Subject
Male; Animals; Rats; Injections; Enkephalins/*pharmacology; Naloxone/pharmacology; Anesthetics/*pharmacology; Biogenic Monoamines/*physiology; Pain/*metabolism; Spinal Cord/drug effects/metabolism/*physiopathology; Dose-Response Relationship; Drug; Inbred Strains; Receptors; Enkephalin; Ala(2)-MePhe(4)-Gly(5)-; Spinal; 5)-; D-Penicillamine (2; Opioid/drug effects/*physiology; Enkephalins; Intraspinal; Amines – Physiology; Anesthetics – Pharmacodynamics; Cell Surface – Drug Effects; Cell Surface – Physiology; Enkephalins – Pharmacodynamics; Naloxone – Pharmacodynamics; Pain – Metabolism; Spinal Cord – Drug Effects; Spinal Cord – Metabolism; Spinal Cord – Physiopathology