Modulation of nociceptive withdrawal reflexes evoked by single and repeated nociceptive stimuli in conscious dogs by low-dose acepromazine.
OBJECTIVE
To investigate the modulation of the nociceptive withdrawal reflex (NWR) and temporal summation (TS) by low-dose acepromazine (ACP) in conscious dogs. To assess the short- and long-term stability of the reflex thresholds.


METHODS
Randomized, blinded, placebo-controlled cross-over experimental study.


METHODS
Eight adult male Beagles.


METHODS
The NWR was elicited using single transcutaneous electrical stimulation of the ulnar nerve. Repeated stimuli (10 pulses, 5 Hz) were applied to evoke TS. The responses of the deltoideus muscle were recorded and quantified by surface electromyography and the behavioural reactions were scored. Each dog received 0.01 mg kg(-1) ACP or an equal volume saline intravenously (IV) at 1 week intervals. Measurements were performed before (baseline) and 20, 60 and 100 minutes after drug administration. Sedation was scored before drug administration and then at 10 minutes intervals. Data were analyzed with Friedman repeated measures analysis of variance on ranks and Wilcoxon signed rank tests.


RESULTS
Acepromazine resulted in a mild tranquilization becoming obvious at 20 minutes and peaking 30 minutes after injection. Single (I(t)) and repeated stimuli (TS(t)) threshold intensities, NWR and TS characteristics and behavioural responses were not affected by the ACP at any time point. Both I(t) and TS(t) were stable over time.


CONCLUSIONS
In dogs, 0.01 mg kg(-1) ACP IV had no modulatory action on the NWR evoked by single or repeated stimuli, suggesting no antinociceptive activity on phasic nociceptive stimuli. The evidence of the stability of the NWR thresholds supports the use of the model as an objective tool to investigate nociception in conscious dogs. A low dose of ACP administered as the sole drug, can be used to facilitate the recordings in anxious subjects without altering the validity of this model.
Bergadano
Alessandra
A
Department of Clinical Veterinary Medicine, University of Berne, Switzerland. alessandra.bergadano@knp.unibe.ch
Andersen
Ole K
OK
Arendt-Nielsen
Lars
L
Spadavecchia
Claudia
C
D000075:Acepromazine / Q000008:administration & dosage* / Q000494:pharmacology*; D000818:Animals; D018592:Cross-Over Studies; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D008297:Male; D010146:Pain / Q000662:veterinary*; D017288:Pain Threshold / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects*; D014149:Tranquilizing Agents / Q000008:administration & dosage / Q000494:pharmacology
D014149:Tranquilizing Agents; D000075:Acepromazine