The electrophysiological study of changes in the activities of locus coeruleus neurons under conditions of parathyroidectomy and parathyroid hormone administration

The evoked activity of single neurons in the locus coeruleus (LC) in rats was studied in the norm, after parathyroidectomy (PTX), and after the administration of parathyroid hormone (PTH) during high frequency-stimulation of the supraoptic nucleus of the hypothalamus (SON). Spike activity was analyzed using mathematical software. The excitatory poststimulus neuronal activity in the LC with PTH decreases the average frequency of activity compared to the norm, but it approaches the norm after the introduction of PTH. The poststimulus inhibitory responses of neurons in the LC with PTH were lowered, as compared to the norm; they recovered to the normal level after the introduction of PTH. Calculation of the ratio between the sum of spikes in excitatory poststimulus responses with PTX and the sum in the norm showed a twofold decrease in the responses; after administration of PTH, this sum returned back to normal. However, after PTX we observed an extreme reduction of neurons that responded by excitation as compared to the norm; after PTH administration we found a twofold increase in the number of these neurons as compared to the norm. For the sum of spikes in depression tetanic responses, the introduction of PTH was accompanied by their identical decrease compared to the norm and by an increase in the number of responding neurons after treatment with PTH as compared to both the norm and PTX. Our results led us to conclude that the greater intensity of tetanic responses of poststimulus inhibitory activity apparently results from an activation of the protective inhibitory GABAergic mechanism in intact animals, a sharp deficit of tetanic excitatory effects under conditions of PTX, and the return of these effects to the norm in the presence of PTH.