Carbenoxolone induced depression of rhythmogenesis in the pre-Bötzinger Complex.
BACKGROUND
Carbenoxolone (CBX), a gap junction uncoupler, alters the functioning of the pre-Bötzinger Complex (preBötC), a central pattern generating neuronal network important for the production of respiratory rhythm in mammals. Even when isolated in a 1/2 mm-thick slice of medulla oblongata from neonatal mouse the preBötC continues producing periodic bursts of action potentials, termed population bursts that are thought to be important in generating various patterns of inspiration, in vivo. Whether gap junction communication contributes to preBötC rhythmogenesis remains unresolved, largely because existing gap junction uncouplers exert numerous non-specific effects (e.g., inhibition of active transport, alteration of membrane conductances). Here, we determined whether CBX alters preBötC rhythmogenesis by altering membrane properties including input resistance (Rin), voltage-gated Na+ current (INa), and/or voltage-gated K+ current (IK), rather than by blocking gap junction communication. To do so we used a medullary slice preparation, network-level recordings, whole-cell voltage clamp, and glycyrrhizic acid (GZA; a substance used as a control for CBX, since it is similar in structure and does not block gap junctions).


RESULTS
Whereas neither of the control treatments [artificial cerebrospinal fluid (aCSF) or GZA (50 muM)] noticeably affected preBötC rhythmogenesis, CBX (50 muM) decreased the frequency, area and amplitude of population bursts, eventually terminating population burst production after 45-60 min. Both CBX and GZA decreased neuronal Rin and induced an outward holding current. Although neither agent altered the steady state component of IK evoked by depolarizing voltage steps, CBX, but not GZA, increased peak INa.


CONCLUSIONS
The data presented herein are consistent with the notion that gap junction communication is important for preBötC rhythmogenesis. By comparing the effects of CBX and GZA on membrane properties our data a) demonstrate that depression of preBötC rhythmogenesis by CBX results from actions on another variable or other variables; and b) show that this comparative approach can be used to evaluate the potential contribution of other non-specific actions (e.g., Ca++ conductances or active transport) of CBX, or other uncouplers, in their alteration of preBötC rhythmogenesis, or the functioning of other networks.
Elsen
Frank P
FP
Department of Neurology, Medical College of Wisconsin, Milwaukee, WI 53226, USA. felsen@mcw.edu
Shields
Edward J
EJ
Roe
Matthew T
MT
Vandam
Richard J
RJ
Kelty
Jonathan D
JD
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D000897:Anti-Ulcer Agents / Q000494:pharmacology; D017776:Autonomic Pathways / Q000187:drug effects / Q000502:physiology; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology; D002229:Carbenoxolone / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D005260:Female; D019695:Glycyrrhizic Acid / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D010507:Periodicity; D012119:Respiration / Q000187:drug effects*; D012125:Respiratory Center / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D000893:Anti-Inflammatory Agents; D000897:Anti-Ulcer Agents; D019695:Glycyrrhizic Acid; D002229:Carbenoxolone