Local NMDA Receptor Blockade Attenuates Chronic Tinnitus and Associated Brain Activity in an Animal Model

Chronic tinnitus has no broadly effective treatment. Identification of specific markers for tinnitus should facilitate the development of effective therapeutics. Recently it was shown that glutamatergic blockade in the cerebellar paraflocculus, using an antagonist cocktail was successful in reducing chronic tinnitus. The present experiment examined the effect of selective N-methyl d-aspartate (NMDA) receptor blockade on tinnitus and associated spontaneous brain activity in a rat model. The NMDA antagonist, D(−)-2-amino-5-phosphonopentanoic acid (D-AP5) (0.5 mM), was continuously infused for 2 weeks directly to the ipsilateral paraflocculus of rats with tinnitus induced months prior by unilateral noise exposure. Treated rats were compared to untreated normal controls without tinnitus, and to untreated positive controls with tinnitus. D-AP5 significantly decreased tinnitus within three days of beginning treatment, and continued to significantly reduce tinnitus throughout the course of treatment and for 23 days thereafter, at which time testing was halted. At the conclusion of psychophysical testing, neural activity was assessed using manganese enhanced magnetic resonance imaging (MEMRI). In agreement with previous research, untreated animals with chronic tinnitus showed significantly elevated bilateral activity in their paraflocculus and brainstem cochlear nuclei, but not in mid or forebrain structures. In contrast, D-AP5-treated-tinnitus animals showed significantly less bilateral parafloccular and dorsal cochlear nucleus activity, as well as significantly less contralateral ventral cochlear nucleus activity. It was concluded that NMDA-mediated glutamatergic transmission in the paraflocculus appears to be a necessary component of chronic noise-induced tinnitus in a rat model. Additionally, it was confirmed that in this model, elevated spontaneous activity in the cerebellar paraflocculus and auditory brainstem is associated with tinnitus.     

Golgi Cell-Mediated Activation of Postsynaptic GABA(B) Receptors Induces Disinhibition of the Golgi Cell-Granule Cell Synapse in Rat Cerebellum

In the cerebellar glomerulus, GABAergic synapses formed by Golgi cells regulate excitatory transmission from mossy fibers to granule cells through feed-forward and feedback mechanisms. In acute cerebellar slices, we found that stimulating Golgi cell axons with a train of 10 impulses at 100 Hz transiently inhibited both the phasic and the tonic components of inhibitory responses recorded in granule cells. This effect was blocked by the GABA(B) receptor blocker CGP35348, and could be mimicked by bath-application of baclofen (30 μM). This depression of IPSCs was prevented when granule cells were dialyzed with GDPβS. Furthermore, when synaptic transmission was blocked, GABA(A) currents induced in granule cells by localized muscimol application were inhibited by the GABA(B) receptor agonist baclofen. These findings indicate that postsynaptic GABA(B) receptors are primarily responsible for the depression of IPSCs. This inhibition of inhibitory events results in an unexpected excitatory action by Golgi cells on granule cell targets. The reduction of Golgi cell-mediated inhibition in the cerebellar glomerulus may represent a regulatory mechanism to shift the balance between excitation and inhibition in the glomerulus during cerebellar information processing.     

Unipolar brush cells develop a set of characteristic features in primary cerebellar cultures

Brain Cell Biology - The unipolar brush cells (UBCs) are a class of excitatory interneurons recently discovered in the cerebellar granular layer. UBCs differ morphologically and biochemically from...     

