Lumbosacral spinal cord somatosensory evoked potentials for quantification of nociception in horses.

REASONS FOR PERFORMING STUDY: There is a need for objective evaluation and quantification of the efficacy of analgesic drugs and analgesic techniques in horses. OBJECTIVES: To determine whether lumbosacral spinal cord somatosensory evoked potentials (SSEP) can be a useful and reliable tool to assess nociception in equines. METHODS: SSEPs and electromyograms (EMG) from the epaxial muscles were recorded simultaneously, following electrical stimulation applied to the distal hindlimb in lightly anaesthetised Shetland ponies (n=7). In order to validate the model, the effect of increasing stimulus intensity was documented and the conduction velocities (CV) of the stimulated nerves were calculated. The effect of epidurally applied methadone (0.4 mg/kg bwt) in a randomised, crossover design was investigated. RESULTS: Two distinct complexes (N1P1 and N2P2) were identified in the SSEP waveform. Based on their latency and conduction velocity and the depressant effect of epidurally applied methadone, the SSEP N2P2 was ascribed to nociceptive Adelta-afferent stimulation. The SSEP N1P1 originated from non-nociceptive Abeta-afferent stimulation and was not influenced by epidurally applied methadone. CONCLUSIONS AND POTENTIAL RELEVANCE: The nociceptive Adelta component of the SSEP, the N2P2 complex, is presented as a valid and quantitative parameter of spinal nociceptive processing in the horse. Validation of the equine SSEP model enables the analgesic effects of new analgesics/analgesic techniques to be quantified and analgesia protocols for caudal epidural analgesia in equidae improved.

Sedative and cardiopulmonary effects of acepromazine, midazolam, butorphanol, acepromazine-butorphanol and midazolam-butorphanol on propofol anaesthesia in goats.

UNLABELLED: The sedative, propofol-sparing and cardiopulmonary effects of acepromazine, midazolam, butorphanol and combinations of butorphanol with acepromazine or midazolam in goats were evaluated. Six healthy Boer - Indigenous African crossbreed goats were by randomised cross-over designated to 6 groups: Group SAL that received saline, Group ACE that received acepromazine, Group MID that received midazolam, Group BUT that received butorphanol, Group ACEBUT that received acepromazine and butorphanol and Group MIDBUT that received midazolam and butorphanol as premedication agents intramuscularly on different occasions at least 3 weeks apart. The degree of sedation was assessed 20 minutes after administration of the premedication agents. Thirty minutes after premedication, the dose of propofol required for induction of anaesthesia adequate to allow placement of an endotracheal tube was determined. Cardiovascular, respiratory and arterial blood-gas parameters were assessed up to 30 minutes after induction of general anaesthesia. Acepromazine and midazolam produced significant sedation when administered alone, but premedication regimens incorporating butorphanol produced inconsistent results. The dose of propofol required for induction of anaesthesia was significantly reduced in goats that received midazolam alone, or midazolam combined with either acepromazine or butorphanol. The quality of induction of anaesthesia was good in all groups, including the control group. Cardiovascular, respiratory and blood-gas parameters were within normal limits in all groups and not significantly different between or within all groups. IN CONCLUSION: sedation with midazolam alone, or midazolam combined with either acepromazine or butorphanol significantly reduces the induction dose of propofol with minimal cardiopulmonary effects in goats.

The effects of buprenorphine on behaviour in the ACI and BN rat inbred strains.

Buprenorphine is a partial mu, kappa agonist that has been shown to influence spontaneous behaviour in animals. Previously, we have demonstrated significant differences in the analgesic response to buprenorphine between the August Copenhagen Irish (ACI)/SegHsd and the Brown Norway (BN)/RijHsd inbred rat strains. The purpose of this study was to determine whether these strains also differed in their behavioural response to buprenorphine in order to provide an additional parameter for the genetic analysis and localization of genes involved in this response. Male and female rats of both strains were used (n = 6/strain/sex) for this study. Each rat was subjected, respectively, to three treatment regimens at 15:00 h: (A) unchallenged; (B) intravenous saline; (C) intravenous buprenorphine (0.05 mg/kg) according to a crossover design. The relative duration (s/h) of locomotion, grooming, drinking and eating behaviour was subsequently determined from 15:30 to 07:00 h using the automatic registration system, Laboratory Animal Behaviour Registration and Analysis System(trade mark). Significant strain differences were observed in unchallenged behaviour between the ACI and the BN rats. ACI rats, but not BN rats, responded to buprenorphine treatment with decreased levels of locomotion, drinking and eating behaviour. The same treatment resulted in an increased grooming behaviour in both strains. Slight but significant sex differences were observed for locomotion and eating in the analysis of variance procedure, but did not reach the level of statistical significance in the multiple comparison procedure. The results of this study emphasize the possibility that strain-specific effects must be taken into account when using behavioural parameters for the assessment of the analgesic effects of buprenorphine in rats.

