title: The information transmitted by ensembles of primary spindle afferents is diminished when ketamine is used as a pre-anaesthetic.
abstract: The effect of pre-anaesthetic ketamine on ensemble coding of different stimuli consisting of muscle stretches of various amplitudes was studied for ensembles of simultaneously recorded primary muscle spindle afferents (MSAs). The experiments were conducted on 8 alpha-chloralose anaesthetised cats. Three of the cats received a pre-anaesthetic dose of ketamine (25 mg/kg) injected subcutaneously (ketamine group), while the remaining five animals did not (non-ketamine group). Data for ensemble coding were collected both before and after cutting the ventral root. A method based on principal component analysis and algorithms was used to quantify stimulus discrimination and an ANOVA tested differences between groups as well as differences due to ventral root cutting. When the fusimotor supply was intact, a general trend of an increase in the ability to discriminate stimuli with increasing ensemble size was observed for both groups, however, this trend was significantly greater for the non-ketamine group as compared to the ketamine group. When the ventral root was cut, the discrimination pattern for the non-ketamine group decreased significantly (as compared to before ventral root cutting), however, no change occurred for the ketamine group. Consequently, no difference in discrimination pattern was detected between groups after ventral root cutting. The reduction in information transmitted by ensembles of primary MSAs when ketamine is used as a pre-anaesthetic may suggest that ketamine elicits an adverse affect on the fusimotor system.
authors.affiliation: Department of Musculoskeletal Research, National Institute for Working Life, Umeå, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Bergenheim
authors.forename: A G
authors.initials: AG
authors.lastname: Crenshaw
authors.forename: J
authors.initials: J
authors.lastname: Pedersen
authors.forename: H
authors.initials: H
authors.lastname: Johansson
mesh_terms: D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology*; D000465:Algorithms; D000704:Analysis of Variance; D000768:Anesthesia, General; D000778:Anesthetics, Dissociative / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D002698:Chloralose; D004558:Electric Stimulation; D007649:Ketamine / Q000008:administration & dosage / Q000494:pharmacology*; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D011292:Premedication
chemical_list: D000778:Anesthetics, Dissociative; D002698:Chloralose; D007649:Ketamine