Spinal administration of receptor-selective drugs as analgesics: new horizons

The processing at the spinal cord levels of sensory information is subject to modulation by a number of local receptor systems, including opioids: alpha 2 adrenergic; and to a lesser extent serotonin, GABAB, neuropeptide Y, cholinergic, adenosine, and the NMDA-glutamate site. The functional utility of these multiple systems are only partially understood, but it appears that (a) they may act individually to alter different aspects of the nociceptive sensory message (b) they could be used synergistically to reduce the incidence of side effects by reducing the dose of agents required to yield analgesic effects, and (c) they may function variably in animals made tolerant to classes of receptor agonists.