Biomedical subjects

Raphael Pinaud

Publications and source records attributed to Raphael Pinaud.

13 recordsLinked to original sources

PubMed2006

Presynaptic regulation of the inhibitory transmission by GluR5-containing kainate receptors in spinal substantia gelatinosa.

GluR5-containing kainate receptors (KARs) are known to be involved in nociceptive transmission. Our previous work has shown that the activation of presynaptic KARs regulates GABAergic and glycinergic synaptic transmission in cultured dorsal horn neurons. However, the role of GluR5-containing KARs in the modulation of inhibitory transmission in the spinal substantia gelatinosa (SG) in slices remains unknown. In the present study, pharmacological, electrophysiological and genetic methods were used to show that presynaptic GluR5 KARs are involved in the modulation of inhibitory transmission in the SG of spinal slices in vitro. The GluR5 selective agonist, ATPA, facilitated the frequency but not amplitude of spontaneous inhibitory postsynaptic currents (sIPSCs) in SG neurons. ATPA increased sIPSC frequency in all neurons with different firing patterns as delayed, tonic, initial and single spike patterns. The frequency of either GABAergic or glycinergic sIPSCs was significantly increased by ATPA. ATPA could also induce inward currents in all SG neurons recorded. The frequency, but not amplitude, of action potential-independent miniature IPSCs (mIPSCs) was also facilitated by ATPA in a concentration-dependent manner. However, the effect of ATPA on the frequency of either sIPSCs or mIPSCs was abolished in GluR5-/- mice. Deletion of the GluR5 subunit gene had no effect on the frequency or amplitude of mIPSCs in SG neurons. However, GluR5 antagonist LY293558 reversibly inhibited sIPSC and mIPSC frequencies in spinal SG neurons. Taken together, these results suggest that GluR5 KARs, which may be located at presynaptic terminals, contribute to the modulation of inhibitory transmission in the SG. GluR5-containing KARs are thus important for spinal sensory transmission/modulation in the spinal cord.

Action Potentials↗

PubMed2006

Calbindin-positive neurons reveal a sexual dimorphism within the songbird analogue of the mammalian auditory cortex.

The oscine song system, a set of interconnected brain nuclei involved in song production and learning, is one of the first and clearest examples of brain sexual dimorphism in a vertebrate, being typically well-developed in males, but not females. Here we present evidence for a sexual dimorphism in the caudomedial nidopallidum (NCM), an auditory area outside of the song system. NCM is thought to correspond to a portion of the auditory cortex of mammals and is involved in the perceptual processing of birdsong. We show that cells immunolabeled for the calcium-binding protein calbindin are primarily localized to caudal NCM and are almost twice as numerous in males as in females. We demonstrate that calbindin-positive cells constitute a subset of GABAergic cells in NCM, and show that the sex dimorphism in this cell population does not result from local gender differences in the overall density of neuronal or GABAergic cells. In addition, we demonstrate that calbindin-positive cells lack song-induced expression of the activity-dependent gene ZENK, and that song stimulation does not change the density or distribution of these cells in NCM. Finally, we show that the distribution of calbindin-positive cells in NCM is strikingly similar to the mRNA expression for the estrogen-generating enzyme aromatase. Together these results suggest that NCM is likely composed of neurochemically-distinct domains and presents a marked sex dimorphism in a specific subset of GABAergic neurons, which may confer sex-specific sensory processing capabilities to this auditory area. Our results also suggest that local sex steroid hormones may play a local role in auditory processing in the songbird telencephalon.

Animals↗

PubMed2006

Disparity for disinhibitory and excitatory effects during cortical reorganization.