Cultured subventricular zone progenitor cells transduced with neurogenin-2 become mature glutamatergic neurons and integrate into the dentate gyrus

We have previously shown that transplantation of immature DCX+/NeuN+/Prox1+ neurons (found in the neonatal DG), but not undifferentiated neuronal progenitor cells (NPCs) from ventral subventricular zone (SVZ), results in neuronal maturation in vivo within the dentate niche. Here we investigated whether we could enhance the integration of SVZ NPCs by forced expression of the proneural gene Neurogenin 2 (NEUROG2). NPCs cultured from neonatal GFP-transgenic rat SVZ for 7 days in a non-differentiating medium were transduced with a retrovirus encoding NEUROG2 and DsRed or the DsRed reporter gene alone (control). By 3 days post-transduction, the NEUROG2-transduced cells maintained in culture contained mostly immature neurons (91% DCX+; 76% NeuN+), whereas the control virus-transduced cells remained largely undifferentiated (30% DCX+; <1% NeuN+). At 6 weeks following transplantation into the DG of adult male rats, there were no neurons among the transplanted cells treated with the control virus but the majority of the NEUROG2-transduced DsRed+ SVZ cells became mature neurons (92% NeuN+; DCX-negative). Although the NEUROG2-transduced SVZ cells did not express the dentate granule neuron marker Prox1, most of the NEUROG2-transduced SVZ cells (78%) expressed the glutamatergic marker Tbr1, suggesting the acquisition of a glutamatergic phenotype. Moreover, some neurons extended dendrites into the molecular layer, grew axons containing Ankyrin G+ axonal initial segments, and projected into the CA3 region, thus resembling mature DG granule neurons. A proportion of NEUROG2 transduced cells also expressed c-Fos and P-CREB, two markers of neuronal activation. We conclude that NEUROG2-transduction is sufficient to promote neuronal maturation and integration of transplanted NPCs from SVZ into the DG.     

Developmental change and sexual difference in synaptic modulation produced by oxytocin in rat substantia gelatinosa neurons

We have previously reported that oxytocin produces an inward current at a holding potential of ?70 mV without a change in glutamatergic excitatory transmission in adult male rat spinal lamina II (substantia gelatinosa; SG) neurons that play a pivotal role in regulating nociceptive transmission. Oxytocin also enhanced GABAergic and glycinergic spontaneous inhibitory transmissions in a manner sensitive to a voltage-gated Na⁺-channel blocker tetrodotoxin. These actions were mediated by oxytocin-receptor activation. Such a result was different from that obtained by other investigators in young male rat superficial dorsal horn neurons in which an oxytocin-receptor agonist enhanced glutamatergic and GABAergic but not glycinergic spontaneous transmissions. In order to know a developmental change and also sexual difference in the actions of oxytocin, we examined its effect on spontaneous synaptic transmission in adult female and young male rat SG neurons by using the whole-cell patch-clamp technique in spinal cord slices. In adult female rats, oxytocin produced an inward current at ?70 mV without a change in excitatory transmission. GABAergic and glycinergic transmissions were enhanced by oxytocin, the duration of which enhancement was much shorter than in adult male rats. In young (11–21 postnatal days) male rats, oxytocin produced not only an inward but also outward current at ?70 mV, and presynaptically inhibited or facilitated excitatory transmission, depending on the neurons tested; both GABAergic and glycinergic transmissions were enhanced by oxytocin. The inhibitory transmission enhancements in adult female and young male rats were sensitive to tetrodotoxin. Although the data may not be enough to be estimated, it is suggested that synaptic modulation by oxytocin in SG neurons, i.e., cellular mechanism for its antinociceptive action, exhibits a developmental change and sexual difference.     

Depression of excitatory transmission at PF-PC synapse by group III metabotropic glutamate receptors is provided exclusively by mGluR4 in the rodent cerebellar cortex

