1. The effects of nociceptin/orphanin FQ (N/OFQ) and opioid receptor agonists on voltage-activated calcium channel currents (ICa) were examined in acutely isolated mouse trigeminal ganglion neurons using whole-cell patch-clamp recordings. These effects were correlated with responses of the neurons to capsaicin and binding of Bandeiraea simplicifolia isolectin B4 (IB4). 2. Trigeminal neurons were divided into two populations based on the presence (type 2) or absence (type 1) of a prominent T-type ICa. N/OFQ potently (EC50 of 19 nM) inhibited high-voltage-activated (HVA) ICa in most (82%) small (capacitance < 12 pF) type 1 neurons, but few (9%) larger (> 12 pF) type 1 neurons. N/OFQ inhibited ICa in few (23%) type 2 cells, and did not affect the T-type ICa in any cell. 3. The μ-opioid agonists DAMGO and morphine inhibited ICa in most type 1 neurons, more often (95% versus 77%) in the small cells. The inhibition of ICa by DAMGO and morphine was more efficacious in small versus large type 1 neurons. μ-Opioids did not inhibit ICa in type 2 neurons. 4. Most small type 1 neurons were sensitive to capsaicin (93%) and bound IB4 (86%). Fewer larger type 1 neurons responded to capsaicin (30%) or bound IB4 (58%). Type 2 neurons did not respond to capsaicin, although some bound IB4 (35%). 5. Thus, N/OFQ preferentially inhibits HVA ICa in a subpopulation of small nociceptive trigeminal ganglion neurons that is also highly sensitive to μ-opioid agonists.
|Number of pages||13|
|Journal||Journal of Physiology|
|Publication status||Published - 1 Oct 2001|