Chronic ethanol exposure enhances AMPA-elicited Ca 2+ signals in the somatic and dendritic regions of cerebellar Purkinje neurons

Abstract

Intracellular Ca 2+ signals produced by the glutamate receptor agonist α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA; 5 μM) were measured in the somatic and dendritic regions of cerebellar Purkinje neurons in mature cerebellar control cultures (≥20 days in vitro) and cultures chronically treated with 32 mM ethanol (146 mg%; 8–11 days). Recordings were made in physiological saline without ethanol. The mean peak amplitude of the Ca 2+ signal elicited by AMPA (applied by brief 1-s microperfusion) in the somatic region was enhanced 38% in chronic ethanol-treated Purkinje neurons compared with control neurons. In contrast, Ca 2+ signals evoked by AMPA in the dendritic region were similar in magnitude between control and chronic ethanol-treated Purkinje neurons. When tetrodotoxin (TTX; 500 nM) was included in the bath saline to block spike activity and synaptically-generated events, the mean peak amplitude of the Ca 2+ signal elicited by AMPA was enhanced 60% in both the somatic and dendritic regions of chronic ethanol-treated Purkinje neurons compared with control neurons. Thus, TTX-sensitive mechanisms (i.e., spike or synaptic activity) appear to play a role in normalizing neuronal functions involved in Ca 2+ signaling in the chronic ethanol-treated neurons. In parallel current clamp experiments, the resting membrane potential of chronic ethanol-treated neurons was slightly depolarized compared with control neurons. However, no differences were found between control and chronic ethanol-treated Purkinje neurons in input resistance or the peak amplitude or duration of the depolarizations or hyperpolarizations elicited by AMPA. AMPA receptors mediate fast excitatory neurotransmission in the majority of neurons in the central nervous system (CNS) and Ca 2+ signals in response to AMPA receptor activation contribute to synaptic function. Thus, our results suggest that modulation of Ca 2+ signals to AMPA receptor activation (or other cellular inputs) may provide an important mechanism contributing to the actions of prolonged ethanol exposure in the CNS.