In the rodent cerebellum, pharmacological activation of group III pre-synaptic metabotropic glutamate receptors (mGluRs) by the broad spectrum agonist l -2-amino-4-phosphonobutyric acid, acutely depresses excitatory synaptic transmission at parallel fiber (PF)-Purkinje cell (PC) synapses. Among the group III mGluR subtypes, cerebellar granule cells express predominantly mGluR4, but also mGluR7 and mGluR8 mRNA. Taking into account that previous functional and pharmacological studies have used group III mGluR broad spectrum agonists that do not differentiate between these various subtypes, their relative contribution to the modulation of glutamatergic transmission at PF-PC synapses remains to be elucidated. In order to clarify this issue, we applied conventional whole-cell patch-clamp recordings and pre-synaptic calcium influx measurements, combined with pharmacological manipulations to rat and mice cerebellar slices. With the use of (1 S ,2 R )-1-amino-2-phosphonomethylcyclopropanecarboxylic acid, a new and selective group III mGluR agonist, N -phenyl-7-(hydroxylimino)cyclopropa[b]-chromen-1a-carboxamide, the specific positive allosteric modulator of mGluR4, ( S )-3,4-dicarboxyphenylglycine, a selective mGluR8 agonist, and mGluR4 knock-out mice, we demonstrate that the inhibitory control of group III mGluRs on excitatory neurotransmission at PF-PC synapses of the rodent cerebellar cortex, is totally because of the activation of pre-synaptic mGluR4 autoreceptors.     

Properties of doublecortin expressing neurons in the adult mouse dentate gyrus

The dentate gyrus is a neurogenic zone where neurons continue to be born throughout life, mature and integrate into the local circuitry. In adults, this generation of new neurons is thought to contribute to learning and memory formation. As newborn neurons mature, they undergo a developmental sequence in which different stages of development are marked by expression of different proteins. Doublecortin (DCX) is an early marker that is expressed in immature granule cells that are beginning migration and dendritic growth but is turned off before neurons reach maturity. In the present study, we use a mouse strain in which enhanced green fluorescent protein (EGFP) is expressed under the control of the DCX promoter. We show that these neurons have high input resistances and some cells can discharge trains of action potentials. In mature granule cells, action potentials are followed by a slow afterhyperpolarization that is absent in EGFP-positive neurons. EGFP-positive neurons had a lower spine density than mature neurons and stimulation of either the medial or lateral perforant pathway activated dual component glutamatergic synapses that had both AMPA and NMDA receptors. NMDA receptors present at these synapses had slow kinetics and were blocked by ifenprodil, indicative of high GluN2B subunit content. These results show that EGFP-positive neurons in the DCX-EGFP mice are functionally immature both in their firing properties and excitatory synapses.     

Metabotropic glutamate receptors are associated with non-synaptic appendages of unipolar brush cells in rat cerebellar cortex and cochlear nuclear complex

Unipolar brush cells (UBCs) are a class of small neurons that are densely concentrated in the granular layers of the vestibulocerebellar cortex and dorsal cochlear nucleus. The UBCs form giant synapses with individual mossy fibre rosettes on the dendrioles which make up their brush formations and are provided with numerous, unusual non-synaptic appendages. In accord with the glutamatergic nature of mossy fibres, our previous post-embedding immunocytochemical studies indicated that various ionotropic glutamate receptor subunits are localized at the post-synaptic densities of the giant synapses, whereas the non-synaptic appendages are immunonegative. On the contrary, the metabotropic glutamate receptors mGluR1α and mGluR2/3 are situated at the non-synaptic appendages and are lacking at the post-synaptic densities. Other authors, however, have shown that antibodies to these metabotropic receptors stain both appendages and post-synaptic densities. In the present study, we have re-evaluated the distribution of metabotropic glutamate receptors in the UBCs of the cerebellum and the cochlear nuclear complex by light and electron microscopic pre-embedding immunocytochemistry with subtype-specific antibodies. We confirm that UBCs dendritic brushes are densely immunostained by antibody to mGluR1α particularly in the cerebellum and that antibody to mGluR2/3 labels at least a percentage of the UBC brushes in both the cerebellum and cochlear nuclei. At the ultrastructural level, it appears that mGluR1α and mGluR2/3 immunoreactivities are not associated with the post-synaptic densities of the giant mossy fibre–UBC synapses, but instead are concentrated on the non-synaptic appendages of the cerebellar UBCs. The non-synaptic appendages, therefore, may be an important avenue for regulating the excitability of UBCs and mediating glutamate effects on their still unknown intracellular signal transduction cascades. We also show that the pre-synaptic densities of UBC dendrodendritic junctions are mGluR2/3 positive. As previously demonstrated, antibodies to mGluR1 α and mGluR2/3 label subsets of Golgi cells. Antibody to mGluR5 does not stain UBCs in the cerebellum and cochlear nucleus and reveals the somatodendritic compartment of Golgi cells situated in the core of the cerebellar granular layer, whilst cochlear nucleus Golgi cells are mGluR5 negative.     

