NOCICEPTIVE RESPONSES OF GUINEA-PIGS TO INTRADERMAL INJECTIONS OF BRADYKININ AND KALLIDIN-10

Evaluation of Using Behavioural Changes to Assess Post-Operative Pain in the Guinea Pig (Cavia porcellus)

To manage pain effectively in people and animals, it is essential to recognise when pain is present and to assess its intensity. Currently there is very little information regarding the signs of post-surgical pain or its management in guinea pigs. Studies from other rodent species indicate that behaviour-based scoring systems can be used successfully to detect pain and evaluate analgesic efficacy. This preliminary study aimed to establish whether behaviour-based scoring systems could be developed to assess post-surgical pain in guinea pigs. This prospective, randomised, placebo-controlled study used 16 guinea pigs, and evaluated changes in behaviour following either anaesthesia alone or anaesthesia and orchiectomy. Behaviour was assessed using a combination of manual and automated scoring of remotely obtained video footage. A small number of behaviours were identified that appeared to have high specificity for pain caused by orchiectomy. However, the behaviours were displayed infrequently. The most common was a change in posture from standing to recumbency, sometimes with one hind leg extended either to the side or behind the body. A composite behaviour score incorporating these abnormal behaviours differentiated between the effects of surgery and anaesthesia alone (p<0.0001), and between animals that received analgesia post-operatively compared to an untreated group (p<0.0001). Although behavioural changes occurred in these guinea pigs after orchiectomy, the changes were relatively subtle and the individual specific pain-related behaviours occurred infrequently. However, it may prove possible to develop a behaviour-based scoring system for routine use in this species using a combination of pain-related behaviours.

Nervous outflow from skeletal muscle following chemical noxious stimulation

1. In order to determine the nervous outflow from skeletal muscle during chemically induced muscle pain, the impulse activity of various types of muscle afferents in response to close intra-arterial injections of pain-producing substances (bradykinin, 5-hydroxytryptamine, histamine and potassium) was studied in anaesthetized cats using a single fibre recording technique.2. By administration of algesic agents in doses which produce pain in man and pain reactions in animals, about half of the group IV and two thirds of the group III muscle afferents could be activated. In contrast, group II and group I afferent units were usually not excited by chemical noxious stimulation. If effects at all occurred in the thick myelinated afferents, they consisted of a depression of the fibre activity rather than of an activation.3. The qualitative features of the discharges of group III muscle afferents induced by chemical stimulation resembled those of the group IV units very closely. The group III units differed from the group IV afferents in that their responses to a given dose of bradykinin were of greater magnitude.4. It is concluded that the chemically induced muscle pain is probably mediated by certain portions of the group IV and group III afferents, whereas the reactions of group II and group I units to algesic agents are such that a contribution to muscular chemo-nociception seems improbable.

Codeine and its alternates for pain and cough relief. I. Codeine, exclusive of its antitussive action

This report-the first of a series on codeine and its alternates for pain and cough relief-presents a detailed evaluation of experimental and clinical data concerning the analgesic action of codeine (the antitussive action will be assessed separately). The authors discuss the pharmacology of the drug, including side-effects and toxicity; effects on the respiratory, circulatory, digestive and urinary systems; tolerance, dependence and liability to abuse; metabolic effects; and mechanism of action.Though codeine is generally more toxic than morphine to animals on account of its convulsant action, it is less toxic to man, possibly because it produces less respiratory depression. Again, tolerance to its analgesic effects has been demonstrated in several animal species, but dependence in man is observed far less frequently than it is with morphine, and the abstinence syndrome is less intense. From their extensive review of the evidence available, the authors conclude that codeine is a good analgesic and that little risk to public health is likely to arise from its clinical use to relieve pain.