Low current transcranial electrostimulation (TE) has been shown to induce analgesia, modifying responses to acute noxious stimuli. The analgesic effects of TE may be blocked by Naloxone. Similar forms of electrostimulation have been shown to potentiate morphine analgesia. TE has been used to substantially reduce symptom occurrence in opiate withdrawal syndrome in morphine addicted rats. These effects are enhanced following application of enkephalinase inhibitors or L- tryptophan with TE. Experiments on single neurons have revealed periventricular regions (nuclei) susceptible to TE which participate in the nociceptive neuro-axis. Experiments have shown the amplitude of the thalamic component of sub-cortical evoked potentials is suppressed with morphine induction where the components radiating from the spinal cord and brain stem/medial lemniscus are not. This proposal requests support for measurement of the effect of analgesic agents, TE and/or morphine on somatosensory evoked potentials (SEP's) transduced from single recording electrodes in nociceptively responsive nuclei. Also, multi-electrode within the thalamus and somethetic cortex will allow the determination of sources of evoked electrical within these nuclear regions. These experiments will be conducted in anesthetized animals to minimize electrical background activity due to arousal. Recording sites for SEP's are taken from pilot studies, in which specific nuclear regions were found in the somatosensory cortex and thalamus where SEP responses to electric tail shock are significantly suppressed after TE treatment. The experiments will demonstrate the effects on nuclear SEP response by morphine, TE or both. Use of SEP suppression in target nuclei to demonstrate TE potentiation of morphine effects will yield additional information about the sites and mechanisms of TE. It also provides the necessary foundation for investigation of TE/morphine effects on SEP's in awake animals in which animal behavioral responses to increasing levels of tail shocks can be correlated with measurements of SEP suppression. This correlation may enable investigation of the use of combined TE and subclinical doses of morphine in pain relief therapy.