AB1570 Sigma-AldrichAnti-GABA Transporter-1 Antibody, CT (a.a. 588-599)

Studies in rodents revealed that selective accumulation of Na(+) channel subtypes at the axon initial segment (AIS) determines action potential (AP) initiation and backpropagation in cortical pyramidal cells (PCs); however, in human cortex, the molecular identity of Na(+) channels distributed at PC axons, including the AIS and the nodes of Ranvier, remains unclear. We performed immunostaining experiments in human cortical tissues removed surgically to cure brain diseases. We found strong immunosignals of Na(+) channels and two channel subtypes, NaV1.2 and NaV1.6, at the AIS of human cortical PCs. Although both channel subtypes were expressed along the entire AIS, the peak immunosignals of NaV1.2 and NaV1.6 were found at proximal and distal AIS regions, respectively. Surprisingly, in addition to the presence of NaV1.6 at the nodes of Ranvier, NaV1.2 was also found in a subpopulation of nodes in the adult human cortex, different from the absence of NaV1.2 in myelinated axons in rodents. NaV1.1 immunosignals were not detected at either the AIS or the nodes of Ranvier of PCs; however, they were expressed at interneuron axons with different distribution patterns. Further experiments revealed that parvalbumin-positive GABAergic axon cartridges selectively innervated distal AIS regions with relatively high immunosignals of NaV1.6 but not the proximal NaV1.2-enriched compartments, suggesting an important role of axo-axonic cells in regulating AP initiation in human PCs. Together, our results show that both NaV1.2 and NaV1.6 (but not NaV1.1) channel subtypes are expressed at the AIS and the nodes of Ranvier in adult human cortical PCs, suggesting that these channel subtypes control neuronal excitability and signal conduction in PC axons.

Analgesia is a well-documented effect of acupuncture. A critical role in pain sensation plays the nervous system, including the GABAergic system and opioid receptor (OR) activation. Here we investigated regulation of GABA transporter GAT1 by δOR in rats and in Xenopus oocytes. Synaptosomes of brain from rats chronically exposed to opiates exhibited reduced GABA uptake, indicating that GABA transport might be regulated by opioid receptors. For further investigation we have expressed GAT1 of mouse brain together with mouse δOR and μOR in Xenopus oocytes. The function of GAT1 was analyzed in terms of Na(+)-dependent [(3)H]GABA uptake as well as GAT1-mediated currents. Coexpression of δOR led to reduced number of fully functional GAT1 transporters, reduced substrate translocation, and GAT1-mediated current. Activation of δOR further reduced the rate of GABA uptake as well as GAT1-mediated current. Coexpression of μOR, as well as μOR activation, affected neither the number of transporters, nor rate of GABA uptake, nor GAT1-mediated current. Inhibition of GAT1-mediated current by activation of δOR was confirmed in whole-cell patch-clamp experiments on rat brain slices of periaqueductal gray. We conclude that inhibition of GAT1 function will strengthen the inhibitory action of the GABAergic system and hence may contribute to acupuncture-induced analgesia.

The serotonergic (5-HTergic) system arising from the dorsal raphe nucleus (DRN) is implicated in various physiological and behavioral processes, including stress responses. The DRN is comprised of several subnuclei, serving specific functions with distinct afferent and efferent connections. Furthermore, subsets of 5-HTergic neurons are known to coexpress other transmitters, including GABA, glutamate, or neuropeptides, thereby generating further heterogeneity. However, despite the growing evidence for functional variations among DRN subnuclei, relatively little is known about how they map onto neurochemical diversity of 5-HTergic neurons. In the present study, we characterized functional properties of GAD67-expressing 5-HTergic neurons (5-HT/GAD67 neurons) in the rat DRN, and compared with those of neurons expressing 5-HTergic molecules (5-HT neurons) or GAD67 alone. While 5-HT/GAD67 neurons were absent in the dorsomedial (DRD) or ventromedial (DRV) parts of the DRN, they were selectively distributed in the lateral wing of the DRN (DRL), constituting 12% of the total DRL neurons. They expressed plasmalemmal GABA transporter 1, but lacked vesicular inhibitory amino acid transporter. By using whole-cell patch-clamp recording, we found that 5-HT/GAD67 neurons had lower input resistance and firing frequency than 5-HT neurons. As revealed by c-Fos immunohistochemistry, neurons in the DRL, particularly 5-HT/GAD67 neurons, showed higher responsiveness to exposure to an open field arena than those in the DRD and DRV. By contrast, exposure to contextual fear conditioning stress showed no such regional differences. These findings indicate that 5-HT/GAD67 neurons constitute a unique neuronal population with distinctive neurochemical and electrophysiological properties and high responsiveness to innocuous stressor.

