Neuronal and glial localization of GABA transporter immunoreactivity in the myenteric plexus

Abstract

The neurotransmitter gamma-aminobutyric acid (GABA) is removed from the extracellular space by sodium and chloride dependent high affinity plasma membrane transporters. In the rat central nervous system, three GABA transporters, GAT1, GAT2 and GAT3, have been cloned and localized by immunohistochemistry. The purpose of this study was to examine the distribution of these transporters within the myenteric plexus of the rat gastrointestinal tract. We investigated their cellular locations using GAT1-3 specific antisera in lightly fixed segments of rat duodenum, ileum and colon. Immunohistochemistry revealed a large number of GAT2-immunoreactive structures that surrounded neurons within each ganglion of the myenteric plexus. GAT2 was colocalized in these structures with the glial cell marker p75(NTR), suggesting that the predominant high affinity GABA transporter within enteric glia is GAT2. GAT3 immunoreactivity was localized within many nerve cell bodies, and no labeling for GAT1 was detected, although it was present in retina, which was used as a control. Double labeling for calretinin and nitric oxide synthase (NOS) revealed colocalization of GAT3 with approximately 75% of calretinin-immunoreactive neurons and 15% of NOS-immunoreactive neurons. This suggests that a small proportion of inhibitory motor neurons and at least some putative intrinsic primary afferent neurons within the rat gastrointestinal tract express GAT3. Thus NOS neurons, which appear to utilize GABA as a transmitter, and calretinin-immunoreactive neurons, which do not appear to be GABAergic, both express immunoreactivity for GABA transporters.

Glutamate- and GABA-mediated neuron–satellite cell interaction in nodose ganglia as revealed by intracellular calcium imaging

“…It is known that there is a characteristic distribution of GABA transporters across different regions. In the myenteric plexus, it was reported that GAT-2 is expressed in glial cells and GAT-3 is expressed in neurons (Fletcher et al 2002). In the central nervous system, GAT-1 and GAT-3 are expressed abundantly, and GAT-1 is expressed in neurons and, to some degree, in astrocytes, whereas GAT-3 is the predominant GABA transporter within astrocytes (Barbaresi et al 2001;Minelli et al 1996).…”

Expression of a functional metabotropic glutamate receptor 5 on enteric glia is altered in states of inflammation

“…Indeed, enteric glia release neurotransmitters in vitro (Zhang et al, 2003), express receptors (Kimball and Mulholland, 1996;Nasser et al, 2006b;Van Nassauw et al, 2006;Vanderwinden et al, 2003;von Boyen et al, 2006), biosynthetic enzymes (Jessen and Mirsky, 1983) as well as reuptake transporters (Fletcher et al, 2002;Ruhl et al, 2005) for neurotransmitters. Functional disruption of enteric glia causes subtle changes in intestinal motility (Aube, 2005;Nasser et al, 2006a), suggesting that these cells modulate enteric neural signaling.…”

Clostridium difficile-related postinfectious IBS: a case of enteroglial microbiological stalking and/or the solution of a conundrum?

“…Most EGC within enteric ganglia are contacted by vesiculated nerve processes with presynaptic specializations [35], and respond to transmitters released by these terminations by expressing a series of receptors for neurotransmitters and neuromodulators [36][37][38][39]. Thus, EGC can modulate enteric neural circuits in several ways, such as by supplying neurotransmitters precursors to neurons [40,41], terminating the actions of neurotransmitters from synapses [42,43], and through the generation of neuroactive compounds [44]. In addition, EGC are needed to assure survival of the enteric neurons, as demonstrated by the experimental ablation of the intestinal glial network [45].…”