Arylamine toxins from funnel-web spider (Agelenopsis aperta) venom antagonize N-methyl-D-aspartate receptor function in mammalian brain.

The venom of the North American funnel-web spider Agelenopsis aperta contains a variety of arylamine toxins (the alpha-agatoxins) that paralyze insects by blocking glutamatergic neuromuscular transmission. We have tested six synthetic alpha-agatoxins for their ability to antagonize glutamate receptor function in mammalian brain. These compounds produce, at submicromolar concentrations, noncompetitive inhibition of N-methyl-D-aspartate (NMDA) receptor-mediated elevations in the concentration of cytosolic free calcium in cultured rat cerebellar granule neurons. In contrast, the alpha-agatoxins are relatively weak antagonists of elevations in the cytosolic free calcium concentration induced by non-NMDA receptor agonists. The alpha-agatoxins also produce reversible suppression of the NMDA receptor-mediated excitatory postsynaptic potential in rat hippocampal slices at concentrations that have little effect on the non-NMDA receptor-mediated population spike. We conclude that the alpha-agatoxins are selective and reversible noncompetitive antagonists at NMDA receptors in mammalian brain.     

The glutamatergic nature of TRPV1-expressing neurons in the spinal dorsal horn

The transient receptor potential vanilloid receptor 1 (TRPV1) is expressed on primary afferent terminals and spinal dorsal horn neurons. However, the neurochemical phenotypes and functions of TRPV1-expressing post-synaptic neurons in the spinal cord are not clear. In this study, we tested the hypothesis that TRPV1-expressing dorsal horn neurons are glutamatergic. Immunocytochemical labeling revealed that TRPV1 and vesicular glutamate transporter-2 were colocalized in dorsal horn neurons and their terminals in the rat spinal cord. Resiniferatoxin (RTX) treatment or dorsal rhizotomy ablated TRPV1-expressing primary afferents but did not affect TRPV1- and vesicular glutamate transporter-2-expressing dorsal horn neurons. Capsaicin significantly increased the frequency of glutamatergic spontaneous excitatory post-synaptic currents and miniature excitatory post-synaptic currents in almost all the lamina II neurons tested in control rats. In RTX-treated or dorsal rhizotomized rats, capsaicin still increased the frequency of spontaneous excitatory post-synaptic currents and miniature excitatory post-synaptic currents in the majority of neurons examined, and this effect was abolished by a TRPV1 blocker or by non-NMDA receptor antagonist. In RTX-treated or in dorsal rhizotomized rats, capsaicin also produced an inward current in a subpopulation of lamina II neurons. However, capsaicin had no effect on GABAergic and glycinergic spontaneous inhibitory post-synaptic currents of lamina II neurons in RTX-treated or dorsal rhizotomized rats. Collectively, our study provides new histological and functional evidence that TRPV1-expressing dorsal horn neurons in the spinal cord are glutamatergic and that they mediate excitatory synaptic transmission. This finding is important to our understanding of the circuitry and phenotypes of intrinsic dorsal horn neurons in the spinal cord.     

