SHORT COMMUNICATION GABA in developing rat skeletal muscle and motor neurons Gusel V. Sibgatullina 1 & Artem I. Malomouzh 1,2 Received: 26 June 2019 /Accepted: 28 January 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020 Abstract In recent years, considerable evidence is accumulated pointing to participation of gamma-aminobutyric acid (GABA) in inter- cellular signaling in the peripheral nervous system, including, in particular, neuromuscular transmission. However, where in the neuromuscular synapse GABA is synthesized remains not quite clear. We used histochemical methods to detect GABA and L- glutamate decarboxylase (GAD) in developing skeletal muscle fibers and in cultured motor neurons. We found that GABA can be detected already in myocytes, but with further muscle maturation, GABA synthesis gradually attenuates and completely ceases in early postnatal development. We found also that formation of GABA in muscle tissue does not depend on activity of GAD, but presumably proceeds through some other, alternative pathways. In motor neurons, GABA and GAD can be detected at the early stage of development (prior to synapse formation). Our data support the hypothesis that GABA and GAD, which are detectable in adult neuromuscular junctions, have neuronal origin. The mechanism of GABA production and its role in devel- oping muscle tissue need further clarification. Keywords Neuromuscular junction . Myocytes . Skeletal muscle fiber . Motor neuron . GABA . L-Glutamate decarboxylase Introduction Gamma-aminobutyric acid (GABA) is an amino acid recog- nized to be a major inhibitory neurotransmitter in the central nervous system, where it plays a pivotal role in development, maturation, and functioning of the adult brain. However, dur- ing the last few decades, the data were accumulated pointing to potential signaling role of GABA in different branches of the peripheral nervous system (Erdö and Wolff 1990; Elinos et al. 2016; Koussoulas et al. 2018). In particular, GABA is active in synaptic contacts between motor neurons and skele- tal muscle fibers (Borodinsky and Spitzer 2007; Malomouzh et al. 2015; Nurullin et al. 2018). In preliminary studies, we showed that GABA, L-glutamate decarboxylase (GAD)—a major enzyme for GABA synthesis, transmembrane trans- porters for amino acids (Nurullin et al. 2018), and metabotro- pic GABA B receptors are all present in the area of adult mam- malian neuromuscular junction (Malomuzh et al. 2015). Activation of these receptors by an exogenous agonist led to inhibition of acetylcholine release from motor nerve endings (Malomouzh et al. 2015). This suggests that GABA may play a specific signaling role in function of peripheral cholinergic neuromuscular synapse. At the same time, there is no defini- tive answer to the question: in which compartments of the synapse are GABA and GAD present? In addition, there is also no information about whether the expression of GAD and the localization of GABA molecules change during the devel- opment of muscle and nerve tissues. It has been repeatedly shown the GABAergic system undergoes profound functional and structural changes during ontogenesis (Frahm and Draguhn 2001), including expression of certain proteins of this signaling system in immature cells and their complete absence in mature ones (Yan and Ribak 1998). Borodinsky and Spitzer (2007) observed the expression of functional GABA A receptors in cultured Xenopus myocytes which completely ceased after formation of synaptic contacts with neurons that also testifies in favor of putative changes in the peripheral synapses during development. Thus, the aim of the Handling Editor: Pavel Dráber Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00709-020-01485-1) contains supplementary material, which is available to authorized users. * Artem I. Malomouzh artur57@gmail.com 1 Kazan Institute of Biochemistry and Biophysics, FRC Kazan Scientific Center, Russian Academy of Sciences, Kazan 420111, Russia 2 Kazan (Volga Region) Federal University, Kazan 420008, Russia Protoplasma https://doi.org/10.1007/s00709-020-01485-1