Inhibitory and excitatory transmission have been shown to be two dominant forces in the process of injury-induced cortical reorganization. However, the contributions of each individual neurotransmitter system have been difficult to characterize, mainly because they often affect overlapping domains of the reorganizing cell's receptive field (RF). The present work differentiates the effects of either neurotransmitter system by studying reorganizing neurons where pharmacological intervention directed at glutamatergic or GABAergic networks affected spatially non-overlapping subfields within a cell's RF. Microiontophoresis was used to apply glutamate and bicuculline, a selective GABA-A receptor antagonist, to cells in the deafferented cortex at various post-amputation times, that ranged from 2 to 37 weeks. It was found that at all post-amputation times studied, glutamate increased the neural activity that could be evoked from mechanical stimulation over the wound area, in addition to decreasing the threshold for activation. Disinhibition with bicuculline application often lowered the response threshold for subfields within the reorganized RF, usually located on the digits, and could also expand RF area. Interestingly, the effects of GABAergic transmission to the process of reorganization appeared later than those mediated through glutamatergic networks. These findings suggest that recruitment of inhibition in reorganizing cells relies on activity-dependent mechanisms, with reinstatement of GABAergic transmission being secondary to the formation of novel glutamatergic drives.

Amputation, Surgical↗

PubMed2005

Presynaptic Na+ channels: locus, development, and recovery from inactivation at a high-fidelity synapse.

Na+ channel recovery from inactivation limits the maximal rate of neuronal firing. However, the properties of presynaptic Na+ channels are not well established because of the small size of most CNS boutons. Here we study the Na+ currents of the rat calyx of Held terminal and compare them with those of postsynaptic cells. We find that presynaptic Na+ currents recover from inactivation with a fast, single-exponential time constant (24 degrees C, tau of 1.4-1.8 ms; 35 degrees C, tau of 0.5 ms), and their inactivation rate accelerates twofold during development, which may contribute to the shortening of the action potential as the terminal matures. In contrast, recordings from postsynaptic cells in brainstem slices, and acutely dissociated, reveal that their Na+ currents recover from inactivation with a double-exponential time course (tau(fast) of 1.2-1.6 ms; tau(slow) of 80-125 ms; 24 degrees C). Surprisingly, confocal immunofluorescence revealed that Na+ channels are mostly absent from the calyx terminal but are instead highly concentrated in an unusually long (approximately 20-40 microm) unmyelinated axonal heminode. Outside-out patch recordings confirmed this segregation. Expression of Na(v)1.6 alpha-subunit increased during development, whereas the Na(v)1.2alpha-subunit was not present. Serial EM reconstructions also revealed a long pre-calyx heminode, and biophysical modeling showed that exclusion of Na+ channels from the calyx terminal produces an action potential waveform with a shorter half-width. We propose that the high density and polarized locus of Na+ channels on a long heminode are critical design features that allow the mature calyx of Held terminal to fire reliably at frequencies near 1 kHz.

Action Potentials↗

PubMed2005

Incongruent restoration of inhibitory transmission and general metabolic activity during reorganization of somatosensory cortex.

Activity markers cytochrome oxidase (CO) and glutamic acid decarboxylase (GAD) were analyzed in the primary somatosensory cortex of raccoons that underwent digit amputation. Subjects recovered for 2, 15, and 23 weeks following amputation of the fourth forepaw digit. Histochemistry was used to assess relative activity levels of both enzymes. We found a pronounced decrease in the numbers of CO intense patches in the cortical gyrus that had lost its original sensory input from the fourth digit. This decrease in CO activity was still apparent 15 weeks post-amputation. Conversely, no clear decrease in GAD levels could be identified in connection with the amputation procedure. Our findings present evidence that a significant decrease in metabolic activity results from the loss of the primary afferent sensory drive. The remaining GAD activity suggests that the absence of electrical activity, characteristic of reorganizing cortex, is likely to depend in part on lateral inhibitory cortical connections.

Afferent Pathways↗

PubMed2005

Co-induction of activity-dependent genes in songbirds.

Song behavior in songbirds induces the expression of activity-dependent genes in brain areas involved in perceptual processing, production and learning of song. This genomic response is thought to represent a link between neuronal activation and long-term changes in song-processing circuits of the songbird brain. Here we demonstrate that Arc, an activity-regulated gene whose product has dendritic localization and is associated with synaptic plasticity, is rapidly induced by song in the brain of zebra finches. We show that, in the context of song auditory stimulation, Arc expression is induced in several telencephalic auditory areas, most prominently the caudomedial nidopallium and mesopallium, whereas in the context of singing, Arc is also induced in song control areas, namely nucleus HVC, used as a proper name, the robust nucleus of the arcopallium and the interface nucleus of the nidopallium. We also show that song-induced Arc expression co-localizes at the cellular level with those of the transcriptional regulators zenk and c-fos, and that the song induction of these three genes is dependent on activation of the mitogen-activated protein kinase signaling pathway. These findings provide evidence for an involvement of Arc in the brain's response to birdsong. They also demonstrate that genes representing distinct genomic and cellular regulatory programs, namely early effectors and transcription factors, are co-activated in the same neuronal cells by a naturally learned stimulus.

