Proposed Drug Combination A combination of medetomidine, ketamine, and buprenorphine (MKB) has been proposed for use in feral cat sterilization surgery. Similar to TKX, this combination of drugs is combined and administered intramuscularly as a single injection. Medetomidine and its specific antagonist, atipamezole, are highly specific for alpha adrenoceptors. Ketamine is classified as a dissociative anesthetic, offering a state of unconsciousness and somatic analgesia. Buprenorphine is an opioid analgesic used in pain management. It is hypothesized that the MKB combination may eliminate some of the inadequacies associated with TKX. Alpha2-Adrenoceptors Adrenergic drugs affect receptors stimulated by norepinephrine or epinephrine. These drugs can act directly on the receptor (adrenoceptor or adrenoreceptor) by activating it, blocking neurotransmitter actions, or interrupting the release of norepinephrine. Norepinephrine releasing neurons are found in the central and sympathetic nervous system where they serve as links between ganglia and effector organs (Howland & Mycek 2000). Adrenoceptors can be distinguished pharmacologically and are divided into two families, alpha (a) and beta (P). Alpha adrenoceptors are further subdivided into several classes, including alpha and alpha, based on relative affinities for agonists, independent of their anatomical location (Berthelsen & Pettinger 1977; Wickberg 1978; Wikberg 1978). Alpha2-adrenoceptors have been isolated in the central nervous system, gastrointestinal tract, uterus, kidney, and platelets and produce a variety of effects (Paddleford & Harvey 1999). Pharmacologic studies have revealed alpha2-adrenoceptors to be located in either pre-synaptic or post-synaptic positions (Cullen 1996). Alpha2-adrenoceptors located in the central nervous system regulate the neuronal release of norepinephrine and several other neurotransmitters that are intimately involved in the modulation of sympathetic outflow, cardiovascular and endocrine function, vigilance, emotion,