Effects of x-irradiation on the levels of glutamate,aspartate and GABA in different regions of the cerebellum of the rat

The effect of the x-irradiation-induced loss of cerebellar granule and stellate cells on the levels of glutamate, aspartate and GABA in regions of the rat cerebellum was determined. The level of glutamate was significantly lower in the neuron-depleted cerebellar cortex while GABA levels were higher than control values in the cerebellar cortex and white matter of the x-irradiated rats. Aspartate levels were not changed by x-irradiation in any cerebellar region. The data is discussed in terms of the proposed role of glutamate as the excitatory neurotransmitter released from granule cells.     

GABAA alpha6-containing receptors are selectively compromised in cerebellar granule cells of the ataxic mouse, stargazer

Stargazer mice fail to express the gamma2 isoform of transmembrane alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate (AMPA) receptor regulatory proteins that has been shown to be absolutely required for the trafficking and synaptic targeting of excitatory AMPA receptors in adult murine cerebellar granule cells. Here we show that 30 +/- 6% fewer inhibitory gamma-aminobutyric acid, type A (GABA(A)), receptors were expressed in adult stargazer cerebellum compared with controls because of a specific loss of GABA(A) receptor expression in the cerebellar granule cell layer. Radioligand binding assays allied to in situ immunogold-EM analysis and furosemide-sensitive tonic current estimates revealed that expression of the extrasynaptic (alpha6betaxdelta) alpha6-containing GABA(A) receptor were markedly and selectively reduced in stargazer. These observations were compatible with a marked reduction in expression of GABA(A) receptor alpha6, delta (mature cerebellar granule cell-specific proteins), and beta3 subunit expression in stargazer. The subunit composition of the residual alpha6-containing GABA(A) receptors was unaffected by the stargazer mutation. However, we did find evidence of an approximately 4-fold up-regulation of alpha1betadelta receptors that may compensate for the loss of alpha6-containing GABA(A) receptors. PCR analysis identified a dramatic reduction in the steady-state level of alpha6 mRNA, compatible with alpha6 being the primary target of the stargazer mutation-mediated GABA(A) receptor abnormalities. We propose that some aspects of assembly, trafficking, targeting, and/or expression of extrasynaptic alpha6-containing GABA(A) receptors in cerebellar granule cells are selectively regulated by AMPA receptor-mediated signaling.     

Ex Vivo Imaging of Postnatal Cerebellar Granule Cell Migration Using Confocal Macroscopy

During postnatal development, immature granule cells (excitatory interneurons) exhibit tangential migration in the external granular layer, and then radial migration in the molecular layer and the Purkinje cell layer to reach the internal granular layer of the cerebellar cortex. Default in migratory processes induces either cell death or misplacement of the neurons, leading to deficits in diverse cerebellar functions. Centripetal granule cell migration involves several mechanisms, such as chemotaxis and extracellular matrix degradation, to guide the cells towards their final position, but the factors that regulate cell migration in each cortical layer are only partially known. In our method, acute cerebellar slices are prepared from P10 rats, granule cells are labeled with a fluorescent cytoplasmic marker and tissues are cultured on membrane inserts from 4 to 10 hr before starting real-time monitoring of cell migration by confocal macroscopy at 37 °C in the presence of CO₂. During their migration in the different cortical layers of the cerebellum, granule cells can be exposed to neuropeptide agonists or antagonists, protease inhibitors, blockers of intracellular effectors or even toxic substances such as alcohol or methylmercury to investigate their possible role in the regulation of neuronal migration.     