Application of a modified form of the Glasgow pain scale in a veterinary teaching centre in the Netherlands.

The Glasgow Composite Measure Pain Scale was developed to measure acute pain in dogs in a hospital setting. In this investigation a modified version of the scale was applied in a centre with a different surgical case load and analgesic protocols, and where English is not the first language, to test its validity in a different clinical environment. The modified scale was used to score pain in 60 dogs during the 24 hours after surgery. Their levels of sedation and a clinical impression of their pain were scored at the same time. Three questions were considered; first, how the modified pain score was related to the pain assessed subjectively, secondly, how it related to variables such as the surgical procedure and the dog's health and thirdly, how it changed over time. The mean modified pain scores for the dogs rated subjectively as having no, mild, moderate or severe pain were significantly different, indicating that the modified scale distinguished between pain of different severities. The changes in the dogs' scores also followed the expected changes in their level of pain with time, providing empirical evidence that the scale measures pain.

Differences in hepatic cytochrome P450 activity correlate with the strain-specific biotransformation of medetomidine in AX/JU and IIIVO/JU inbred rabbits.

Medetomidine is an alpha(2)-adrenoceptor agonist with sedative and analgesic properties. Previously we demonstrated significant differences in the response to medetomidine between two inbred rabbit strains, denoted IIIVO/JU and AX/JU. The aim of the present study was twofold: first, to compare the hepatic CYP450 enzyme activities between these rabbit strains [n = 13(male male,7 female female)/strain]. To this end, liver microsomes were incubated with known fluorescent substrates for the major drug-metabolizing CYP450 isoforms. A comparison of the obtained results indicated significant gender differences as well as differences between the two rabbit inbred strains. Secondly, the biotransformation rate of medetomidine in liver microsomes of both rabbit strains was determined using liquid chromatography coupled to tandem mass spectrometry. The rate of hydroxymedetomidine and medetomidine carboxylic acid formation was found to be significantly higher in the AX/JU strain. Specific CYP2D and CYP2E inhibitors could decrease the formation of both metabolites. Significant correlations were found between the rate of biotransformation of medetomidine and the activities of CYP2D and CYP2E, as well as between CYP450 enzyme activities and the anaesthetic response to medetomidine.

Differences in response to anaesthetics and analgesics between inbred rat strains.

Differences in response to analgesic and anaesthetic drugs can partly be attributed to variations in the genetic background of experimental animals. This study was carried out to determine differences in the response of inbred rat strains to a selection of analgesics and drugs used in anaesthetic protocols. A cross between the most contrasting strains can then be phenotyped in future studies in order to localize quantitative trait loci (QTLs) involved in analgesic/anaesthetic drug sensitivity. Eight inbred strains (n = 6 rats/strain) were selected for the study: the pigmented ACI, BN and COP strains and the albino F344, LEW, SHR, WAG and WKY strains. Each rat was injected intravenously with two analgesics (buprenorphine 0.05 mg/kg and nalbuphine 1 mg/kg) and three drugs used in anaesthetic protocols (propofol 25 mg/kg, medetomidine 50 microg/kg and ketamine 10 mg/kg), respectively, using a crossover design. Analgesic responses were assessed using an analgesiometric procedure. The sleep time of the rat and, where applicable, the interval between injection and loss of righting reflex were used to determine the anaesthetic response. Six out of eight strains responded significantly different from each other to the analgesic effect of buprenorphine with the ACI strain as hyper-responder. The tail withdrawal latency at 55 degrees C of the F344 and WKY rats using buprenorphine was not significantly different from baseline tail withdrawal latencies. In this study, all strains were non-responsive to the analgesic effects of nalbuphine. The response to all three drugs used in anaesthetic protocols differed significantly among the strains. The F344 and BN strains were relatively resistant to the sedative effects of medetomidine. Use of ketamine was abandoned in the ACI and BN strains when the first two animals of both strains died soon after induction. With all three drugs the sleep time of albino rats was significantly longer compared with that of the pigmented ones. We conclude that the results from this study can be used in future studies where QTLs for the sensitivity to anaesthetic/analgesic drugs are localized.

