Firing properties of respiratory rhythm generating neurons in the absence of synaptic transmission in rat medulla in vitro.
It has previously been demonstrated that Pre-I neurons, localized in the rostral ventrolateral medulla, are important in the generation of the primary respiratory rhythm in brainstem-spinal cord preparations from newborn rats. To investigate whether or not Pre-I neurons have endogenous pacemaker properties, we examined Pre-I neuron activity before and after chemical synaptic transmission was blocked by incubation in a low Ca2+ (0.2 mM), high Mg2+ (5 mM) solution (referred to here as low Ca). After incubation for about 30 min in low Ca, 28 (52%, type-1) out of 54 neurons tested in 27 preparations retained apparent rhythmic (phasic) activity after complete disappearance of C4 inspiratory activity. Sixteen neurons (30%, type-2) fired tonically and 10 (18%, type-3) were silent. We examined the effects of synaptic blockade on 14 inspiratory neurons in the RVL. The firing of all 14 neurons in 9 preparations disappeared concomitantly with the disappearance of C4 activity in low Ca. When the pH of the low Ca solution was lowered with a decrease in NaHCO3 concentration from 7.4 to 7.1, the firing rate of the Pre-I neurons (type-1) increased from 12 to 18/min. In conclusion, the generator of respiratory rhythm in the newborn rat is probably a neuronal network with chemical synapses that functions mainly through the endogenous Pre-I pacemaker cells. Intrinsic chemoreception in the rhythm generator is probably important in frequency control of respiratory rhythm.
Onimaru
H
H
Department of Physiology, Showa University School of Medicine, Tokyo, Japan.
Arata
A
A
Homma
I
I
D000200:Action Potentials; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D002118:Calcium / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000502:physiology; D008526:Medulla Oblongata / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012119:Respiration / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission
D008274:Magnesium; D002118:Calcium