Responses of Bergmann glia and granule neurons in situ to N-methyl-D-aspartate, norepinephrine, and high potassium.

To gain insight into neuronal-glial signaling in brain, cerebellar Bergmann glia and granule neurons were studied in acutely isolated slices with the aid of laser scanning confocal microscopy. Both Bergmann glia and granule neurons responded to N-methyl-D-aspartate (NMDA) with a rise in [Ca2+]i. However, the glial NMDA response was frequently inhibited by tetrodotoxin, suggesting that the response depended on neuronal action potentials, rather than on direct activation of NMDA receptors on the Bergmann glia. Further experiments demonstrated that the NMDA response in Bergmann glia was not inhibited by a combination of non-NMDA glutamate receptor blockers 6-cyano-7-nitroquinoxaline-2,3-dione and alpha-methyl-4-carboxyphenylglycine. Bergmann glia also responded to norepinephrine and high K+, and the responses were not inhibited by tetrodotoxin. The glial norepinephrine response was blocked by phentolamine but not by the removal of external Ca2+, indicating a direct activation of alpha1-adrenergic receptors that mediated release of Ca2+ from intracellular stores. The KCl-induced response in both neurons and glia was dependent on external Ca2+ and was blocked by verapamil or nifedipine. In summary, our data indicate that Bergmann glia in situ recognize a signal(s) released from neurons during neuronal activity.