Modulation of hippocampal GABAergic currents by anti-gephyrin intrabodies (delta2-188)

The efficiency of synaptic transmission relies on the temporally and spatially regulated expression of postsynaptic receptors localized in precise apposition to presynaptic release sites. At synapses, receptors are organized in clusters which are formed by highly regulated events, dynamically controlled by a number of proteins including scaffolds, adhesion molecules and active transport processes along the cytoskeleton (Kneussel and Loebrich, 2007). At inhibitory synapses, GABAergic signaling controls dendritic integration, neural excitability, circuit reorganization and fine tuning of network activity. Among different players, the tubulin-binding protein gephyrin, plays a key role in anchoring GABAA receptors to synaptic membranes, (Tyagarajan and Fritschy, 2014). Moreover, gephyrin is instrumental in establishing and maintaining a proper excitatory (E)/inhibitory (I) balance necessary for the correct functioning of neuronal networks (Pizzarelli and Cherubini, 2011). A disruption of the E/I balance is thought to be at the origin of several neuropsychiatric disorders including epilepsy, schizophrenia and autism (Penzes et al. 2013; Cellot and Cherubini, 2014; Nelson and Valakh, 2015). We tested the effects of truncated form of gephyrin (delta 2-188), acting as a dominant negative protein, on spontaneous inhibitory postsynaptic currents, sIPSCs, from hippocampal neurons in culture. In cells transfected with delta 2-188 fused to EGFP or with EGFP alone, the mean sIPSCs frequency was 0.91 ± 0.18 Hz in control (n=10) and 0.42 ± 0.09 Hz in the presence of delta 2-188 (n=9). The mean sIPSCs amplitude was 129.4 ± 18.8 pA in controls and 81.9 ±m13.2 pA in the presence of delta 2-188. Significant differences were found between controls and delta 2-188 regarding the frequency and amplitude of sIPSCs (p=0.03 and p=0.05, respectively). These data further support the hypothesis that gephyrin regulates the postsynaptic organization of synaptic GABAA receptors. Andjus, P R, Stevic‐Marinkovic, Z and Cherubini E (1997) Immunoglobulins from motoneurone disease patients enhance glutamate release from rat hippocampal neurones in culture. The Journal of Physiology, 504: 103-112 Cellot G, Cherubini E (2014) GABAergic signaling as therapeutic target for autism spectrum disorders. Front Pediatr 2:70. doi: 10.3389/fped.2014.00070 Kneussel M, Loebrich S (2007) Trafficking and synaptic anchoring of ionotropic inhibitory neurotransmitter receptors. Biol Cell 99: 297-309 Nelson SB, Valakh V (2015) Excitatory/Inhibitory Balance and Circuit Homeostasis in Autism Spectrum Disorders. Neuron 87: 684-698 Penzes P, Buonanno A, Passafaro M, Sala C, Sweet RA (2013) Developmental vulnerability of synapses and circuits associated with neuropsychiatric disorders. J Neurochem 126:165-82 Pizzarelli R, Cherubini E (2011) Alterations of GABAergic signaling in autism spectrum disorders. Neural Plast 297153. doi: 10.1155/2011/297153 Tyagarajan SK, Fritschy JM (2014) Gephyrin: a master regulator of neuronal function? Nat Rev Neurosci 15: 141-156