess pathological alterations. RESULTS: In both groups, the monkeys exhibited no behavioral changes related to neurological deficits. Post-explantation MRI showed no malacia foci surrounding the DBS tracks. Additionally, neither hematoxylin and eosin staining nor transmission electron microscopy showed clear injury near the DBS leads. CONCLUSION: These results indicate that no obvious heating injury was induced in the tissue surrounding the DBS leads by the 7.0 T and 3.0 T MRI scans. Although the results of this study may not be generalizable, these data suggest that patients with implanted DBS devices can undergo even 7.0 T MRI without risk of brain injury.

Infrabarrels Are Layer 6 Circuit Modules in the Barrel Cortex that Link Long-Range Inputs and Outputs.

The rodent somatosensory cortex includes well-defined examples of cortical columns-the barrel columns-that extend throughout the cortical depth and are defined by discrete clusters of neurons in layer 4 (L4) called barrels. Using the cell-type-specific Ntsr1-Cre mouse line, we found that L6 contains infrabarrels, readily identifiable units that align with the L4 barrels. Corticothalamic (CT) neurons and their local axons cluster within the infrabarrels, whereas corticocortical (CC) neurons are densest between infrabarrels. Optogenetic experiments showed that CC cells received robust input from somatosensory thalamic nuclei, whereas CT cells received much weaker thalamic inputs. We also found that CT neurons are intrinsically less excitable, revealing that both synaptic and intrinsic mechanisms contribute to the low firing rates of CT neurons often reported in vivo. In summary, infrabarrels are discrete cortical circuit modules containing two partially separated excitatory networks that link long-distance thalamic inputs with specific outputs.

Consequences of perinatal hypoxia in developing brain: Changes in GABA transporter functioning in cortical, hippocampal and thalamic rat nerve terminals.

Perinatal hypoxia leads to behavioral abnormalities, cognitive disabilities, and epilepsy resulting from alterations in neurodevelopment, maturation and construction of the network. Considering a particular role of γ-aminobutyric acid (GABA) for an immature brain, we analysed transporter-mediated [3H]GABA uptake in the cortical, hippocampal and thalamic nerve terminals isolated from rats of different age in the control and after perinatal hypoxia. The state of hypoxia was induced by exposure of rats at the age of 10 postnatal days (pd) (that corresponds approximately to the time of birth in humans) to a respiratory medium with low O2 content (4% O2 and 96%N2) for 12min (up to the initiation of clonico-tonic seizures). Here, we found that the initial rate of [3Н]GABA uptake was higher in the young rats (pd 17-19) as compared to the older ones (pd 24-26, 38-40 and 66-73) in both control and hypoxia groups. It decreased abruptly by 50% in the thalamus and by 25% in the cortex for the period from pd 17-19 to pd 66-73. In the hippocampus, a decrease in the rate during the same time interval was 25%. Exposure to hypoxia had no effect on the intensity of [3Н]GABA uptake by the cortical and thalamic nerve terminals, but caused a significant age-dependent attenuation (by 35%) of the uptake intensity in the hippocampal ones. Significant age-dependent hypoxia-independent decrease in [3Н]GABA uptake with step-like dynamics of changes was shown in the thalamus and cortex. Gradual age-dependent hypoxia-dependent decrease in [3Н]GABA uptake was revealed in the hippocampus, and so a particular vulnerability of the latest structure to hypoxia as compared to the cortex and thalamus was revealed.

Effects of epidural compression on stellate neurons and thalamocortical afferent fibers in the rat primary somatosensory cortex.

