Expression of alpha3, beta3 and gamma1 GABA(A) receptor subunit messenger RNAs in visual cortex and lateral geniculate nucleus of normal and monocularly deprived monkeys

Targeted disruption of layer 4 during development increases GABAA receptor neurotransmission in the neocortex

Cortical dysplasia (CD) associates with clinical pathologies, including epilepsy and mental retardation. CD results from impaired migration of immature neurons to their cortical targets, leading to clustering of neural cells and changes in cortical properties. We developed a CD model by administering methylazoxymethanol (MAM), an anti-mitotic, to pregnant ferrets on embryonic day 33; this leads to reduction in cortical thickness in addition to redistribution and increased expression of GABAA receptors (GABAAR). We evaluated the impact of MAM treatment on GABAAR-mediated synaptic transmission in postnatal day 0-1 neurons, leaving the ganglionic eminence (GE) and in layer 2/3 pyramidal cells of postnatal day 28-38 ferrets. Embryonic day 33 MAM treatment significantly increases the amplitude and frequency of spontaneous GABAAR-mediated inhibitory postsynaptic currents (IPSCs) in the cells leaving the GE. In older MAM-treated animals, the amplitude and frequency of GABAAR-mediated spontaneous IPSCs in layer 2/3 pyramidal cells is increased, as are the amplitude and frequency of miniature IPSCs. The kinetics of GABAAR opening also altered following treatment with MAM. Western blot analysis shows that the expression of the GABAAα3R and GABAAγ2R subunits amplified in our model animals. We did not observe any significant change in the passive properties of either the layer 2/3 pyramidal cells or cells leaving the GE after MAM treatment. These observations reinforce the idea that synaptic neurotransmission through GABAAR enhances following treatment with MAM and coincides with our finding of increased GABAAαR expression within the upper cortical layers. Overall, we demonstrate that small amounts of toxins delivered during corticogenesis can result in long-lasting changes in ambient expression of GABAAR that influence intrinsic neuronal properties.

Differential expression patterns of OCC1-related, extracellular matrix proteins in the lateral geniculate nucleus of macaque monkeys

The extracellular matrix (ECM) plays important roles in the development and plasticity of the central nervous system, and it has been shown that it regulates reorganization of the neuronal network. We have found that expression of OCC1, testican-1, testican-2, testican-3, SPARC and SC1 mRNAs, which encode members of the OCC1-related family of ECM proteins, exhibits distinct activity-dependent expression patterns in the adult macaque visual cortex. This finding suggests that OCC1-related proteins play crucial roles in the visual processing pathway. In the present study, we examined mRNA expression patterns of OCC1-related genes in the dorsal lateral geniculate nucleus (dLGN) of macaques. The mRNAs of testican-1 and testican-2 were strongly expressed in both excitatory projection neurons and GABAergic interneurons in the dLGN. Expression of testican-3 mRNA, which is predominantly observed in GABAergic interneurons in the cortex, was restricted to excitatory projection neurons in the dLGN. SPARC mRNA was strongly, and exclusively, expressed in glial cells in the dLGN. Interestingly, neuronal SC1 mRNA expression was abundantly observed in intercalated, koniocellular layers of the dLGN, while it was preferentially observed in blob regions of the primary visual area that receives color coding K-pathway projection from dLGN koniocellular layers, suggesting a pathway preference of expression. Finally, monocular inactivation experiments demonstrated that expression of testican-1, testican-2 and testican-3 mRNAs in the dLGN is dependent on sensory activity. Given their differential expression patterns and activity dependence, products of OCC1-related genes may modulate visual processing and plasticity at the level of the dLGN and the visual cortex.