During brain development, the neocortex shows periods of enhanced plasticity, which enables the acquisition of knowledge and skills that we use and build on in adult life. Key to persistent modifications of neuronal connectivity and plasticity of the neocortex are molecular changes occurring at the synapse. Here we used isobaric tag for relative and absolute quantification to measure levels of 467 synaptic proteins in a well-established model of plasticity in the mouse visual cortex and the regulation of its critical period. We found that inducing visual cortex plasticity by monocular deprivation during the critical period increased levels of kinases and proteins regulating the actin-cytoskeleton and endocytosis. Upon closure of the critical period with age, proteins associated with transmitter vesicle release and the tubulin- and septin-cytoskeletons increased, whereas actin-regulators decreased in line with augmented synapse stability and efficacy. Maintaining the visual cortex in a plastic state by dark rearing mice into adulthood only partially prevented these changes and increased levels of G-proteins and protein kinase A subunits. This suggests that in contrast to the general belief, dark rearing does not simply delay cortical development but may activate signaling pathways that specifically maintain or increase the plasticity potential of the visual cortex. Altogether, this study identified many novel candidate plasticity proteins and signaling pathways that mediate synaptic plasticity during critical developmental periods or restrict it in adulthood.

The neurons in the cortical white matter (WM neurons) originate from the first set of postmitotic neurons that migrates from the ventricular zone. In particular, they arise in the subplate that contains the earliest cells generated in the telencephalon, prior to the appearance of neurons in gray matter cortical layers. These cortical WM neurons are very numerous during development, when they are thought to participate in transient synaptic networks, although many of these cells later die, and relatively few cells survive as WM neurons in the adult. We used light and electron microscopy to analyze the distribution and density of WM neurons in various areas of the adult human cerebral cortex. Furthermore, we examined the perisomatic innervation of these neurons and estimated the density of synapses in the white matter. Finally, we examined the distribution and neurochemical nature of interneurons that putatively innervate the somata of WM neurons. From the data obtained, we can draw three main conclusions: first, the density of WM neurons varies depending on the cortical areas; second, calretinin-immunoreactive neurons represent the major subpopulation of GABAergic WM neurons; and, third, the somata of WM neurons are surrounded by both glutamatergic and GABAergic axon terminals, although only symmetric axosomatic synapses were found. By contrast, both symmetric and asymmetric axodendritic synapses were observed in the neuropil. We discuss the possible functional implications of these findings in terms of cortical circuits.

Neurofibrillary tangles (NFT) represent one of the main neuropathological features in the cerebral cortex associated with Alzheimer's disease (AD). This neurofibrillary lesion involves the accumulation of abnormally hyperphosphorylated or abnormally phosphorylated microtubule-associated protein tau into paired helical filaments (PHF-tau) within neurons. We have used immunocytochemical techniques and confocal microscopy reconstructions to examine the distribution of PHF-tau-immunoreactive (ir) cells, and their perisomatic GABAergic and glutamatergic innervations in the hippocampal formation and adjacent cortex of AD patients. Furthermore, correlative light and electron microscopy was employed to examine these neurons and the perisomatic synapses. We observed two patterns of staining in PHF-tau-ir neurons, pattern I (without NFT) and pattern II (with NFT), the distribution of which varies according to the cortical layer and area. Furthermore, the distribution of both GABAergic and glutamatergic terminals around the soma and proximal processes of PHF-tau-ir neurons does not seem to be altered as it is indistinguishable from both control cases and from adjacent neurons that did not contain PHF-tau. At the electron microscope level, a normal looking neuropil with typical symmetric and asymmetric synapses was observed around PHF-tau-ir neurons. These observations suggest that the synaptic connectivity around the perisomatic region of these PHF-tau-ir neurons was apparently unaltered.

