Effects of xylazine and ketamine on the acoustic reflex and brain stem auditory-evoked response in the cat

The acoustic reflex (AR) and brain stem auditory-evoked response (BAER) were recorded in adult cats 5 minutes after IM administration of xylazine (1 mg/kg) and after IM administration of ketamine (10 mg/kg). Ipsilateral and contralateral AR were recorded at 10 and 20 dB above acoustic reflex threshold 5 minutes after xylazine administration and 5 and 35 minutes after ketamine administration. Monaural BAER were recorded 5 minutes after xylazine and 5 and 35 minutes after ketamine, using stimulus intensities of 90-, 80-, and 70-dB hearing level (HL). Additional BAER were recorded at 10, 15, and 25 minutes after ketamine, using the 90-dB HL stimulus. Pre- and postinjection comparisons were made for threshold, latency, and amplitude of the AR and for latency and amplitude of waves I through VI of the BAER. At both stimulus intensities before and after ketamine administration threshold for the ipsilateral reflex was significantly lower (P greater than 0.05) than for the contralateral reflex. The threshold, latency, and amplitude of the AR were unaffected (P greater than 0.05) by the injection of ketamine after xylazine. The amplitude of BAER waves was not affected (P greater than 0.05) by ketamine after xylazine for each of the 3 stimulus intensities. Latency of the 90-dB HL-evoked response was increased (P less than or equal to 0.05) for waves III/IV at 5 and 35 minutes after ketamine, and for wave V at each of the postinjection times, except at postinjection minute 15.(ABSTRACT TRUNCATED AT 250 WORDS)     

Postnatal development of the brain stem auditory-evoked potential in dogs

Recordings of averaged brain stem auditory-evoked potentials were obtained from 13 Beagle pups of both genders to document the postnatal development of the response from age 1 to 76 days. Responses were recorded between needle electrodes placed on the vertex and the ipsilateral ear, with ground at the interorbital line. Recordings were performed without sedation. Low-amplitude responses to high-intensity stimuli could be recorded from animals prior to opening of the ear canals. Peak latencies did not change after day 20 for peak I, day 30 for peaks II and III, and day 40 for peak V. As a result, the interpeak latencies between peaks I and III did not change after day 30, but continued to decrease until day 40 for peaks III-V and I-V. Peak amplitudes reached plateau values by day 20 (peak I) or day 30 (peaks II, III, and V). All of the measured latency and amplitude values had significant (P less than 0.001) linear regression lines of latency vs age and amplitude vs age. The brain stem auditory-evoked potential thresholds were mature by day 20.     

Effects of analog filtering on brain stem auditory-evoked potentials in dogs.

Effects of analog filter frequency on brain stem auditory-evoked potentials (BAEP) were investigated in 7 non-sedated dogs. The BAEP were recorded successively at various low-pass (LP) and high-pass (HP) filter frequency settings. The analog filters had a rolloff of 6 dB/octave. Decrease of LP filter frequency from 30 kHz to 100 Hz caused prolongation of the peak latency and reduction of the peak-to-peak (from a positive peak to the following trough) and absolute (from a positive peak to the baseline) amplitudes for all peaks, except the peak latency for P5 and the absolute amplitude for P4. Changes in these variables were statistically significant (P less than 0.05) at different cutoff frequencies specific for the individual peaks. The interpeak latency between P1 and P4, and P4/P1 peak-to-peak amplitude ratio were not changed significantly. At the lowest LP filter frequency of 100 Hz, positive peaks (fast waves) seemed to be superimposed on a slow positive wave (slow wave). In contrast, increase of HP filter frequency from 0.53 to 160 Hz did not result in significant changes for any peaks, except for reduction in the absolute amplitude of P4. The various effects of LP filter frequency and negligible effects of HP filter frequency on individual peaks may be attributable to their frequency composition and/or elimination of the slow wave at higher HP filter frequency settings. On the basis of our results, LP filter setting of 3 kHz and HP filter setting of less than or equal to 53 Hz are recommended for recording of BAEP in dogs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pudendal reflexes and effects of conditioning stimuli in cats

Evaluation of pudendal reflexes and effects of pudendal branch conditioning on those reflexes was carried out in 2 studies. In the first study of pudendal reflexes, 20 adult male and female mixed-breed cats underwent surgical isolation of the anal branch, urethral branch, and distal trunk (consisting primarily of the dorsal nerve of the penis/clitoris) of the pudendal nerve. Reflexes were tested in all possible ipsilateral and contralateral test-response combinations. Latency values and effects of increasing stimulus rate on response amplitude were recorded. Reflexes were detected in all combinations, with response latencies between 6.3 and 13.0 ms. Response amplitudes were diminished at stimulus rates of 3 to 5 Hz, and responses were apparently abolished at 4 to 16 Hz, suggesting that pudendal reflexes are polysynaptic. In the second study of conditioning effects, 9 adult male and female mixed-breed cats underwent preparation similar to that for study 1. A train of conditioning stimuli was applied to branches of the pudendal nerve prior to attempting to induce reflex responses, as performed in study 1. Conditioning completely abolished reflex responses for a period of 70 to 130 ms. Reflex responses were diminished in amplitude, compared with those observed during preconditioning trials, for 180 to 300 ms after conditioning.     