Reticular nucleus-specific changes in alpha3 subunit protein at GABA synapses in genetically epilepsy-prone rats

Differential composition of GABA(A) receptor (GABA(A)R) subunits underlies the variability of fast inhibitory synaptic transmission; alteration of specific GABA(A)R subunits in localized brain regions may contribute to abnormal brain states such as absence epilepsy. We combined immunocytochemistry and high-resolution ImmunoGold electron microscopy to study cellular and subcellular localization of GABA(A)R alpha1, alpha3, and beta2/beta3 subunits in ventral posterior nucleus (VP) and reticular nucleus (RTN) of control rats and WAG/Rij rats, a genetic model of absence epilepsy. In control rats, alpha1 subunits were prominent at inhibitory synapses in VP and much less prominent in RTN; in contrast, the alpha3 subunit was highly evident at inhibitory synapses in RTN. beta2/beta3 subunits were evenly distributed at inhibitory synapses in both VP and RTN. ImmunoGold particles representing all subunits were concentrated at postsynaptic densities with no extrasynaptic localization. Calculated mean number of particles for alpha1 subunit per postsynaptic density in nonepileptic VP was 6.1 +/- 3.7, for alpha3 subunit in RTN it was 6.6 +/- 3.4, and for beta2/beta3 subunits in VP and RTN the mean numbers were 3.7 +/- 1.3 and 3.5 +/- 1.2, respectively. In WAG/Rij rats, there was a specific loss of alpha3 subunit immunoreactivity at inhibitory synapses in RTN, without reduction in alpha3 subunit mRNA or significant change in immunostaining for other markers of RTN cell identity such as GABA or parvalbumin. alpha3 immunostaining in cortex was unchanged. Subtle, localized changes in GABA(A)R expression acting at highly specific points in the interconnected thalamocortical network lie at the heart of idiopathic generalized epilepsy.

Modulation of GABA receptor subunits in rat facial motoneurons after axotomy

Facial nerve axotomy is a good model for studying neuronal plasticity and regeneration in the peripheral nervous system. In the present study, we investigated the effect of axotomy on the different subunits of GABA(A) and GABA(B) receptors of facial motoneurons. The facial nerve trunk was unilaterally sectioned and operated rats were sacrificed at 1, 3, 8, 30, and 60 days later. mRNAs coding for alpha1, beta2, and gamma2 of GABA(A) receptors and for GABA(1B) and GABA(B2) receptors were down-regulated by axotomy. This decrease began as soon as 1 or 3 days after axotomy, and the minimum was 8 days post-lesion; the mRNA levels remained lower than normal at day post-lesion 60. The abundance of mRNAs coding for the three other alpha2, beta1, and beta3 facial subunits of GABA(A) receptors and for the pre-synaptic GABA(B1A) subunit remained unchanged during the period 1-8 days post-lesion. Immunohistochemistry using specific antibodies against alpha1, gamma2 subunits of GABA(A) and against GABA(B2) subunits confirmed this down-regulation. Colchicine treatment and blockade of action potential by tetrodotoxin significantly decreased GABA(A)alpha1 immunoreactivity in the axotomized facial nucleus after 7 days. Finally, muscle destruction by cardiotoxin or facial palsy induced by botulinum toxin failed to change GABA(A)alpha1 subunit expression. Our data demonstrate that axotomy strongly reduced the amounts of alpha1, beta2, and gamma2 subunits of GABA(A) receptors and B(1B) and B(2) subunits of GABA(B) receptors in the axotomized facial motoneurons. The loss of GABA(A)alpha1 subunit was most probably induced by both the loss of trophic factors transported from the periphery and a positive injury signal. It also seems to be dependent on activity disruption.

An in situ hybridization and immunofluorescence study of GABAA and GABAB receptors in the vestibular nuclei of the intact and unilaterally labyrinthectomized rat

We investigated whether the production of the sixteen subunits of the GABA(A) receptors and of the different variants of GABA Breceptors are modulated in rat medial vestibular nuclei (MVN) following unilateral labyrinthectomy. Specific alpha1-6, beta1-3, gamma1-3 and delta GABA(A) and GABA(B) B1 and B2receptor radioactive oligonucleotides were used for in situ hybridization to probe sections of rat vestibular nuclei. Specific antibodies against alpha1, beta2, beta3 and gamma2 subunits of GABA(A) receptors and against GABA( B)receptors were also used to detect a potential protein expression modulation. No asymmetry was observed by autoradiography in the intact and deafferented MVN at any time (5 h to 8 days) following the lesion and for any of the oligonucleotide probes used. Also, no difference in the alpha1, beta2, beta3 and gamma2 of the GABA(A) and in the GABA(B) receptor immunohistochemical signal could be detected between the intact and deafferented vestibular nuclei at any time following the lesion. Our data suggest that GABA(A) and GABA Breceptor density changes most probably were not involved in the early stage of the vestibular compensation process, i.e., in the restoration of a normal resting discharge of the deafferented vestibular neurons and consequently in the recovery of a normal posture and eye position.

