Electrical synapses between Bergmann glial cells and Purkinje neurones in rat cerebellar slices

In the present study, we directly demonstrated electrical coupling between Bergmann glial cells (BG) and Purkinje neurones (PN) in acutely isolated cerebellar slices, prepared from 15 to 30 days old Sprague-Dawley rats. Electrical coupling between these two cells was identified by dual whole-cell voltage clamp, which allowed direct recording of junctional current. Whole-cell recordings from PN-PN, PN-BG and BG-BG pairs were made using Nomarski optics and infrared visualisation, which allowed precise morphological identification of cells. Junctional currents were recorded by applying hyper/and depolarising voltage sequences ranging from -120 to +40 mV (voltage step 10 mV) to one of the cells in the pair, while ion currents were measured from both cells. As has been shown before, junctional currents were frequently observed in BG-BG pairs: we found electrical coupling in 27 out of 34 pairs analysed. When the similar protocol was applied to the PN-BG pairs, junctional currents were found in 61 out of 87 pairs analysed. The electrical coupling was bi-directional as similar junctional currents were observed in PN when voltage step protocol was applied to BG. No electrical coupling was observed in PN-PN pairs (n = 21). To correlate the appearance of these currents with gap junctions we treated slices with octanol (200 microM) or halothane (500 microM)-known inhibitors of gap junction conductance. Both agents applied for 5 min resulted in a complete inhibition of junctional currents in PN-BG pair. The washout (15 min) led to a complete recovery of junctional currents after treatment with octanol; the action of halothane was irreversible. Finally, we found that filling the BG by Alexa Fluor 488 results in staining of adjacent PN (in 11 out of 23 pairs tested). We conclude therefore that cerebellar neurones and glial cells are directly connected via gap junctions.