NMDA Receptor Activation and Ca²⁺/PKC Signaling in Nicotine-Induced GABA Transport Shift in Embryonic Chick Retina

Nicotinic receptors are present in the retina of different vertebrates, and in the chick retina, it is present during early development throughout to post-hatching. These receptors are activated by nicotine, an alkaloid with addictive and neurotransmitter release modulation properties, such as GABA signaling. Here we evaluated the mechanisms of nicotine signaling in the avian retina during the development of neuron-glia cells at a stage where synapses are peaking. Nicotine almost halved [³H]-GABA uptake, reducing it by 45% whilst increasing more than two-fold [³H]-GABA release in E12 embryonic chick retinas. Additionally, nicotine mediated a 33% increase in [³H]-D-aspartate release. MK-801 50 μM blocked 66% of nicotine-induced [³H]-GABA release and Gö 6983 100 nM prevented the nicotine-induced reduction in [³H]-GABA uptake by rescuing 40% of this neurotransmitter uptake, implicating NMDAR and PKC (respectively) in the nicotinic responses. In addition, NO-711 prevented [³H]-GABA uptake and release induced by nicotine. Furthermore, the relevance of calcium influx for PKC activation was evidenced through fura-2 imaging. We conclude that the shift of GABA transport mediated by nicotine promotes GABA release by inducing transporter reversal via nicotine-induced EAA release through EAATs, or by a direct effect of nicotine in activating nicotinic receptors permeable to calcium and promoting PKC pathway activation and shifting GAT-1 activity, both prompting calcium influx, and activation of the PKC pathway and shifting GAT-1 activity.