GABA-mediated Ca2+ signalling in developing rat cerebellar Purkinje neurones

1. Cellular responses to GABA(A) receptor activation were studied in develo ping cerebellar Purkinje neurones (PNs) in brain slices obtained from 2- to 22-day-old rats. Two-photon fluorescence imaging of fura-2-loaded cells an d perforated-patch recordings were used to monitor intracellular Ca2+ trans ients and to estimate the reversal potential of GABA-induced currents, resp ectively. 2. During the 1st postnatal week, focal application of GABA or the GABA(A) receptor agonist muscimol evoked transient increases in [Ca2+](i) in immatu re PNs. These Ca2+ transients were reversibly abolished by the GABAA recept or antagonist bicuculline and by Ni2+, a blocker of voltage-activated Ca2channels. 3. Perforated-patch recordings were used to measure the reversal potential of GABA-evoked currents (E-GABA) at different stages of development. It was found that E-GABA was about -44 mV at postnatal day 3 (P3), it shifted to gradually more negative values during the 1st week and finally equilibrated at -87 mV at around the end of the 2nd postnatal week. This transition was well described by a sigmoidal function. The largest change in EGABA was -7 mV day(-1), which occurred at around P6. 4. The transition in GABA-mediated signalling occurs during a period in whi ch striking changes in PN morphology and synaptic connectivity are known to take place. Since such changes were shown to be Ca2+ dependent, we propose that GABA-evoked Ca2+ signalling is one of the critical determinants for t he normal development of cerebellar PNs.