Lactate dehydrogenase isoenzymes in sympathetic neurons and satellite gliocytes in normal conditions and in blockade of nicotinic cholinoreceptors

Integral cytophotometry was used to measure lactate dehydrogenase (LDH) and its H-and M-isoforms in neurons and satellite gliocytes in tissue sections from the cranial cervical sympathetic ganglion of the rabbit in normal conditions and after experimental partial and complete pharmacological blockade of nicotinic cholinoreceptors (n-CR). In normal conditions, both cell types showed both the H-and M-type isoforms, though the isoenzyme profiles differed — neurons showed a dominance of H-isoform activity while the M-isoform was more active in satellite gliocytes. In partial and complete blockade, the activity of LDH and its H-and M-isoforms decreased significantly in proportion to the number of blocked n-CR. In satellite gliocytes, increases in the extent of blockade were associated with decreases in the activity only of the M-isoform, while the activity of the H-isoform did not change. In partial blockade, the LDH isoenzyme profile of satellite gliocytes shifted towards the neuronal isoform, while in complete blockade there was no difference from the LDH isoenzyme profile of intact neurons. These data led to the suggestion that the formation of lactate in satellite gliocytes is induced by nicotinic cholinergic synapses directly involved in neuron-glial interactions and in controlling the activity of the LDH enzyme system in sympathetic neurons.