Changes in glucose do not alter baseline firing rate or chemosensitivity of serotonin neurons cultured from the medullary raphé

A subset of serotonin neurons are putative central respiratory chemoreceptors. To test the hypothesis that serotonin neurons also have intrinsic glucose sensitivity, perforated patch recordings were made from cultured rat medullary raphé neurons after pharmacological blockade of fast glutamatergic and GABAergic synaptic transmission. It has previously been shown that all neurons stimulated by acidosis under these conditions are tryptophan hydroxylase (TPH) immunoreactive. Changes in glucose concentration from 0.1 to 20 mM had no effect on baseline firing rate of 31 neurons that were stimulated by hypercapnic acidosis. The response to hypercapnic acidosis of 25 of these neurons was the same in 0.1, 1, 2, 5 and/or 20 mM glucose as it was in 10 mM glucose. Changes in glucose also did not alter the baseline firing rate of 13 neurons that did not respond to acidosis. Although it is possible that these results were influenced by the use of tissue culture, they do not provide support for intrinsic glucose sensitivity of pH-sensitive serotonin neurons of the medullary raphé.