A number of neurological disorders such as epidural hematoma can cause compression of cerebral cortex. We here tested the hypothesis that sustained compression of primary somatosensory cortex may affect stellate neurons and thalamocortical afferent (TCA) fibers. A rat model with barrel cortex subjected to bead epidural compression was used. Golgi-Cox staining analyses showed the shrinkage of dendritic arbors and the stripping of dendritic spines of stellate neurons for at least 3 months post-lesion. Anterograde tracing analyses exhibited a progressive decline of TCA fiber density in barrel field for 6 months post-lesion. Due to the abrupt decrease of TCA fiber density at 3 days after compression, we further used electron microscopy to investigate the ultrastructure of TCA fibers at this time. Some TCA fiber terminal profiles with dissolved or darkened mitochondria and fewer synaptic vesicles were distorted and broken. Furthermore, the disruption of mitochondria and myelin sheath was observed in some myelinated TCA fibers. In addition, expressions of oxidative markers 3-nitrotyrosine and 4-hydroxynonenal were elevated in barrel field post-lesion. Treatment of antioxidant ascorbic acid or apocynin was able to reverse the increase of oxidative stress and the decline of TCA fiber density, rather than the shrinkage of dendrites and the stripping of dendritic spines of stellate neurons post-lesion. Together, these results indicate that sustained epidural compression of primary somatosensory cortex affects the TCA fibers and the dendrites of stellate neurons for a prolonged period. In addition, oxidative stress is responsible for the reduction of TCA fiber density in barrels rather than the shrinkage of dendrites and the stripping of dendritic spines of stellate neurons.

An Ultrastructural Study of the Thalamic Input to Layer 4 of Primary Motor and Primary Somatosensory Cortex in the Mouse.

The traditional classification of primary motor cortex (M1) as an agranular area has been challenged recently when a functional layer 4 (L4) was reported in M1. L4 is the principal target for thalamic input in sensory areas, which raises the question of how thalamocortical synapses formed in M1 in the mouse compare with those in neighboring sensory cortex (S1). We identified thalamic boutons by their immunoreactivity for the vesicular glutamate transporter 2 (VGluT2) and performed unbiased disector counts from electron micrographs. We discovered that the thalamus contributed proportionately only half as many synapses to the local circuitry of L4 in M1 compared with S1. Furthermore, thalamic boutons in M1 targeted spiny dendrites exclusively, whereas ∼9% of synapses were formed with dendrites of smooth neurons in S1. VGluT2+ boutons in M1 were smaller and formed fewer synapses per bouton on average (1.3 vs 2.1) than those in S1, but VGluT2+ synapses in M1 were larger than in S1 (median postsynaptic density areas of 0.064 µm2 vs 0.042 µm2). In M1 and S1, thalamic synapses formed only a small fraction (12.1% and 17.2%, respectively) of all of the asymmetric synapses in L4. The functional role of the thalamic input to L4 in M1 has largely been neglected, but our data suggest that, as in S1, the thalamic input is amplified by the recurrent excitatory connections of the L4 circuits. The lack of direct thalamic input to inhibitory neurons in M1 may indicate temporal differences in the inhibitory gating in L4 of M1 versus S1.SIGNIFICANCE STATEMENT Classical interpretations of the function of primary motor cortex (M1) emphasize its lack of the granular layer 4 (L4) typical of sensory cortices. However, we show here that, like sensory cortex (S1), mouse M1 also has the canonical circuit motif of a core thalamic input to the middle cortical layer and that thalamocortical synapses form a small fraction (M1: 12%; S1: 17%) of all asymmetric synapses in L4 of both areas. Amplification of thalamic input by recurrent local circuits is thus likely to be a significant mechanism in both areas. Unlike M1, where thalamocortical boutons typically form a single synapse, thalamocortical boutons in S1 usually formed multiple synapses, which means they can be identified with high probability in the electron microscope without specific labeling.

The short- and long-term proteomic effects of sleep deprivation on the cortical and thalamic synapses.