Validation of indicators used to assess unconsciousness in veal calves at slaughter.

European legislation states that after stunning regular checks should be performed to guarantee animals are unconscious between the end of the stunning process and death. When animals are killed without prior stunning these checks should be performed before the animal is released from restraint. The validity of certain indicators used to assess unconsciousness under different stunning and slaughter conditions is under debate. The aim of this study was to validate the absence of threat-, withdrawal-, corneal- and eyelid reflex as indicators to assess unconsciousness in calves subjected to different stunning and slaughter methods. Calves (201±22 kg) were randomly assigned to one of the following four treatments: (1) Captive bolt stunning followed by neck cut in an inverted position (n=25); (2) Non-stunned slaughter in an upright position (n=7); (3) Non-stunned slaughter in an inverted position (180° rotation) (n=25); (4) Non-stunned slaughter in an upright position followed by captive bolt stunning 40 s after the neck cut (n=25). Each calf was equipped with non-invasive electroencephalogram (EEG) electrodes before the slaughter procedure. All reflexes were verified once before the slaughter procedure. At the beginning of the procedure (T=0 s) calves were stunned (treatment 1) or neck cut in an upright position (treatment 2, 4) or inverted position (treatment 3). Calves of treatment 4 were captive bolt stunned 34±8 s after the neck cut. Reflexes were assessed every 20 s from T=15 s for all treatments until all reflex tests resulted in a negative response three times in a row and a flat line EEG was observed. In addition, reflexes were assessed 5 s after captive bolt stunning in calves of treatments 1 and 4. Visual assessment of changes in the amplitude and frequency of EEG traces was used to determine loss of consciousness. Timing of loss of consciousness was related to timing of loss of reflexes. After captive bolt stunning, absence of threat-, withdrawal-, corneal- and eyelid reflex indicated unconsciousness as determined by EEG recordings. After non-stunned slaughter, both threat- and withdrawal reflex were on average lost before calves were unconscious based on EEG recordings. The eyelid- and corneal reflex were on average lost after calves had lost consciousness based on EEG recordings and appeared to be distinctly conservative indicators of unconsciousness in non-stunned slaughtered calves since they were observed until 76±50 and 85±45 s (mean±SD), respectively, after EEG-based loss of consciousness.

Development of a rat model to assess the efficacy of the somatosensory-evoked potential as indicator of analgesia.

Drug-induced changes in somatosensory-evoked potentials (SEPs) are considered to reflect an altered nociceptive state. Therefore, the SEP is proposed to be a parameter of analgesic efficacy. However, at present, SEPs have not been studied in relation to animal pain. The present study aims to develop a rat model in which this relationship can be studied based on Pavlovian fear conditioning. Therefore, rats, implanted with epidural electro-encephalogram recording electrodes, were randomly assigned to either a paired or random-control group and subjected to an aversive-to-appetitive transfer paradigm. During the aversive phase, the SEP-stimulation paradigm (5 mA square wave pulses, n = 72, of 2 ms duration each, with a stimulus frequency of 0.5 Hz; total duration 144 s) was used as the unconditioned stimulus (US), while a tone (40 s, 1500 Hz, 85 dB sound pressure level) was used as the conditioned stimulus (CS). During the appetitive phase, the CS was presented paired to the presentation of a sugar pellet. When compared to the random-control group, the paired group showed significantly more freezing behavior and significantly less reward-directed behavior in response to the CS in the appetitive phase. In addition, SEPs were not significantly affected by fear conditioning. Based on these results, we conclude that the SEP-stimulation paradigm can be successfully employed as a US in fear conditioning. In future studies, fear conditioning can be carried out under different levels of an analgesic regimen to allow the changes in SEP parameters to be compared to changes in fear-induced behavior making this model potentially useful to validate SEP parameters as indicators of analgesia.

Clinical investigation of remifentanil and propofol for the total intravenous anaesthesia of dogs.