The GABA transporters GAT-1 and GAT-3 are abundant in the external and internal segments of the globus pallidus (GPe and GPi, respectively). We have shown that pharmacological blockade of either of these transporters results in decreased neuronal firing, and in elevated levels of extracellular GABA in normal monkeys. We now studied whether the electrophysiologic and biochemical effects of local intra-pallidal injections of GAT-1 and GAT-3 blockers, or the subcellular localization of these transporters, are altered in monkeys rendered parkinsonian by the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The subcellular localization of the transporters in GPe and GPi, studied with electron microscopy immunoperoxidase, was similar to that found in normal animals: i.e., GAT-3 immunoreactivity was mostly confined to glial processes, while GAT-1 labeling was expressed in unmyelinated axons and glial processes. A combined injection/recording device was used to record the extracellular activity of single neurons in GPe and GPi, before, during and after administration of small volumes (1microl) of either the GAT-1 inhibitor, SKF-89976A hydrochloride (720ng), or the GAT-3 inhibitor, (S)-SNAP-5114 (500ng). In GPe, the effects of GAT-1 or GAT-3 blockade were similar to those seen in normal monkeys. However, unlike the findings in the normal state, the firing of most neurons was not affected by blockade of either transporter in GPi. These results suggest that, after dopaminergic depletion, the functions of GABA transporters are altered in GPi; without major changes in their subcellular localization.

Glutamate (Glu) and gamma-aminobutyric acid (GABA) transporters play important roles in regulating neuronal activity. Glu is removed from the extracellular space dominantly by glial transporters. In contrast, GABA is mainly taken up by neurons. However, the glial GABA transporter subtypes share their localization with the Glu transporters and their expression is confined to the same subpopulation of astrocytes, raising the possibility of cooperation between Glu and GABA transport processes.Here we used diverse biological models both in vitro and in vivo to explore the interplay between these processes. We found that removal of Glu by astrocytic transporters triggers an elevation in the extracellular level of GABA. This coupling between excitatory and inhibitory signaling was found to be independent of Glu receptor-mediated depolarization, external presence of Ca(2+) and glutamate decarboxylase activity. It was abolished in the presence of non-transportable blockers of glial Glu or GABA transporters, suggesting that the concerted action of these transporters underlies the process.Our results suggest that activation of Glu transporters results in GABA release through reversal of glial GABA transporters. This transporter-mediated interplay represents a direct link between inhibitory and excitatory neurotransmission and may function as a negative feedback combating intense excitation in pathological conditions such as epilepsy or ischemia.

Mammalian retinas comprise an enormous variety of amacrine cells with distinct properties and functions. The present paper describes a new interplexiform amacrine cell type in the mouse retina. A transgenic mouse mutant was used that expressed the gene for the enhanced green fluorescent protein (EGFP) instead of the coding DNA of connexin45 in several retinal cell classes, among which a single amacrine cell population was most prominently labelled. Staining for EGFP and different marker proteins showed that these amacrine cells are interplexiform: they stratify in stratum S4/5 of the inner plexiform layer and send processes to the outer plexiform layer. These cells were termed IPA-S4/5 cells. They belong to the group of medium-field amacrine cells and are coupled homologously and heterologously to other amacrine cells by connexin45. Immunostaining revealed that IPA-S4/5 cells are GABAergic and express GAT-1, a plasma-membrane-bound GABA transporter possibly involved in non-vesicular GABA release. To characterize the light responses of IPA-S4/5 cells, patch-clamp recordings in retinal slices were made. Consistent with their stratification in the ON sublamina of the inner plexiform layer, cells depolarized in response to light ON stimuli and transiently hyperpolarized in response to light OFF. Responses of cells to green (578 nm) and blue (400 nm) light suggest that they receive input from cone bipolar cells contacting both M- and S-cones, possibly with reduced S-cone input. A new type of interplexiform ON amacrine cell is described, which is strongly coupled and uses GABA but not dopamine as its neurotransmitter.

A number of human brain diseases have been associated with disturbances in the structure and function of cortical synapses. Answering fundamental questions about the synaptic machinery in these disease states requires the ability to image and quantify small synaptic structures in tissue sections and to evaluate protein levels at these major sites of function. We developed a new automated segmentation imaging method specifically to answer such fundamental questions. The method takes advantage of advances in spinning disk confocal microscopy, and combines information from multiple iterations of a fluorescence intensity/morphological segmentation protocol to construct three-dimensional object masks of immunoreactive (IR) puncta. This new methodology is unique in that high- and low-fluorescing IR puncta are equally masked, allowing for quantification of the number of fluorescently-labeled puncta in tissue sections. In addition, the shape of the final object masks highly represents their corresponding original data. Thus, the object masks can be used to extract information about the IR puncta (e.g., average fluorescence intensity of proteins of interest). Importantly, the segmentation method presented can be easily adapted for use with most existing microscopy analysis packages.