Acute total sleep deprivation (SD) impairs memory consolidation, attention, working memory and perception. Structural, electrophysiological and molecular experimental approaches provided evidences for the involvement of sleep in synaptic functions. Despite the wide scientific interest on the effects of sleep on the synapse, there is a lack of systematic investigation of sleep-related changes in the synaptic proteome. We isolated parietal cortical and thalamic synaptosomes of rats after 8h of total SD by gentle handling and 16h after the end of deprivation to investigate the short- and longer-term effects of SD on the synaptic proteome, respectively. The SD efficiency was verified by electrophysiology. Protein abundance alterations of the synaptosomes were analyzed by fluorescent two-dimensional differential gel electrophoresis and by tandem mass spectrometry. As several altered proteins were found to be involved in synaptic strength regulation, our data can support the synaptic homeostasis hypothesis function of sleep and highlight the long-term influence of SD after the recovery sleep period, mostly on cortical synapses. Furthermore, the large-scale and brain area-specific protein network change in the synapses may support both ideas of sleep-related synaptogenesis and molecular maintenance and reorganization in normal rat brain.

Sub-synaptic localization of Cav3.1 T-type calcium channels in the thalamus of normal and parkinsonian monkeys.

T-type calcium channels (Cav3) are key mediators of thalamic bursting activity, but also regulate single cells excitability, dendritic integration, synaptic strength and transmitter release. These functions are strongly influenced by the subcellular and subsynaptic localization of Cav3 channels along the somatodendritic domain of thalamic cells. In Parkinson's disease, T-type calcium channels dysfunction in the basal ganglia-receiving thalamic nuclei likely contributes to pathological thalamic bursting activity. In this study, we analyzed the cellular, subcellular, and subsynaptic localization of the Cav3.1 channel in the ventral anterior (VA) and centromedian/parafascicular (CM/Pf) thalamic nuclei, the main thalamic targets of basal ganglia output, in normal and parkinsonian monkeys. All thalamic nuclei displayed strong Cav3.1 neuropil immunoreactivity, although the intensity of immunolabeling in CM/Pf was significantly lower than in VA. Ultrastructurally, 70-80 % of the Cav3.1-immunoreactive structures were dendritic shafts. Using immunogold labeling, Cav3.1 was commonly found perisynaptic to asymmetric and symmetric axo-dendritic synapses, suggesting a role of Cav3.1 in regulating excitatory and inhibitory neurotransmission. Significant labeling was also found at non-synaptic sites along the plasma membrane of thalamic neurons. There was no difference in the overall pattern and intensity of immunostaining between normal and parkinsonian monkeys, suggesting that the increased rebound bursting in the parkinsonian state is not driven by changes in Cav3.1 expression. Thus, T-type calcium channels are located to subserve neuronal bursting, but also regulate glutamatergic and non-glutamatergic transmission along the whole somatodendritic domain of basal ganglia-receiving neurons of the primate thalamus.

Maternally involved galanin neurons in the preoptic area of the rat.

Recent selective stimulation and ablation of galanin neurons in the preoptic area of the hypothalamus established their critical role in control of maternal behaviors. Here, we identified a group of galanin neurons in the anterior commissural nucleus (ACN), and a distinct group in the medial preoptic area (MPA). Galanin neurons in ACN but not the MPA co-expressed oxytocin. We used immunodetection of phosphorylated STAT5 (pSTAT5), involved in prolactin receptor signal transduction, to evaluate the effects of suckling-induced prolactin release and found that 76 % of galanin cells in ACN, but only 12 % in MPA were prolactin responsive. Nerve terminals containing tuberoinfundibular peptide 39 (TIP39), a neuropeptide that mediates effects of suckling on maternal motivation, were abundant around galanin neurons in both preoptic regions. In the ACN and MPA, 89 and 82 % of galanin neurons received close somatic appositions, with an average of 2.9 and 2.6 per cell, respectively. We observed perisomatic innervation of galanin neurons using correlated light and electron microscopy. The connection was excitatory based on the glutamate content of TIP39 terminals demonstrated by post-embedding immunogold electron microscopy. Injection of the anterograde tracer biotinylated dextran amine into the TIP39-expressing posterior intralaminar complex of the thalamus (PIL) demonstrated that preoptic TIP39 fibers originate in the PIL, which is activated by suckling. Thus, galanin neurons in the preoptic area of mother rats are innervated by an excitatory neuronal pathway that conveys suckling-related information. In turn, they can be topographically and neurochemically divided into two distinct cell groups, of which only one is affected by prolactin.

