GABA Enhances Transmission at an Excitatory Glutamatergic Synapse

Abstract

GABA mediates both presynaptic and postsynaptic inhibition at many synapses. In contrast, we show that GABA enhances transmission at excitatory synapses between the lateral gastric and medial gastric motor neurons and the gastric mill 6a and 9 (gm6a, gm9) muscles and between the lateral pyloric motor neuron and pyloric 1 (p1) muscles in the stomach of the lobster Homarus americanus. Two-electrode current-clamp or voltage-clamp techniques were used to record from muscle fibers. The innervating nerves were stimulated to evoke excitatory junctional potentials (EJPs) or excitatory junctional currents. Bath application of GABA first decreased the amplitude of evoked EJPs in gm6a and gm9 muscles, but not the p1 muscle, by activating a postjunctional conductance increase that was blocked by picrotoxin. After longer GABA applications (5-15 min), the amplitudes of evoked EJPs increased in all three muscles. This increase persisted in the presence of picrotoxin. beta-(Aminomethyl)-4-chlorobenzenepropanoic acid (baclofen) was an effective agonist for the GABA-evoked enhancement but did not increase the postjunctional conductance. Muscimol activated a rapid postsynaptic conductance but did not enhance the amplitude of the nerve-evoked EJPs. GABA had no effect on iontophoretic responses to glutamate and decreased the coefficient of variation of nerve-evoked EJPs. In the presence or absence of tetrodotoxin, GABA increased the frequency but not the amplitude of miniature endplate potentials. These data suggest that GABA acts presynaptically via a GABA(B)-like receptor to increase the release of neurotransmitter.

PKC-mediated GABAergic enhancement of dopaminergic responses: implication for short-term potentiation at a dual-transmitter synapse

“…Our studies with GABA B agonists and antagonists indicate that GABA-mediated potentiation of dopaminergic currents in B8 is mediated by GABA Blike receptors. GABA, acting at presynaptic sites through GABA B receptors, can enhance or reduce synaptic transmission in both vertebrates (Brenowitz et al 1998) and invertebrates (Gutovitz et al 2001). In our experiments, postsynaptic potentiating actions of GABA were effectively antagonized by the PKC antagonist chelerythrine and mimicked by the PKC agonist PDBu.…”

Incorporating spike-rate adaptation into a rate code in mathematical and biological neurons

“…The actions of neurotransmitters and neuromodulators in the crustacean STNS can be very different from what is commonly observed in vertebrate systems. For instance, acetylcholine has two inhibitory and one depolarizing type of response in STG neurons (Marder and Paupardin-Tritsch 1978), GABA can act presynaptically via a GABA B -like receptor to increase the release of neurotransmitter at neuromuscular junctions (Gutovitz et al 2001), and three classes of serotonin responses in the STG are mediated by distinct serotonin receptor subtypes that show little or no response to vertebrate serotonin antagonists (Zhang and Harris-Warrick 1994). There have been studies of the mechanisms affected by AST and FLRFamides in the C. borealis STNS but not on GPR2 specifically.…”

Structure of the olfactory receptor organs, their GABAergic neural pathways, and modulation of mating behavior, in the giant freshwater prawn,Macrobrachium rosenbergii

“…GABA plays an inhibitory role on the presynaptic signal to the ORNs in the cockroach, Periplaneta americana, and the fruit fly, Drosophila melanogaster (Malun, 1991;Ignell et al, 2009;Wang, 2012), by causing hyperpolarization in the projection neurons (PN) of the ON, resulting in the discrimination of the odors (Wilson and Laurent, 2005). Conversely, the GABA plays excitatory roles in rats and H. americanus (Plotkin et al, 1997;Gutovitz et al, 2001). In H. americanus, GABA is present in the peripheral neuromuscular junction, where it can stimulate the release of glutamate, an excitatory neurotransmitter (Gutovitz et al, 2001).…”

“…Conversely, the GABA plays excitatory roles in rats and H. americanus (Plotkin et al, 1997;Gutovitz et al, 2001). In H. americanus, GABA is present in the peripheral neuromuscular junction, where it can stimulate the release of glutamate, an excitatory neurotransmitter (Gutovitz et al, 2001). Moreover, GABA has been shown to act as the excitatory neurotransmitter on neurosecretory cells in the crayfish, Procambarus clarkii (Garc ıa et al, 1994).…”