Adaptive responses of monkey somatosensory cortex to peripheral and central deafferentation

This study deals with two kinds of activity-dependent phenomena in the somatosensory cortex of adult monkeys, both of which may be related: (1) mutability of representational maps, as defined electrophysiologically; (2) alterations in expression of genes important in the inhibitory and excitatory neurotransmitter systems. Area 3b of the cerebral cortex was mapped physiologically and mRNA levels or numbers of immunocytochemically stained neurons quantified after disrupting afferent input peripherally by section of peripheral nerves, or centrally by making lesions of increasing size in the somatosensory thalamus. Survival times ranged from a few weeks to many months. Mapping studies after peripheral nerve lesions replicated results of previous studies in showing the contraction of representations deprived of sensory input and expansion of adjacent representations. However, these changes in representational maps were in most cases unaccompanied by significant alterations in gene expression for calcium calmodulin-dependent protein kinase isoforms, for glutamic acid decarboxylase, GABA(A) receptor subunits, GABA(B) receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) or N-methyl-D-aspartate (NMDA) receptor subunits. Mapping studies after lesions in the ventral posterior lateral nucleus (VPL) of the thalamus revealed no changes in cortical representations of the hand or fingers until >15% of the thalamic representation was destroyed, and only slight changes until approximately 45% of the representation was destroyed, at which point the cortical representation of the finger at the center of a lesion began to shrink. Lesions destroying >60% of VPL resulted in silencing of the hand representation. Although all lesions were associated with a loss of parvalbumin-immunoreactive thalamocortical fiber terminations, and of cytochrome oxidase staining in a focal zone of area 3b, no changes in gene expression could be detected in the affected zone until >40-50% of VPL was destroyed, and even after that changes in mRNA levels or in numbers of GABA-immunoreactive neurons in the affected zone were remarkably small. The results of these studies differ markedly from the robust changes in gene expression detectable in the visual cortex of monkeys deprived of vision in one eye. The results confirm the view that divergence of the afferent somatosensory pathways from periphery to cerebral cortex is sufficiently great that many fibers can be lost before neuronal activity is totally silenced in area 3b. This divergence is capable of maintaining a high degree of cortical function in the face of diminishing inputs from the periphery and is probably an important element in promoting representational plasticity in response to altered patterns of afferent input.

Gene expression in the brain across the sleep-waking cycle

Sleep and waking differ significantly in terms of behavior, metabolism, and neuronal activity. Recent evidence indicates that sleep and waking also differ with respect to the expression of certain genes. To systematically investigate such changes, we used mRNA differential display and cDNA microarrays to screen approximately 10000 transcripts expressed in the cerebral cortex of rats after 8 h of sleep, spontaneous waking, or sleep deprivation. We found that 44 genes had higher mRNA levels after waking and/or sleep deprivation relative to sleep, while 10 were upregulated after sleep. Known genes that were upregulated in waking and sleep deprivation can be grouped into the following categories: immediate early genes/transcription factors (Arc, CHOP, IER5, NGFI-A, NGFI-B, N-Ras, Stat3), genes related to energy metabolism (glucose type I transporter Glut1, Vgf), growth factors/adhesion molecules (BDNF, TrkB, F3 adhesion molecule), chaperones/heat shock proteins (BiP, ERP72, GRP75, HSP60, HSP70), vesicle- and synapse-related genes (chromogranin C, synaptotagmin IV), neurotransmitter/hormone receptors (adrenergic receptor alpha(1A) and beta(2), GABA(A) receptor beta(3), glutamate NMDA receptor 2A, glutamate AMPA receptor GluR2 and GluR3, nicotinic acetylcholine receptor beta(2), thyroid hormone receptor TRbeta), neurotransmitter transporters (glutamate/aspartate transporter GLAST, Na(+)/Cl(-) transporter NTT4/Rxt1), enzymes (aryl sulfotransferase, c-jun N-terminal kinase 1, serum/glucocorticoid-induced serine/threonine kinase), and a miscellaneous group (calmodulin, cyclin D2, LMO-4, metallothionein 3). Several other genes that were upregulated in waking and all the genes upregulated in sleep, with the exception of the one coding for membrane protein E25, did not match any known sequence. Thus, significant changes in gene expression occur across behavioral states, which are likely to affect basic cellular functions such as RNA and protein synthesis, neural plasticity, neurotransmission, and metabolism.

