Non-cholinergic excitation in neurons after a chronic glutamate receptor blockade.

Previous experiments revealed a dramatic increase in excitatory acetylcholine transmission in hypothalamic cultures during a chronic decrease in glutamate activity. Data suggested that in the absence of glutamate excitation, acetylcholine becomes the major excitatory neurotransmitter. However, non-cholinergic excitatory activity was also detected in some neurons. Here, using calcium imaging in hypothalamic cultures chronically subjected to the glutamate receptor blockade, we demonstrate the contribution of metabotropic glutamate receptors, P2-purinoreceptors, histamine receptors, adrenoreceptors, and gap junctions, but not nitric oxide to this non-cholinergic excitation. We also show that the sensitivity of neurons to receptor agonists is increased following the blockade. Data suggest that multiple components contribute to the excitatory activity in hypothalamic neurons during a long-term decrease in glutamate activity.