Acoustic Stimulation↗

PubMed2004

Experience-dependent immediate early gene expression in the adult central nervous system: evidence from enriched-environment studies.

Here I discuss evidence from our group's work that implicates the immediate early genes NGFI-A and arc as possible regulators of neuronal plasticity. The enriched environment (EE) paradigm has been demonstrated to induce neural plasticity in both developing and mature mammals. Others and we have recently demonstrated that adult rats placed within an enriched environment underwent central nervous system-wide increases in the expression levels for the IEGs NGFI-A and arc. The relationships between the altered expression profiles for both genes in response to an EE exposure, and their putative role in orchestrating network restructuring in response to enhanced environmental complexity are discussed.

AIDS-Related Complex↗

PubMed2004

GABAergic neurons participate in the brain's response to birdsong auditory stimulation.

Birdsong is a learned vocal behaviour that requires intact hearing for its development in juveniles and for its maintenance during adulthood. However, the functional organization of the brain circuits involved in the perceptual processing of song has remained obscure. Here we provide evidence that GABAergic mechanisms are an important component of these circuits and participate in the auditory processing of birdsong. We first cloned a zebra finch homologue of the gene encoding the 65-kDa isoform of glutamic acid decarboxylase (zGAD-65), a specific GABAergic marker, and conducted an expression analysis by in situ hybridization to identify GABAergic cells and to map their distribution throughout auditory telencephalic areas. The results showed that field L2, the caudomedial nidopallium (NCM) and the caudomedial mesopallium (CMM) contain a high number of GABAergic cells. Using patch-clamp brain slice recordings, we found abundant GABAergic mIPSCs in NCM. Pharmacological antagonism of mIPSCs induced large EPSC bursts, suggesting that tonic inhibition helps to stabilize NCM against runaway excitation via activation of GABA-A receptors. Next, using double fluorescence in situ hybridization and double immunocytochemical labelling, we demonstrated that large numbers of GABAergic cells in NCM and CMM show inducible expression of the transcriptional regulator ZENK in response to song auditory stimulation. These data provide direct evidence that GABAergic neurons in auditory brain regions are activated by song stimulation. Altogether, our results suggest that GABAergic mechanisms participate in auditory processing and perception, and might contribute to the memorization of birdsong.

Acoustic Stimulation↗

PubMed2004

Song-induced gene expression: a window on song auditory processing and perception.

We review here evidence that a large portion of the caudomedial telencephalon of songbirds, distinct from the song control circuit, is involved in the perceptual processing of birdsong. When songbirds hear song, a number of caudomedial pallial areas are activated, as revealed by expression of the activity-dependent gene zenk. These areas, which include field L subfields L1 and L3, as well as the adjacent caudomedial nidopallium (NCM) and caudomedial mesopallium (CMM), are part of the central auditory pathway and constitute a lobule in the caudomedial aspect of the telencephalon. Several lines of evidence indicate that the neural circuits integrating this lobule are capable of performing the auditory processing of song based on fine acoustic features. Thus, this lobule is well positioned to mediate song perceptual processing and discrimination, which are required for vocal communication and vocal learning. Importantly, the zenk gene encodes a transcription factor linked to synaptic plasticity, and it regulates the expression of target genes associated with specific neuronal cell functions. The induction of zenk likely represents a key regulatory event in a gene cascade triggered by song and leading to neuronal plasticity. Thus, zenk may be linked to molecular and cellular mechanisms underlying experience-dependent modification of song-responsive circuits. In summary, songbirds possess an elaborate system for song perceptual processing and discrimination that potentially also subserves song-induced neuronal plasticity and song memory formation. The continued use of a multidisciplinary approach that integrates molecular, anatomical, physiological and behavioral methodologies has the potential to provide further significant insights into the underlying neurobiology of the perceptual aspects of vocal communication and learning.

