Correlation Of Excitatory And Depressive Synaptic Processes In Spinal Cord Motoneurons In Hypocalcemia Development Dynamics In Parathyroidectomized Rats

Bilateral parathyroidectomy was conducted in experimental animals, and after 3-7 and 21-22 days an isolated spinal cord was obtained by its transection at T2-T3 level under novocaine and immobilization by ditillinum. Registration of activity from motoneurons of the spinal cord L4-L5 segments to 1-second high-frequency stimulation of flexor (n. Gastrocnemius, G) and extensor (n. Peroneus communis, P) hind limb nerves was performed. Tetanic and posttetanic potentiation and depression were recorded. The analysis of post-stimulus activity was produced by on-line selection and program analysis of the spikes. The average peri-event time histogram of the interspike intervals, cumulative histograms of spikes number and average frequency histograms were used. Overall, 295 neurons were recorded. Background activity of the flexor motoneurons decreased by the 3rd day and was growing progressively since days 4-5 (up to 1.5 times), reached 1.1-fold underestimation by day 22, while those of the extensors, growing by the 4th day, reduced to the same value at day 22. At 50 Hz high-frequency stimulation of the nerve G only on day 22 tetanic potentiation of motoneurons approached the norm, while the tetanic potentiation to 100 Hz in all the days of testing was above norm, progressively growing up to 4.7-fold exceeding. In response to 50 Hz the high-frequency stimulation of P nerve, starting from the 7th day tetanic potentiation of motoneurons increased up to 1.6-fold excess of norm, while to 100 Hz already at the 3rd day it was observed to exceed the norm progressively growing by the 22nd day, likewise the case of nerve G. The tetanic depression of motoneurons to 50 Hz high-frequency stimulation of nerve G, increasing from day 4 to 21 reached 2.3-fold excess of norm; then, at 100 Hz already from the 4th to the 7th day twice exceeding the norm, and at the 21st day it dropped up to 1.5 times. The tetanic depression of motoneurons to 50 Hz high-frequency stimulation of P nerve, already at the 4th and until the 21st day reached a 1.5-fold excess, at the 22nd day approached the norm and in response to 100 Hz, being at the 4th day 3 times higher than norm, decreased up to twofold exceeding of norm at the 7th day, reaching the level of norm at the 22nd day. In general, with the pathology development there was an abrupt increase of excitatory and depressor effects, but by the end of tests only depressor effects reached the norm.The posttetanic potentiation and posttetanic depression of motoneurons to high-frequency stimulation of both nerves, likewise the norm, accompanied tetanic potentiation in all the terms. The tetanic depression of motoneurons to high-frequency stimulation of G nerve changed into the posttetanic potentiation in the early days and later on into posttetanic depression; the tetanic depression of nerve P equally turned in both terms, while in norm tetanic depression from both nerves changed into posttetanic potentiation in response to 100 Hz and into the posttetanic depression under 50 Hz.