Inefficiency of bilateral amygdaloid lesions to reduce the transient motor reactions exhibited by swine during exposure to CO₂

The aim of the study was to evaluate from the ethical point of view the importance of transient muscular jerks commonly exhibited by swine at an early stage of pre‐slaughter CO₂ anaesthesia. The influence of 5 min restraint upon plasma concentrations of adrenaline (A) and noradrenaline (NA) was studied in swine (n= 6) before and after bilateral lesioning of the amygdaloid region of the brain, as were the motor reactions of the same and three other animals during 1 min exposure to 80% CO₂. The A and NA responses to the restraint became almost extinguished after amygdaloid lesioning in three of the animals, were reduced by about 50% in one swine, whereas no reduction was seen in the other two animals investigated. The amygdaloid lesioning did not visibly influence the latency for, and the duration and intensity of the muscular jerks manifested by the swine during the CO₂‐exposure. The results do not favour the possibility that transient motor reactions exhibited by swine during pre‐slaughter CO₂‐exposure are manifestations of emotional stress. Instead, the study indirectly supports the idea that the cause of the muscular jerks may be disinhibition of subcortical motor centres being inactivated by the CO₂‐anaesthesia somewhat later than neocortical cells normally exerting the inhibition.