PURPOSE: The purpose of this study was to investigate the activation of the respiratory centers during insufflation of the larynx with CO2 at different flow rates and concentrations. MATERIALS AND METHODS: The experiments were carried out in spontaneous air breathing rabbits, anesthetized with thiopental sodium (25mg kg(-1) i.v.). The larynx was separated from the oropharyngeal cavity and the trachea. The tidal volume (VT) and respiratory frequency (f min(-1)) were recorded from the lower tracheal cannula. The respiratory minute volume (VE) was calculated, the action potentials from the right phrenic nerve were recorded and the inspiratory (TI) and expiratory (TE) periods and the mean inspiratory flow rate (VT/TI) were calculated. The larynx was insufflated at flow rates of 500mL min(-1) and 750mL min(-1), with 7 and 12% CO2-Air by means of a respiratory pump. RESULTS: Insufflation of the larynx, with both gas mixtures, decreased the f and VT significantly. The TI and TE were found to increase significantly due to the decreasing in f. There was a significant decrease in VT/TI ratio. Following bilateral midcervical vagotomy, on the passing of both gas mixtures, significant decreases were observed in the VT, and the responses of f, TI and TE were abolished. After cutting the superior laryngeal nerve, the responses of the VT to both gas mixtures were abolished. CONCLUSION: In conclusion, the results of this study purpose that the stimulation of the laryngeal mechanoreceptors by the effect of hyper- capnia decreases the activation of the respiratory center
Air ; Animals ; Carbon Dioxide/chemistry/*pharmacology ; Female ; Laryngeal Nerves/drug effects/physiology ; Male ; Mechanoreceptors/drug effects/physiology ; Rabbits ; Reflex/*drug effects/physiology ; *Respiratory Mechanics/drug effects ; Tidal Volume

OBJECTIVETo investigate the role of 5-HT1A receptors in the generation and modulation of basic respiration rhythm.

METHODSBrainstem slices of 20 newborn SD rats (0-3 days) were prepared and respiratory rhythmical discharge activity (RRDA) of the hypoglossal nerve was recorded by suction electrode on these preparations including the medial region of the nucleus retrofacialis (mNRF) with the hypoglossal nerve rootlets retained, and the effects of 5-HT1A receptors on RRDA were investigated by application of specific agonist of 5-HT1A receptors 8-OH-DPAT in the perfusion solution. The 20 neonatal rats were divided into 4 groups and the brainstem slices were perfused continuously for 10 min with different concentrations of 8-OH-DPAT (1, 5, 10, 20 micromol/L, respectively). RRDA was recorded before and 1, 3, 5 min after 8-OH-DPAT perfusion.

RESULTSThe respiratory cycles (RC) varied significantly between the different time points of 8-OH-DPAT administration (F=181.219, P<0.001), which was the shortest before 8-OH-DPAT administration and increased progressively after administration till reaching the maximum 5 min after the administration. The RC also varied significantly between different 8-OH-DPAT concentrations (F=61.675, P<0.001). At each time point after 8-OH-DPAT administration, RC was the shortest with 1 micromol/L and maximum with 20 micromol/L 8-OH-DPAT. A crossover effect was observed between the time and administered 8-OH-DPAT concentration (F=22.940, P<0.001). The integrated amplitude (IA) was significantly different between different time points of 8-OH-DPAT administration (F=20.949, P<0.001), and the application of 10 and 20 micromol/L 8-OH-DPAT resulted in significant IA decrement (F=5.050, P=0.017; F=51.389, P=0.001, respectively). Different concentrations of 8-OH-DPAT also significantly affected IA (F=41.027, P<0.001), and at each time point after administration, IA was the maximum with 1 micromol/L and minimum with 20 micromol/L 8-OH-DPAT, also showing a crossover effect between time and 8-OH-DPAT concentration (F=3.483, P=0.002).

CONCLUSIONS8-OH-DPAT induces a dose-dependent increase in RC and a dose-dependent inhibition of the IA and burst frequency, with long-lasting inhibitory effect on the inspiration. 5-HT1A receptors play an important role in the modulation of the RRDA in isolated neonatal rat brainstem slice.

8-Hydroxy-2-(di-n-propylamino)tetralin ; pharmacology ; Animals ; Animals, Newborn ; Brain Stem ; drug effects ; physiology ; Dose-Response Relationship, Drug ; Electric Conductivity ; Electrophysiological Phenomena ; drug effects ; In Vitro Techniques ; Periodicity ; Rats ; Respiratory Mechanics ; drug effects ; physiology ; Time Factors

To compare the effects of ketamine and tiletaminezolazepam (TZ) drugs widely used for the chemical restraint and immobilization of primates, on various physiological parameters and blood gas values in cynomolgus monkeys (Macaca facicularis). Rectal temperature, heart rate, respiration rate and blood gas analysis were measured before treatment and at 1, 10, 20, 30, 40, 50 and 60 min after administration. Additionally, in both groups, induction and maintenance times were compared. Heart rate, respiration rate, rectal temperature, pH and pCO2 were not significant different in the two groups. However, pO2 in the ketamine-treated group was significantly lower at 30 and 40 min than in the TZ-treated group. The induction time was short in both groups, and the maintenance time was longer in the TZ-treated group (67.8+/-6.5 min) than in the ketamine-treated group (42.3+/-6.7 min). However, decreased rectal temperatures must be watched and prevented following TZ administration to cynomolgus monkeys. It was considered that ketamine may be useful for short duration anesthesia including handling, physical examination, blood sampling and TZ may be useful for prolonged anesthesia including minor surgery and other surgical procedure.
Animals ; Body Temperature/drug effects ; Carbon Dioxide/blood ; Excitatory Amino Acid Antagonists/*pharmacology ; Female ; Heart Rate/drug effects ; Hydrogen-Ion Concentration ; Immobilization/*physiology ; Ketamine/*pharmacology ; Macaca fascicularis ; Male ; Partial Pressure ; Respiratory Mechanics ; Restraint, Physical/*methods ; Tiletamine/*pharmacology ; Time Factors