The respiratory role of the ventral surface of the medulla studied in the anaesthetized rat.

Abstract

SUMMARY1. The respiratory role of the ventral surface of the medulla was studied in rats anaesthetized with a urethane-chloralose mixture.2. In fifty-eight studies on twelve animals, direct superfusion of the medullary surface with artificial c.s.f. made acid by the reduction of bicarbonate content or by the increase of P003 produced no significant stimulation of respiration provided that the temperature of the brain surface was unaltered.3. Superperfusion of the medullary surface with c.s.f. of low bicarbonate content produced an inhibition of respiration in fourteen of thirty-eight experiments.4. Electrical stimulation on the surface revealed a localized area lateral to the pyramids and rostral to the XIIth nerve where stimulation at low intensity produced an increase in the frequency and depth of respiration.5. The application of carbachol to a similar region increased both the frequency and amplitude of ventilation at lower concentrations than were required to obtain effects from surrounding areas.6. Sudden switching between perfusates at different temperatures produced changes of ventilation within 1-2 see of a change of surface temperature. The Q10 for the ventilation/temperature relationship was approximately 6. 7. The experiments confirm that the ventral surface of the medulla contains neural elements which, at least during urethane-chloralose anaesthesia, have a significant effect on respiration. The stimulus for these effects in the rat does not appear to be a change in H+ concentration. It appears more probable that the primary role of the area lies in the link between thermal and respiratory regulation.

Effects of Urethane-Chloralose Anaesthesia on Respiration in the Rat

“…The anaesthetized rat is being used increasingly for studies of respiratory control (Hanna, Drysdale & Cragg, 1979;Hori, Roth & Yamamoto, 1970;Laha, Nayar, Chhina & Singh, 1977;Lai, Tsuya & Hildebrandt, 1978;Malcolm, Sarelius & Sinclair, 1980). The effect of pentobarbitone on alveolar and arterial gas levels has been demonstrated (Cragg & Drysdale, 1979) but generally the effects of anaesthetic regimes in the rat have not been assessed to the same extent as in the rabbit (Korner, Uther & White, 1968; Blake & Korner, 1980), cat (Wang & Nims, 1948; F16rtz & Borison, 1%9) and dog (Ledsome, Linden & Norman, 1971).…”

Cooling of ventral medullary intermediate areas and respiration in the cat.

“…I areas are shut down. A few reports failed, however, to substantiate the crucial role of the VMS in the chemoceptive function (COzINE and NGAI, 1967;LIPSCOMB and BOYARSKY, 1972;CRAGG et al, 1977;MALCOLM et al, 1980). We hypothesized that the inhibitory effects ascribed specifically to blockade of the I areas may rather depend on the decline in the combined power of reflux inputs reaching and influencing the CRC.…”

5-HT Neurons and CO₂ chemoreception

“…However, some argue that these superficial regions are not the only site of central chemosensitivity, and that deeper areas are CO2-sensitive (Cozine and Ngai, 1967;Cragg et al, 1977;Kiley et al, 1985;Lipscomb and Boyarsky, 1972;Malcolm et al, 1980;Pappenheimer et al, 1965).…”