Submitted on February 8, 2007
Accepted on June 8, 2007
Cholecystokinin B type receptors mediate a G protein-dependent depolarizing action of cholecystokinin (CCK-8s) on rodent neonatal spinal ventral horn neurons
Murat Oz1*, Keun-Hang Yang2, Toni S Shippenberg1, Leo P. Renaud3, and Michael J O'Donovan2
1 Integrative Neuroscience Section, NIDA, NIH/DHHS, Baltimore, Maryland, United States
2 Laboratory of Neural Control, Section on Developmental Neurobiology, NINDS/NIH, Bethesda, Maryland, United States
3 Division of Neurology/Neurosciences, Ottawa Health Research Institute, Ottawa, Canada
* To whom correspondence should be addressed. E-mail: moz{at}intra.nida.nih.gov.
Reports of cholecystokinin (CCK) binding and expression of CCK receptors in neonatal rodent spinal cord suggest that CCK may influence neuronal excitability. In patch-clamp recordings from 19/21 ventral horn motoneurons in neonatal (PN 5-12 days) rat spinal cord slices, we noted a slowly rising and prolonged membrane depolarization induced by bath applied sulfated CCK octapeptide (CCK-8s; 1 µM), blockable by the CCKB receptor antagonist L-365,260 (1 µM). Responses to non-sulfated CCK-8 or CCK-4 were significantly weaker. Under voltage clamp (VH-65mV), 22 / 24 motoneurons displayed a CCK-8s-induced tetrodotoxin-resistant inward current (peak -136 ± 28 pA) with a similar time course, mediated via reduction in a potassium conductance. In 29/31 unidentified neurons, CCK-8s induced a significantly smaller inward current (peak -42.8± 5.6 pA) and I-V plots revealed either membrane conductance decrease with net inward current reversal at -103.8 ± 4.7 mV (n=16), membrane conductance increase with net current reversing at -37.9 ± 3.6 mV (n=4), or parallel shift (n=9). Intracellular GTP-
-S significantly prolonged the effect of CCK-8s (n=6), whereas GDP-
-S significantly reduced the CCK-8s response (n=6). Peak inward currents were significantly reduced after 5 min perfusion with N-ethylmaleimide. In isolated neonatal mouse spinal cord preparations, CCK-8s (30 nM-300 nM) increased the amplitude and discharge of spontaneous depolarizations recorded from lumbosacral ventral roots. These observations imply functional postsynaptic G-protein coupled CCKB receptors are prevalent in neonatal rodent spinal cord.
