Sodium and calcium current-mediated pacemaker neurons and respiratory rhythm generation.
The breathing motor pattern in mammals originates in brainstem networks. Whether pacemaker neurons play an obligatory role remains a key unanswered question. We performed whole-cell recordings in the preBotzinger Complex in slice preparations from neonatal rodents and tested for pacemaker activity. We observed persistent Na+ current (I(NaP))-mediated bursting in approximately 5% of inspiratory neurons in postnatal day 0 (P0)-P5 and in P8-P10 slices. I(NaP)-mediated bursting was voltage dependent and blocked by 20 mum riluzole (RIL). We found Ca2+ current (I(Ca))-dependent bursting in 7.5% of inspiratory neurons in P8-P10 slices, but in P0-P5 slices these cells were exceedingly rare (0.6%). This bursting was voltage independent and blocked by 100 microm Cd2+ or flufenamic acid (FFA) (10-200 microm), which suggests that a Ca2+-activated inward cationic current (I(CAN)) underlies burst generation. These data substantiate our observation that P0-P5 slices exposed to RIL contain few (if any) pacemaker neurons, yet maintain respiratory rhythm. We also show that 20 nm TTX or coapplication of 20 microm RIL + FFA (100-200 microm) stops the respiratory rhythm, but that adding 2 mum substance P restarts it. We conclude that I(NaP) and I(CAN) enhance neuronal excitability and promote rhythmogenesis, even if their magnitude is insufficient to support bursting-pacemaker activity in individual neurons. When I(NaP) and I(CAN) are removed pharmacologically, the rhythm can be maintained by boosting neural excitability, which is inconsistent with a pacemaker-essential mechanism of respiratory rhythmogenesis by the preBotzinger complex.
Del Negro
Christopher A
CA
Systems Neurobiology Laboratory, Department of Neurobiology, David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, California 90095-1763, USA. cadeln@wm.edu
Morgado-Valle
Consuelo
C
Hayes
John A
JA
Mackay
Devin D
DD
Pace
Ryland W
RW
Crowder
Erin A
EA
Feldman
Jack L
JL
D000818:Animals; D000831:Animals, Newborn; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D001933:Brain Stem / Q000166:cytology / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D005439:Flufenamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D008526:Medulla Oblongata / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012125:Respiratory Center / Q000502:physiology; D012137:Respiratory System / Q000294:innervation*; D019782:Riluzole / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D015220:Calcium Channels; D015222:Sodium Channels; D013779:Tetrodotoxin; D005439:Flufenamic Acid; D019782:Riluzole