An Interesting Molecule: γ-Aminobutyric Acid. What Can We Learn from Hydra Polyps?

Abstract

Neuronal excitability is controlled primarily by γ-aminobutyric acid (GABA) in the central and peripheral nervous systems of vertebrate as well as invertebrate organisms. Besides its recognized neurotransmitter functions, GABA also plays a fundamental role in neurogenesis and synaptogenesis during embryonic development. In addition, GABAergic mechanisms are also involved in disorders of various peripheral tissues, ranging from diabetes to hypothyroidism to inflammatory responses. The discovery of the molecule and the history of its biosynthetic pathways in vertebrate and invertebrate phyla are summarized here. The occurrence and distribution of GABA, GABA-synthesizing enzymes, and receptors to GABA in the freshwater polyp Hydra vulgaris (Cnidaria: Hydrozoa), endowed with an early evolved nervous system, are discussed in relation to possible interactions with the microbiota, a stable component of Hydra polyps; their contribution to the evolution of nervous systems through microbe–neuronal interactions is proposed.

Stimulation of GABA Receptors in the Lateral Septum Rapidly Elicits Food Intake and Mediates Natural Feeding

“…Given that GABA A receptor activation is, with rare exceptions, inhibitory in mature mammals [ 20 ], the predicted impact of GABA on the LS neurons expressing GABA A receptors is to inhibit their neural activity. Consequently, it would seem that GABA A receptor activation in the LS elicits eating by inhibiting neurons that inhibit eating.…”

“…Gamma-aminobutyric acid (GABA) is the dominant inhibitory neurotransmitter in the central nervous system [ 20 ] via its actions on GABA A and GABA B receptors. Since the predominant type of neuron in the LS is the medium-sized GABAergic spiny projection neuron [ 21 ], it is unsurprising that LS GABA receptors are involved in inhibitory feeding mechanisms.…”

GABAergic signaling shapes multiple aspects ofDrosophilacourtship motor behavior

“…Neuronal inhibition is a universal feature of nervous systems. Fast neuronal inhibition is accomplished by GABA, a neurotransmitter conserved across vertebrates and invertebrates that is already present in the simple nerve nets of cnidaria (Rentzsch et al 2019, Arendt 2020, Pierobon 2021. GABAergic inhibition in the nervous system is important for stabilizing and shaping network activity and counterbalancing excitation, allowing for efficient coding and preventing runaway excitation and epileptic seizure (Cossart et al 2005, Hennequin et al 2017, Yu and Yu 2017, Smart and Stephenson 2019.…”

GABAergic signaling shapes multiple aspects of Drosophila courtship motor behavior

“…Fast neuronal inhibition is accomplished by GABA, a neurotransmitter conserved across vertebrates and invertebrates that is already present in the simple nerve nets of cnidaria. 1 , 2 , 3 GABAergic inhibition in the nervous system is important for stabilizing and shaping network activity and counterbalancing excitation, allowing for efficient coding and preventing runaway excitation and epileptic seizure. 4 , 5 , 6 , 7 , 8 Additional to this global and general role, inhibitory connections shape circuit motifs that enable computations performed in many different pathways across many different species.…”