Fifteen adult dogs underwent elective ovariectomy. They were premedicated with 0.5 mg/kg methadone and 0.05 mg/kg(-1) atropine administered intramuscularly, and anaesthesia was induced with propofol and maintained with intravenous infusions of remifentanil at 0.6 microg/kg/minute and propofol; the mean (sd) rate of infusion of propofol throughout the period of anaesthesia was 0.33 (0.03) mg/kg/minute. The dogs were ventilated continuously with oxygen while they were anaesthetised. Their haemodynamic parameters were clinically acceptable during the period of anaesthesia. Two dogs received additional atropine to correct bradycardias of less than 60 bpm and several dogs received additional boluses of remifentanil or propofol to maintain an adequate depth of anaesthesia, as determined by a clinical assessment. The mean (range) time to the return of spontaneous respiration after stopping the remifentanil infusion was 11.1 (6.0 to 17.0) minutes, and the mean (range) time to the dogs standing was 38.0 (20.0 to 80.0) minutes. The quality of recovery was good in 12 of the dogs, two showed mild excitation in the immediate postoperative period and the other dog required additional analgesia with methadone.

Indicators used in livestock to assess unconsciousness after stunning: a review.

Assessing unconsciousness is important to safeguard animal welfare shortly after stunning at the slaughter plant. Indicators that can be visually evaluated are most often used when assessing unconsciousness, as they can be easily applied in slaughter plants. These indicators include reflexes originating from the brain stem (e.g. eye reflexes) or from the spinal cord (e.g. pedal reflex) and behavioural indicators such as loss of posture, vocalisations and rhythmic breathing. When physically stunning an animal, for example, captive bolt, most important indicators looked at are posture, righting reflex, rhythmic breathing and the corneal or palpebral reflex that should all be absent if the animal is unconscious. Spinal reflexes are difficult as a measure of unconsciousness with this type of stunning, as they may occur more vigorous. For stunning methods that do not physically destroy the brain, for example, electrical and gas stunning, most important indicators looked at are posture, righting reflex, natural blinking response, rhythmic breathing, vocalisations and focused eye movement that should all be absent if the animal is unconscious. Brain stem reflexes such as the cornea reflex are difficult as measures of unconsciousness in electrically stunned animals, as they may reflect residual brain stem activity and not necessarily consciousness. Under commercial conditions, none of the indicators mentioned above should be used as a single indicator to determine unconsciousness after stunning. Multiple indicators should be used to determine unconsciousness and sufficient time should be left for the animal to die following exsanguination before starting invasive dressing procedures such as scalding or skinning. The recording and subsequent assessment of brain activity, as presented in an electroencephalogram (EEG), is considered the most objective way to assess unconsciousness compared with reflexes and behavioural indicators, but is only applied in experimental set-ups. Studies performed in an experimental set-up have often looked at either the EEG or reflexes and behavioural indicators and there is a scarcity of studies that correlate these different readout parameters. It is recommended to study these correlations in more detail to investigate the validity of reflexes and behavioural indicators and to accurately determine the point in time at which the animal loses consciousness.

Validation of behavioural indicators used to assess unconsciousness in sheep.

The validity of behavioural indicators to assess unconsciousness under different slaughter conditions is under (inter)national debate. The aim of this study was to validate eyelid-, withdrawal-, threat reflex and rhythmic breathing as indicators to assess unconsciousness in sheep. Sheep were monitored during repeated propofol anaesthesia (n=12) and during non-stunned slaughter (n=22). Changes in the EEG and behavioural indices of consciousness/unconsciousness were assessed and compared in sheep. Threat reflex and rhythmic breathing correlated with EEG activity during propofol anaesthesia whilst absence of non-rhythmic breathing or threat reflex indicated unconsciousness. None of the behavioural indicators correlated with EEG activity during non-stunned slaughter. Absence of regular breathing and eyelid reflex was observed 00:27±00:12 min and 00:59±00:17 min (mean±SD) respectively after animals were considered unconscious, indicating that absence of regular breathing and eyelid reflex are distinctly conservative indicators of unconsciousness during non-stunned slaughter in sheep.

The rat vertex-middle latency auditory-evoked potential as indicator of anaesthetic depth: a comparison with evoked-reflex testing.

We investigated whether components from the rat Vx-MLAEP could be used to assess depth of anaesthesia induced by propofol. Propofol decreased MLAEP amplitudes and increased latencies. We propose that the P(16)-N(22) wave in the rat MLAEP is similar to the human P1, and that recovery of this wave during propofol anaesthesia correlates with behavioural measures of the regaining of consciousness.