Tectothalamic inhibitory projection neurons in the avian torus semicircularis.

Inhibitory feedforward projection is one of key features of the organization of the central auditory system. In mammals, the inferior colliculus (IC) is the origin of a substantial inhibitory feedforward projection as well as an excitatory projection to the auditory thalamus. This inhibitory feedforward projection is provided by large γ-aminobutyric acid (GABA)ergic (LG) neurons, which are characterized by their receipt of dense excitatory axosomatic terminals positive for vesicular glutamate transporter (VGLUT) 2. In the avian torus semicircularis (TS), which is the homolog of the IC, neither the homology of cell types nor the presence of inhibitory feedforward inhibition have been established. In this study, we tested the presence of LG neurons in pigeon and chicken by neuroanatomical techniques. The TS contained two types of GABAergic neurons of different soma size. Of these, larger GABA + cells were encircled by dense VGLUT2 + axosomatic terminals. Ultrastructural analyses revealed that more than 30% of the perimeter of a large GABA+, but not small GABA + or GABA-, soma was covered by presumptive excitatory axosomatic terminals, suggesting that large GABA + cells are the sole recipient of dense excitatory axosomatic synapses. After injection of a retrograde tracer into the auditory thalamus, many retrogradely labeled neurons were found bilaterally in the TS, a few of which were GABA+. Almost all tectothalamic GABA + neurons had large somata, and received dense VGLUT2 + axosomatic terminals. These results clearly demonstrated the presence of LG neurons in birds. The similar morphology of LG neurons implies that the function of tectothalamic inhibition is similar among amniotes. J. Comp. Neurol. 524:2604-2622, 2016. © 2016 Wiley Periodicals, Inc.

The vulnerability of thalamocortical circuitry to hypoxic-ischemic injury in a mouse model of periventricular leukomalacia.

BACKGROUND: Periventricular leukomalacia (PVL) is the leading cause of neurological disabilities including motor and cognitive deficits in premature infants. Periventricular leukomalacia is characterized by damage to the white matter in the immature brain, but the mechanisms by which damage to immature white matter results in widespread deficits of cognitive and motor function are unclear. The thalamocortical system is crucial for human consciousness and cognitive functions, and impaired development of the cortico-thalamic projections in the neonatal period is implicated to contribute importantly to abnormalities of cognitive function in children with PVL. RESULTS: In this study, using a mouse model of PVL, we sought to test the hypothesis that PVL-like injury affects the different components of the thalamocortical circuitry that can be defined by vesicular glutamate transporters 1 and 2 (vGluT1 and vGluT2), both of which are required for glutamatergic synaptic transmission in the central nervous system. We combined immunocytochemistry and immuno-electron microscopy to investigate changes in cortico-thalamic synapses which were specifically identified by vGluT1 immunolabeling. We found that a drastic reduction in the density of vGluT1 labeled profiles in the somatosensory thalamus, with a reduction of 72-74 % in ventroposterior (VP) nucleus and a reduction of 42-82 % in thalamic reticular nucleus (RTN) in the ipsilateral side of PVL mice. We further examined these terminals at the electron microscopic level and revealed onefold-twofold decrease in the sizes of vGluT1 labeled corticothalamic terminals in VP and RTN. The present study provides anatomical and ultrastructural evidence to elucidate the cellular mechanisms underlying alteration of thalamic circuitry in a mouse model of PVL, and reveals that PVL-like injury has a direct impact on the corticothalamic projection system. CONCLUSIONS: Our findings provide the first set of evidence showing that the thalamocortical circuitry is affected and vulnerable in PVL mice, supporting a working model in which vGluT1 defined corticothalamic synapses are altered in PVL mice, and vGluT2 defined thalamocortical synapses are associated with such changes, leading to the compromised thalamocortical circuitry in the PVL mice. Our study demonstrates that the thalamocortical circuitry is highly vulnerable to hypoxia-ischemia in the PVL model, thus identifying a novel target site in PVL pathology.