Distribution of unipolar brush cells and other calretinin immunoreactive components in the mammalian cerebellar cortex

We have compared the distribution of unipolar brush cells (UBCs) in the cerebellum of Brazilian opossum (Monodelphis domestica), mouse, guinea pig, rabbit, cat, and Rhesus monkey, using an antiserum to calretinin which is present in those cells. The morphology and calretinin staining intensity of the UBCs remains constant across species. As a general trend, in all species studied, UBCs are particularly enriched in the vestibulocerebellum. Interspecies differences, however, were noted in the distribution of UBCs across other regions of the cerebellar cortex. A major variation involves the extent of the UBC-rich region of the ventral portion of the paraflocculus. The distribution of UBCs in non-vestibular vermal folia also varies substantially. UBCs are deployed in more or less distinct parasagittal zones in the vermis of the opossum, rabbit, cat, and macaque. The density of UBCs decreases progressively from medial to lateral portions of the same folium and is lowest in the lateral, posterior portions of the cerebellar hemispheres (crus II) and in the dorsal portion of the paraflocculus. In cat and macaque, the decrease in the density of UBCs across the intermediate cortex is more gradual than in the other species. The data indicate that the UBCs play a more prominent role in the modulation of sensorimotor transformations in carnivores and primates than in smaller mammals and should not be considered a vestigial form of neuron. In addition to the UBCs, calretinin antibody distinctly stains the following neurons in different species: granule cells and parallel fibers in all species except rabbit and cat; Golgi cells, especially in rat and macaque; Lugaro-like cells, especially in mouse, rat, and macaque; basket cells in macaque; subsets of mossy fibers in all species; and subsets of climbing fibers in all species but guinea pig. Usually, the distribution of UBCs is related to that of calretinin stained granule cells and mossy fibers.     

Determinants of synaptic integration and heterogeneity in rebound firing explored with data-driven models of deep cerebellar nucleus cells

Significant inroads have been made to understand cerebellar cortical processing but neural coding at the output stage of the cerebellum in the deep cerebellar nuclei (DCN) remains poorly understood. The DCN are unlikely to just present a relay nucleus because Purkinje cell inhibition has to be turned into an excitatory output signal, and DCN neurons exhibit complex intrinsic properties. In particular, DCN neurons exhibit a range of rebound spiking properties following hyperpolarizing current injection, raising the question how this could contribute to signal processing in behaving animals. Computer modeling presents an ideal tool to investigate how intrinsic voltage-gated conductances in DCN neurons could generate the heterogeneous firing behavior observed, and what input conditions could result in rebound responses. To enable such an investigation we built a compartmental DCN neuron model with a full dendritic morphology and appropriate active conductances. We generated a good match of our simulations with DCN current clamp data we recorded in acute slices, including the heterogeneity in the rebound responses. We then examined how inhibitory and excitatory synaptic input interacted with these intrinsic conductances to control DCN firing. We found that the output spiking of the model reflected the ongoing balance of excitatory and inhibitory input rates and that changing the level of inhibition performed an additive operation. Rebound firing following strong Purkinje cell input bursts was also possible, but only if the chloride reversal potential was more negative than −70 mV to allow de-inactivation of rebound currents. Fast rebound bursts due to T-type calcium current and slow rebounds due to persistent sodium current could be differentially regulated by synaptic input, and the pattern of these rebounds was further influenced by HCN current. Our findings suggest that active properties of DCN neurons could play a crucial role for signal processing in the cerebellum.     

Distribution and fate of DCX/PSA-NCAM expressing cells in the adult mammalian cortex: A local reservoir for adult cortical neuroplasticity?

The expression of early developmental markers such as doublecortin (DCX) and the polysialylated-neural cell adhesion molecule (PSA-NCAM) has been used to identify immature neurons within canonical neurogenic niches. Additionally, DCX/PSA-NCAM+ immature neurons reside in cortical layer II of the paleocortex and in the paleo- and entorhinal cortex of mice and rats, respectively. These cells are also found in the neocortex of guinea pigs, rabbits, some afrotherian mammals, cats, dogs, non-human primates, and humans. The population of cortical DCX/PSA-NCAM+ immature neurons is generated prenatally as conclusively demonstrated in mice, rats, and guinea pigs. Thus, the majority of these cells do not appear to be the product of adult proliferative events. The immature neurons in cortical layer II are most abundant in the cortices of young individuals, while very few DCX/PSA-NCAM + cortical neurons can be detected in aged mammals. Maturation of DCX/PSA-NCAM+ cells into glutamatergic and GABAergic neurons has been proposed as an explanation for the age-dependent reduction in their population over time. In this review, we compile the recent information regarding the age-related decrease in the number of cortical DCX/PSA-NCAM+ neurons. We compare the distribution and fates of DCX/PSA-NCAM + neurons among mammalian species and speculate their impact on cognitive function. To respond to the diversity of adult neurogenesis research produced over the last number of decades, we close this review by discussing the use and precision of the term “adult non-canonical neurogenesis.”     