Animals↗

PubMed2003

Light-induced Egr-1 expression in the striate cortex of the opossum.

In the present study, immunocytochemistry was used to assess the expression of Egr-1 nuclear protein across selected regions of the opossum visual system. In light-deprived (LD) animals, only a few scattered cell nuclei were found throughout the striate cortex (V1). Exposure to light promoted a significant increase in the density of Egr-1 labeled nuclei in V1. Laminar distribution of immunoreactive nuclei in light-stimulated animals (LS) tended to vary with topography: the lateral region, which corresponds to the central representation of the visual field, appeared to have higher density of cells expressing protein in the supragranular layers, as compared to the medial region, which corresponds to the representation of the peripheral field of vision. Finally, LS animals displayed a narrow band of labeled cell nuclei in the intergeniculate leaflet (IGL) and throughout the anteroposterior extent of the superior colliculus (SC). In contrast, almost no Egr-1 immunolabeling was found in the IGL and SC of LD animals. Our report is the first demonstration of light-regulated expression of the Egr-1 gene in the opossum visual system and provides evidence that the expression of an activity-dependent gene related to neural plasticity is evolutionarily conserved in the visual cortex of the mammalian lineage.

Animals↗

PubMed2003

Ngfi-a immunoreactivity in the primate retina: implications for genetic regulation of plasticity.

In rodents, enriched environments drive the expression of the immediate early gene NGFI-A, a regulator of the plasticity marker Synapsin I. Both proteins have been implicated as mediators of plasticity in the rat mammalian retina. In the present work immunocytochemistry directed against these proteins was used to explore their basal activity in the retina of a more visual species, the New World monkey Cebus apella. In contrast to rat, monkey retina displayed high basal expression of both NGFI-A and Synapsin I. The greatest number of NGFI-A -expressing cells was observed within the inner nuclear layer, although NGFI-A positive nuclei were also found in the ganglion cell layer. High levels of Synapsin I were found in the inner plexiform layer and outer plexiform layer. Our findings are consistent with the postulate that the retinas of highly visual animals may experience ongoing reorganization as part of normal visual processing, and that NGFI-A and Synapsin I may be well positioned to regulate some of these changes.

Animals↗

PubMed2002

Age-related distribution of c-fos expression in the striatum of CD-1 mice after acute methylphenidate administration.

Ritalin (methylphenidate hydrochloride, MPH) is the drug of choice for the treatment of attention deficit hyperactivity disorder. Previous research has shown that MPH administration affects the adult brain in a manner different from the young brain. In the current study, we set out to determine the target brain regions of acutely administered MPH at different stages of development. On postnatal days 3, 7, 11, 24, and 45, mice were treated with a single injection (s.c.) of saline, 5 or 20 mg/kg of MPH, and sacrificed 1 h later. Localization of c-fos expression was determined by immunocytochemistry. Compared to saline treated controls, mice treated with the high dose of MPH (20 mg/kg) showed dense Fos-immunoreactivity (Fos-IR) in the striatum. In most cases the low dose of MPH (5 mg/kg) produced only weak c-fos expression that was nearly indistinguishable from saline-treated controls. At PND 3 and 7, Fos-IR was localized in patches in the striatum. This patchy distribution of c-fos positive cells began to decline by PND 11 and was absent in PND 45 mice, with Fos-IR showing a scattered distribution throughout the striatum. The results of this study indicate that MPH induces the expression of c-fos in the same brain regions as cocaine and amphetamine, and that this expression is distributed differentially according to the age of the mouse.

Aging↗

PubMed2002

Plasticity-driven gene expression in the rat retina.

Animals exposed to an enriched environment display features of neural plasticity such as an increased brain volume, enhanced number of dendritic spines, as well as enlarged synapses. Here we report the first description of molecular plasticity in the mammalian retina, as revealed by gene expression. A marked upregulation of both NGFI-A and Arc, two candidate-plasticity genes, was observed in adult rats that had been exposed to an enriched environment for 3 weeks. This increase was paralleled by an increase in the expression of the late genes GAP-43 and Synapsin I, which also indicated changes in retinal connectivity. Our results suggest that both NGFI-A and Arc may regulate mechanisms of plasticity that had been invoked by heightened complexity of the visual environment.

Animals↗