Effect of arginine vasopressin on urine formation and plasma atrial natriuretic peptide level in conscious dogs.

We investigated the relationship between plasma arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) levels and urine formation in conscious dogs. The rate of urine production and urinary electrolyte excretion were determined following infusion of high doses of AVP to dogs in different volume states. Water deprivation for 24 h induced an antidiuresis while the plasma osmolality, plasma AVP and plasma ANP remained at physiological levels. Subsequent i.v. administration of AVP did not alter the production of urine. Oral water loading (20 ml/kg body weight) induced low plasma AVP levels (1.3 +/- 0.5 pg/ml, mean +/- S.E.M.). Following AVP administration to the water-loaded group, the urine production rate decreased significantly from baseline while the osmolality of the urine increased significantly. Plasma ANP levels did not differ significantly between the two experimental groups, and did not change following i.v. administration of AVP. The results show that, in conscious dogs, (1) the production of a small volume of highly concentrated urine can occur with plasma AVP levels of below 5 pg/ml, (2) 24 h of dehydration induces an antidiuresis while plasma peptides, as well as the different biochemical variables, remain within normal limits, (3) increased plasma AVP levels do not induce a change in plasma ANP levels under these experimental conditions, (4) infusion of AVP induces a significantly increased K+ excretion but only in overhydrated animals.

Effect of methadone on plasma arginine vasopressin level and urine production in conscious dogs.

The aim of this study was to examine the effect of i.v. methadone on the plasma arginine-vasopressin (AVP) levels and urine production in 9 conscious dogs. A highly significant increase from the baseline plasma AVP values of below 3 pg/ml occurred within 5 min following methadone administration. Maximum levels were reached within 30-50 min post-injection and varied from 18.5 to 100 pg/ml. A significant decrease in urine production was not seen under these experimental conditions. Mean arterial blood pressure did not change significantly during the experiment. Apart from the partial influence of the methadone-induced respiratory acidosis, we postulate a direct relationship between i.v. administration of methadone and the increased plasma AVP levels in dogs.

Effect of superior laryngeal nerve transection on pharyngeal muscle contraction timing and sequence of activity during eating and stimulation of the nucleus solitarius in dogs.

The effect of unilateral or bilateral transection of the superior laryngeal nerve on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in 10 dogs during eating and during unilateral electrical stimulation of the solitary nucleus. In all groups of dogs, after unilateral or bilateral transection, there were some swallowing actions in which the sequence of activity in the pharyngeal muscles was disturbed during eating and during stimulation of the solitary nucleus. In the dogs in which the transection was unilateral, this fraction was 18% in the ipsilateral muscles during eating and 7% in the contralateral muscles. After bilateral transection it was 8% in the left muscles and 16% in the right muscles. The fractions were not significantly different when swallowing was evoked by stimulation of the solitary nucleus. Swallowing actions having a normal sequence of activity in these dogs were compared with those in a group of eight dogs in which the superior laryngeal nerves were intact. Contraction timing was not significantly different during eating, but during stimulation of the solitary nucleus the timing was significantly shorter than in the dogs with intact nerves. It was concluded that superior laryngeal nerve transection modulates the central pattern generator for pharyngeal swallowing in dogs.

Effect of stimulating peripheral and central neural pathways on pharyngeal muscle contraction timing during swallowing in dogs.

The effect of stimulating peripheral and central neural pathways on the electromyographic activity in the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles was studied in eight dogs during 1) eating, 2) unilateral electrical stimulation of the superior laryngeal nerve, and 3) unilateral electrical stimulation of the solitary nucleus. The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the solitary nucleus in the anesthetized dog (mean difference 127 ms, SEM 9, n = 15). The duration of pharyngeal swallowing was significantly shorter during eating than during stimulation of the superior laryngeal nerve in the awake dog (mean difference 84 ms, SEM 13, n = 9). The duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve under anesthesia was significantly shorter than during stimulation of the solitary nucleus under anesthesia (mean difference 58 ms, SEM 18, n = 9). The difference in duration of pharyngeal swallowing during stimulation of the superior laryngeal nerve between the awake state and during anesthesia was not significant (mean 19 ms, SEM 14, n = 9). It was concluded that stimulation of peripheral and central neural pathways resulted in different pharyngeal muscle contraction timing during swallowing in dogs.

The humane collection of fetal bovine serum and possibilities for serum-free cell and tissue culture.