Mechanisms of modification of excitatory and inhibitory inputs in various neurons of olivary-cerebellar network

It is known from the experimental data that at different cerebellar neurons there are voltage-dependent Ca2+ channels, NMDA receptors, metabotropic glutamate and GABAB receptors. This receptor arrangement ensures that activation of excitatory and inhibitory input results in changes in activity of protein kinases and phosphatases and subsequent modification of synaptic efficacy. The mechanism of synaptic plasticity is advanced that in accordance with the known experimental data concerning the modification of excitatory and inhibitory inputs to Purkinje cells, granule cells, and deep cerebellar nuclei cells. The mechanism is based on a postulate that phosphorylation/dephosphorylation of AMPA (GABAA) receptors on cerebellar cells causes the LTP/LTD of excitatory (LTD/LTP of inhibitory) transmission. It is assumed that modification rules for Purkinje cells, granule cells, and deep cerebellar nuclei cells, wherein cGMP-dependent protein kinase G is involved in synaptic plasticity, are distinct from those of hippocampal/neocortical cells, wherein cAMP-dependent protein kinase A is involved in synaptic plasticity, since cGMP (cAMP) concentration decreases (increases) with Ca2+ rise.     

Glutamate and Brain Glutaminases in Drug Addiction

Glutamate is the principal excitatory neurotransmitter in the central nervous system and its actions are related to the behavioral effects of psychostimulant drugs. In the last two decades, basic neuroscience research and preclinical studies with animal models are suggesting a critical role for glutamate transmission in drug reward, reinforcement, and relapse. Although most of the interest has been centered in post-synaptic glutamate receptors, the presynaptic synthesis of glutamate through brain glutaminases may also contribute to imbalances in glutamate homeostasis, a key feature of the glutamatergic hypothesis of addiction. Glutaminases are the main glutamate-producing enzymes in brain and dysregulation of their function have been associated with neurodegenerative diseases and neurological disorders; however, the possible implication of these enzymes in drug addiction remains largely unknown. This mini-review focuses on brain glutaminase isozymes and their alterations by in vivo exposure to drugs of abuse, which are discussed in the context of the glutamate homeostasis theory of addiction. Recent findings from mouse models have shown that drugs induce changes in the expression profiles of key glutamatergic transmission genes, although the molecular mechanisms that regulate drug-induced neuronal sensitization and behavioral plasticity are not clear.     

Maturation of membrane properties of neurons in the rat deep cerebellar nuclei

Patch clamp recordings of neurons in the adult rat deep cerebellar nuclei have been limited by the availability of viable brain slices. Using a new slicing technique, this study was designed to explore the maturation of membrane properties of neurons in the deep cerebellar nuclei (DCN)—an area involved in rat eyeblink conditioning. Compared to whole‐cell current–clamp recordings in DCN in rat pups at postnatal day 16 (P16) to P21, recordings from weanling rats at P22–P40 revealed a number of significant changes including an increase in the amplitude of the afterhyperpolarization (AHP)—an index of membrane excitability which has been shown to be important for eyeblink conditioning—a prolonged interval between the first and second evoked action potential, and an increase in AHP amplitude for hyperpolarization‐induced rebound spikes. This is the first report of developmental changes in membrane properties of DCN which may contribute to the ontogeny of eyeblink conditioning in the rat. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 74: 1268–1276, 2014