The mouse GABA(A) receptor alpha3 subunit gene and promoter

Gamma-aminobutyric acid (GABA) type A receptors are multisubunit ligand-gated ion channels which mediate inhibition in the brain. The GABA(A) receptor alpha3 subunit gene exhibits extensive variation in its developmental and regional expression, but the detailed mechanisms governing the expression patterns of this gene remain unknown. We have cloned and begun to characterize the murine alpha3 subunit gene Gabra3. All but one of the 10 exons and the intron-exon boundaries have been sequenced; the first intron is in the 5' untranslated region (5'UTR) of the alpha3 mRNA. Rapid amplification of the cDNA 5'-end (5'-RACE) and RNase protection indicated many transcription start sites, with the major site (=+1) corresponding to a 5'UTR of 178 bases. Most sites were in or just downstream of a region of 55 (mouse) and 25 (human) GA repeats in the proximal promoter, as revealed by genome walking of Gabra3 and the human gene GABRA3. No canonical TATA or CAAT boxes or initiator (Inr) sites were found in either promoter, but both contained conserved consensus sites for several transcription factors. Progressive deletion of the mouse promoter produced positive or negative effects on expression of reporter (luciferase) constructs, with the highest observed activity in several types of transiently transfected cells for a construct containing bases -320 to +35. The GA repeats and a much shorter nearby series of four GC repeats, the first three of which are part of a consensus E2F site, appear to contribute significantly to mouse promoter activity. Upstream GA repeats enhanced activity of the SV40 promoter, and the GA repeat sequence bound nuclear proteins from several tissues.

Temporal modulation of GABA(A) receptor subunit gene expression in developing monkey cerebral cortex

In situ hybridization histochemistry was used to examine the expression of 10 GABA(A) receptor messenger RNAs corresponding to the alpha1-alpha5, beta1-beta3, gamma1 and gamma2 subunits in primary somatosensory and visual areas of macaque monkey cerebral cortex from embryonic day (E) 125 to postnatal day (P) 125. Results were compared with expression patterns in adults. In the sensorimotor cortex at E125, overall levels of all subunit transcripts were low. At E137, there was a major lamina-specific increase in all subunit messenger RNAs except gamma1. For alpha1, alpha2, alpha4, beta2, beta3 and gamma2 subunit transcripts, this increase was highest in areas 3a and 3b, particularly in layers III/IV and VI. Postnatally, there were significant decreases in all transcripts. Alpha1, alpha5, beta2 and gamma2 subunit transcripts, while still at significantly lower levels than at E137, remained expressed at levels higher than other transcripts. Unlike in rodents, there was no obvious "switch" in the major subunits expressed in fetal and adult cortex, alpha1, alpha5, beta2 and gamma2 remaining highest throughout. In area 17, the most prominently expressed subunits at earliest ages were alpha2, alpha5, beta1, beta2, beta3 and gamma2, especially in layers II/III and VI. At E150, expression for alpha2, alpha3, beta1 and beta3 subunit transcripts in these layers decreased, but levels for alpha1, alpha4, alpha5, beta2, gamma1 and gamma2 transcripts increased, particularly within layer IV. The increase at E150 was particularly marked for alpha5 transcripts, which were expressed at levels more than four times those of other transcripts. Alpha1, beta2 and gamma2 remain highest into aduthood. Fetal area 17 displayed lamina-specific patterns of expression not found in adult animals. In particular, alpha3 messenger RNAs were present in layer IVA and gamma1 transcripts were present in layer IVC at E150, despite a lack of expression in these layers in the adult. These data demonstrate increased expression of GABA(A) receptors during the period of establishment of thalamocortical and intracortical connections, and a temporal regulation that may be associated with the period of developmental plasticity.