Abstract
Effects of a non-competetive blocker of glutamate NMDA receptors, ketamine, on respiratory activity recorded from the phrenic nerve were studied in experiments on superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of 3− to 4-day-old rats. The experiments were carried out under conditions where the ventrolateral medullary region (VLM) was left intact, or its rostral portion (projectionally corresponding to the chemosensitiveM zone) was separated by transection. Three-min-long application of 1.0 μM ketamine evoked a slight increase in the duration of inspiratory discharges (ID) and a statistically significant increase in their frequency. After the rostral VLM had been separated, similar ketamine application resulted in significant increases in the duration, amplitude, and integral intensity of ID and some drop in their frequency. An increase to 10 μM ketamine concentration in the superfusing solution determined a significant rise of the ID duration, which indicates the possibility of inhibition of the mechanisms switching inspiration to expiration. Concurrently, the ID frequency significantly dropped, while their amplitude and integral intensity increased. After separation of the rostral VLM, the latter ketamine concentration ceased to increase the ID duration, and their frequency and amplitude significantly dropped. Application of ketamine in the concentration of 100 μM resulted in rather profound decreases of all measured ID parameters, and separation of the rostral VLM exerted no influence on the direction of the above modifications. Thus, we obtained evidence of the involvement of NMDA receptors of the VLM in the control of temporal and frequency-amplitude parameters of respiratory activity of early postnatal rats. Possible localization of NMDA receptors and mechanisms of their involvement in inspiration-expiration switching and tonic inhibitory control of respiratory rhythms are discussed.
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