Fetal bovine serum (FBS) is a common supplement to in vitro culture media. A workshop was organized to discuss whether or not fetuses might suffer when blood is withdrawn, and to discuss serum replacement methods. When bovine fetuses are exposed after slaughter of the dam, they can suffer only if they inflate their lungs with air and increase their blood oxygen to levels compatible with awareness. Preventing fetuses from breathing air or killing them by an efficient method, according to clearly defined safeguards, ensures that fetal blood collection is humane. Since serum is a supplement of unknown composition, which could be contaminated with unwanted factors, there are scientific and safety reasons for omitting FBS from culture media. Several media have been developed in which minimal or no animal derived components are present. Also, different cell types have been adapted to serum-free media. As yet, no standard serum free media are present, and each cell type requires its own medium composition. Among other recommendations, the establishment of a public database with information on cell types and their serum-free medium composition is proposed.

Diffusion of n-butyl-p-aminobenzoate (BAB), lidocaine and bupivacaine through the human dura-arachnoid mater in vitro.

INTRODUCTION: Epidural administration of a suspension of n-butyl-p-aminobenzoate (BAB) to humans resulted in a selective, ultra-long lasting sensory block without motor function impairment. The absence of motor block was attributed to 'spatial' confinement of active concentrations of dissolved BAB within the epidural space. This study was designed to investigate the diffusion of BAB through the human dura-arachnoid membrane in vitro relative to lidocaine and bupivacaine and to quantify the influence of the composition of the suspension formulation on this flux. MATERIALS AND METHODS: Human dura-arachnoid specimens were mounted between the donor and the receiver compartment of a diffusion cell. Five concentrations of BAB, lidocaine and bupivacaine in phosphate-buffered saline, pH 7.4, were added to the donor compartment and the increase of the concentration of the agent in time in the receiver compartment was measured by automated UV-spectrometry. Fluxes and permeabilities were calculated. The influence of pH, polysorbate 80 (PS 80) and polyethylene glycol 3350 (PEG 3350) on the flux of BAB in solution and in suspension formulations were analyzed. RESULTS: The flux of both lidocaine and bupivacaine at pH 4 was considerably smaller than at pH 7.4. Permeabilities decreased in the order bupivacaine>lidocaine&z.Gt;BAB and at the level T12>T1. PS 80 at concentrations exceeding 0.025 mg/ml and PEG 3350 decreased the flux of BAB from BAB-solutions. Used in the preparation of the suspension, PS 80 and PEG 3350 did significantly reduce the permeability. DISCUSSION: The results of this study are consistent with the hypothesis that the selective action of epidurally applied BAB suspension can be attributed to the spatial confinement of active BAB-concentrations within the epidural space. Additives used in the preparation of the aqueous suspension formulation may substantially influence the local pharmacokinetics and by that the pharmacodynamic effects.

Middle-latency auditory-evoked potential in acepromazine-sedated dogs.

The middle-latency auditory-evoked potential (MLAEP) has been investigated as means of monitoring anesthesia in dogs. The goals of this study were to develop a technique to record MLAEPs in awake dogs and to determine the effects of sedation. The MLAEP was recorded in 12 dogs with and without sedation with acepromazine. Three needle electrodes were inserted SC. Click stimuli were delivered biaurally. Signal acquisition, averaging, and analysis were performed by software developed in-house. Signals were recorded for 128 milliseconds, and the responses to 1,024 stimuli were averaged. The waveforms from 10 recordings were averaged, and the amplitudes and latencies of peaks that could be consistently identified were measured. Data measured were compared by means of a paired 2-sided Student's t-test. Interpretable MLAEPs were recorded in 10 of the 12 dogs. Three peaks were consistently identified (Pa, Nb, and Pb). The latencies of these peaks were significantly (P = .032, .035, and .028, respectively) shorter in awake (mean +/- SD milliseconds) (Pa = 18.85 +/- 1.36, Nb = 30.50 +/- 3.55, and Pb = 47.70 +/- 5.53) than in sedated (Pa = 22.40 +/- 3.88, Nb = 35.75 +/- 6.77, and Pb = 55.30 +/- 10.55) dogs. The Pb amplitude was not significantly different (2.51 +/- 1.30 microV awake and 2.19 +/- 1.10 microV sedated). This study demonstrates that acepromazine sedation causes changes in MLAEP.