The goal of this proposal is to investigate the role and properties of gap junction-mediated electrical synapses in the auditory system. Auditory afferents terminating as large mixed (electrical and chemical) synaptic terminals on the goldfish Mauthner cell are ideally suited for these studies since unlike mammalian electrical synapses, the experimental accessibility makes it possible to quantify in vivo changes in junctional conductance that occur under different physiological conditions and to correlate them with anatomical, ultrastructural and molecular analysis. Strikingly, the conductance of these model electrical synapses is under the fine regulatory control of neuronal activity. Electrical transmission is mediated by connexin 35 (Cx35), the fish ortholog of the mammalian connexin 36 (Cx36) which is present in the auditory system, suggesting that mammalian auditory electrical synapses could be similarly regulated. This proposal deals on understanding the molecular mechanisms underlying the bi-directional control of junctional conductance at these terminals by focusing in the role of regulated trafficking of gap junction channels.
Aim 1 is to investigate the existence of trafficking of gap junction channels at native electrical synapses, in vivo, by combining ultrastructural and pharmacological approaches. Our preliminary results suggest the existence of an active turnover of gap junction channels, which constitute the first evidence of this phenomenon in a native synapse.
Aim 2 is to determine the contribution of regulated trafficking to activity-dependent potentiation of electrical transmission. It will test if mechanisms of exocytosis are required for the expression of the potentiation and if it requires of direct interactions with the regulatory kinase CaM-KII and the scaffold protein ZO-1. Conversely, Aim 3 will investigate the possible contribution of regulated trafficking to activity-dependent depression of electrical transmission. Using similar approaches, we will investigate if mechanisms of endocytosis are required for activity-dependent depression of junctional conductance, as well the potential roles of direct protein-protein interactions. Furthermore, the direct interactions of CaM-KII and ZO-1 through conserved regions of both Cx35 and Cx36 suggests that its function might underlie a fundamental and widespread property of electrical transmission, also relevant to mammalian electrical synapses. Thus, the proposed research addresses the novel concept that the strength of electrical synapses is achieved by dynamically regulating the trafficking of gap junction channels. Because electrical synapses have been shown to promote coordinated neuronal activity, dysfunction of this regulation could have profound pathological implications, contributing to auditory impairment, epilepsy and cognitive (psychiatric) and developmental disorders

Public Health Relevance

The proposal explores the molecular mechanisms involved in the regulation of gap junction-mediated electrical synapses. Further, the proposal explores the role of regulated trafficking of gap junction channels as their underlying mechanism. This process has been shown involved in the regulation of chemical synapses, but no evidence suggests its participation in electrical synapses. Thus, the proposal investigates the possibility that both chemical and electrical synapses share common regulatory mechanisms. Because electrical synapses have been shown to promote coordinated neuronal activity, dysfunction of their regulation could have profound pathological implications, contributing to epilepsy and to cognitive (psychiatric) and developmental disorders.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Auditory System Study Section (AUD)
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Cyr, Janet
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Albert Einstein College of Medicine
Schools of Medicine
United States
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Jain, Roshan A; Wolman, Marc A; Marsden, Kurt C et al. (2018) A Forward Genetic Screen in Zebrafish Identifies the G-Protein-Coupled Receptor CaSR as a Modulator of Sensorimotor Decision Making. Curr Biol 28:1357-1369.e5
Nagy, James I; Pereda, Alberto E; Rash, John E (2018) Electrical synapses in mammalian CNS: Past eras, present focus and future directions. Biochim Biophys Acta Biomembr 1860:102-123
Faber, Donald S; Pereda, Alberto E (2018) Two Forms of Electrical Transmission Between Neurons. Front Mol Neurosci 11:427
Miller, Adam C; Pereda, Alberto E (2017) The electrical synapse: Molecular complexities at the gap and beyond. Dev Neurobiol 77:562-574
Pereda, Alberto E; Macagno, Eduardo (2017) Electrical transmission: Two structures, same functions? Dev Neurobiol 77:517-521
Nagy, James I; Pereda, Alberto E; Rash, John E (2017) On the occurrence and enigmatic functions of mixed (chemical plus electrical) synapses in the mammalian CNS. Neurosci Lett :
Haas, Julie S; Greenwald, Corey M; Pereda, Alberto E (2016) Activity-dependent plasticity of electrical synapses: increasing evidence for its presence and functional roles in the mammalian brain. BMC Cell Biol 17 Suppl 1:14
Rash, J E; Kamasawa, N; Vanderpool, K G et al. (2015) Heterotypic gap junctions at glutamatergic mixed synapses are abundant in goldfish brain. Neuroscience 285:166-93
Cachope, Roger; Pereda, Alberto E (2015) Opioids potentiate electrical transmission at mixed synapses on the Mauthner cell. J Neurophysiol 114:689-97
Yao, Cong; Vanderpool, Kimberly G; Delfiner, Matthew et al. (2014) Electrical synaptic transmission in developing zebrafish: properties and molecular composition of gap junctions at a central auditory synapse. J Neurophysiol 112:2102-13

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