The actions of anandamide on rat superficial medullary dorsal horn neurons in vitro

• Published in: The Journal of physiology 2003-04, Vol.548 (1), p.121-129
• Main Authors: Jennings, E A, Vaughan, C W, Roberts, L A, Christie, M J
• Format: Article
• Language: English
• Subjects: Amidohydrolases - antagonists & inhibitors; Animals; Arachidonic Acids - pharmacology; Capsaicin - analogs & derivatives; Capsaicin - pharmacology; Electric Stimulation; Electrophysiology; Endocannabinoids; Enzyme Inhibitors - pharmacology; Excitatory Postsynaptic Potentials - drug effects; In Vitro Techniques; Medulla Oblongata - cytology; Medulla Oblongata - drug effects; Membrane Potentials - physiology; Nerve Endings - drug effects; Original; Patch-Clamp Techniques; Polyunsaturated Alkamides; Posterior Horn Cells - drug effects; Rats; Rats, Sprague-Dawley; Trigeminal Ganglion - cytology; Trigeminal Ganglion - drug effects
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2002.035063

Whole-cell patch-clamp recordings were made from neurons in the trigeminal nucleus caudalis and trigeminal ganglion, in vitro , to investigate the cellular actions of the endogenous cannabinoid, anandamide. Anandamide has been shown to act through both the cannabinoid receptor 1 (CB1) and the vanilloid receptor 1 (VR1). Anandamide (30 μ m ) caused a 54 % increase in the rate of miniature excitatory post-synaptic currents (mEPSCs), without affecting their amplitude. The effect of anandamide was blocked by the VR1 antagonist capsazepine (20 μ m ), but not by the CB1-specific antagonist AM251 (3 μ m ). Application of the VR1 receptor agonist capsaicin (300 n m ) caused a 4200 % increase in the mEPSC rate. In dissociated trigeminal ganglion neurons, both anandamide and capsaicin caused an outward current in neurons that were voltage clamped at +40 mV. The maximal outward current produced by anandamide (EC 50 , 10 μ m ) was 45 % of that produced by capsaicin (10 μ m ). Co-application of the VR1 antagonist capsazepine (30 μ m ) completely reversed the effects of both capsaicin and anandamide. The anandamide transport inhibitor, AM404 (30 μ m ) caused a 40 % increase in mEPSC rate in the slice preparation and an outward current in dissociated neurons. The latter current was reversed by the VR1 antagonist iodoresiniferatoxin (1 μ m ). The fatty acid amide hydrolase (FAAH) inhibitors phenylmethylsulfonyl fluoride (PMSF) (20 μ m ) and OL53 (1 μ m ) did not enhance the effect of anandamide in either the slice or dissociated neuron preparations. These results suggest that within the superficial medullary dorsal horn, anandamide (30 μ m ) acts presynaptically to enhance the release of glutamate via activation of the VR1 receptor.