Postsynaptic localization of γ‐aminobutyric acid transporters and receptors in the outer plexiform layer of the goldfish retina: An ultrastructural study

Abstract

The gamma-aminobutyric acid (GABA)-ergic system in the outer plexiform layer (OPL) of the goldfish retina was studied via light and electron immunohistochemistry. The subcellular distributions of immunoreactivity (-IR) of plasma membrane GABA transporters GAT2 and GAT3, the alpha1 and alpha3 subunits of the ionotropic GABA(A) receptor, and the rho1 subunit of the ionotropic GABA(C) receptor were determined. The localization of the GAT2-IR and GAT3-IR to horizontal cell dendrites at the base of the cone synaptic complex was the main characteristic at the ultrastructural level. Very rarely, GAT2-IR and GAT3-IR were found in horizontal cell dendrites innervating rod spherules. alpha1-IR and alpha3-IR were seen in wide bands in the OPL, whereas rho1-IR appeared as a narrow band in the OPL. Most alpha1-IR was intracellular in rod and cone terminals. Membrane-associated alpha1-IR was observed in cone pedicles but not in rod spherules; postsynaptic elements were also labeled. alpha3-IR was concentrated in the lateral elements of horizontal cell dendrites in cone pedicles. In contrast, rho1-IR was found mainly on the spinules of the horizontal cell dendrites in cone pedicles. In addition, in another type of cone pedicle, rho1-IR was found at the position of OFF-bipolar cell dendrites. alpha3-IR and rho1-IR were rarely found in horizontal cell dendrites innervating rods. We suggest that two GABAergic pathways exist in the outer retina- first, a GABAergic positive loop with GABA receptors mainly on the horizontal cell dendrites and spinules and, second, a GABAergic feedback pathway involving GABA receptors on cone pedicles and GABA transporters on horizontal cells and that this pathway presumably modulates feedback strength from horizontal cells to cones.

Menthol Induces Surgical Anesthesia and Rapid Movement in Fishes

“…GABA A receptors are well known as the predominant ionotropic receptors for fast inhibitory neurotransmission in the CNS. Electrophysiological and/or immunohistochemical studies demonstrate that GABA A -receptors are distributed in the CNS and the retina [26][27][28][29], brainstem [30] and Mauthner cells [31] in goldfish, in the cerebellum of zebrafish [32], and in the optic tectum and the vagal, facial, and glossopharyngeal lobes of the carp [33]. Activation of GABA A receptors induced a decrease in "free-swimming" of the marine teleost that was reflected mostly in explorative type of behaviors during which the animals bumped against objects in the tank or their tank mates, and in an increase of resting states, although GABA A -receptors agonist muscimol induced an increase in the feeding behavior.…”

GABA Transporters Regulate a Standing GABACReceptor-Mediated Current at a Retinal Presynaptic Terminal

“…The GAT-1 subtype of the GABA transporter has previously been localized to the IPL in goldfish (Klooster et al, 2004), salamander , and rat (Johnson et al, 1996) retina. In addition, it has been shown that GAT-1 can limit conventional synaptic activation of bipolar cell GABA C receptors in the salamander retina and influence postsynaptic ganglion cell excitation (Ichinose and Lukasiewicz, 2002).…”

“…Therefore, GABA A receptor-containing synapses may not experience the same elevations in extracellular GABA as the GABA C receptor-containing synapses at the bipolar cell terminal. Importantly, it is known that both GAT-2 and GAT-3 GABA transporters are present along with GAT-1 in the IPL of goldfish retina (Klooster et al, 2004). Thus, these transporters may be colocalized with GABA A receptors and could serve to protect them from elevated extracellular GABA spillover during NO-711 application.…”

Cation Cl− cotransporters in the dendrites of goldfish bipolar cells

“…GABA should have an opposite effect to the glutamate response in Onbipolar and Off-bipolar dendrites. It is known that ionotropic GABA receptors are expressed in both On-bipolar and Off-bipolar dendrites [1,2]. GABA receptors are Cl À -permeable channels, and the effect of GABA largely depends on the local Cl À electrochemical gradient (E Cl ).…”