Short latency auditory evoked potentials recorded from non-anaesthetized thoroughbred horses.

The Brainstem Auditory Evoked Potential (BAEP) is a recording of the electrical activity of the brainstem following an acoustic stimulation. Up to seven peaks may be identified within 10 ms, and are labelled I to VII. The first five of these peaks are of most clinical importance, and in normal horses, peaks I, III and V are always present at stimulus intensities of 70-100 dB. Repeated sampling of clinically normal subjects at different stimulus intensities has enabled mean latency values to be determined for the ipsilateral and contralateral peaks I, III and V, and also for the interpeak latencies (IPLs) at each intensity. The maximum, normal, absolute latency for ipsilateral peak I was 1.86 ms, for peak III, 3.53 ms and for peak V, 5.52 ms. The equivalent contralateral values were 2.50 ms, 4.44 ms and 5.59 ms. The maximum, normal, contralateral IPL for I-III was 1.78 ms, that for III-V was 2.26 ms and for I-V was 3.76 ms. The maximum, normal, contralateral IPLs were 2.17 ms for I-III, 1.41 ms for III-V and 3.32 ms for I-V. If a peak or peaks are absent or delayed, or the IPL is greater than expected, the patient can be determined to have abnormal brainstem or auditory nerve conduction. The amplitudes of peaks I and V were measured, and the ratio of amplitudes was determined, to find the normal V:I values. At a stimulus intensity of 100 dB, the ipsilateral ratio was 0.49 +/- 0.19, and the contralateral value 1.49 +/- 0.48. Dispersal values were also calculated, by dividing the height of the III-V complex by its duration. For a stimulus intensity of 100 dB, the ipsilateral dispersal value was 0.416 +/- 0.104 microV/ms, and the contralateral value of 0.473 +/- 0.074 microV/ms. A range of normal values for both V:I ratio and dispersal were calculated. Height, weight and inter-aural distance were measured, and the relationship of the various peaks and IPLs to these variables was ascertained by statistical analysis. For the ipsilateral values, the correlation between the latency of wave V, and III-V and I-V IPLs and weight were significant (P less than 0.01). Significant correlations were found between weight and the latency of contralateral waves III (P less than 0.05) and V (P less than 0.05) and the I-III (P less than 0.01) and I-V (P less than 0.001) IPLs.(ABSTRACT TRUNCATED AT 400 WORDS)     

Postnatal development of the visual-evoked potential in dogs

Recordings of visual-evoked potentials that were induced by flashes of white light were obtained from 13 Beagle pups to document the development of the response from age 7 to 100 days. Responses were recorded between needle electrodes placed on the nuchal crest and the interorbital line, with ground at the vertex. Five alternating positive (P) and negative (N) peaks were observed in most visual-evoked potentials: P1, N1, P2, N2, and P3. Responses were recorded from 2 pups prior to opening of the eyelids. Recordings were performed without sedation or dark adaptation. Peak latencies were essentially mature (equal to those of adult dogs) by day 11 for P1, and by day 38 for N1 and P2. The latencies to N2 and P3 did not reach adult values by day 100, but did reach plateau values by day 43. The P1-N1 amplitude measurements reached mature levels by day 14, whereas N1-P2 amplitudes were mature by day 32. The P2-N2 and N2-P3 amplitudes reached plateaus that greatly exceeded adult amplitudes by days 50 and 58, respectively. Maturation of visual-evoked potential responses paralleled reported morphologic development of the visual cortex. All of the measured latency and amplitude values had significant (P less than or equal to 0.004) linear regression lines of latency vs age or amplitude vs age.     

Measurement of anal and genitoanal reflexes in cats

Noninvasive determination of anal and genitoanal reflexes was evaluated in clinically normal cats. Thirty adult mixed-breed cats (15 sexually intact or castrated males, 15 sexually intact or spayed females) were sedated by IV administration of ketamine, acetylpromazine, and atropine. Anal reflexes were recorded from the anal sphincter muscle after ipsilateral and contralateral electrical stimulation of the perineal skin. Genitoanal reflexes were recorded from the anal sphincter muscle after electrical stimulation of the penis or clitoris. An anal sphincter response to tibial nerve stimulation was attempted. Anal reflexes from ipsilateral and contralateral stimulations and a genitoanal reflex were detected in all cats. Anal sphincter responses to tibial nerve stimulation were inconsistent (4/30) and were not included in any analyses. Anal reflexes had response latencies of 7.5 to 12.0 ms (ipsilateral stimulation) and 6.5 to 13 ms (contralateral stimulation). Genitoanal reflexes had latencies of 9.0 to 13.0 ms (males) and 6.5 to 9.0 ms (females). Anal reflex latencies were significantly (P less than 0.05) longer for contralateral, opposed to ipsilateral, stimulation and were significantly (P less than 0.05) longer in males than in females. Genitoanal reflex latencies were also significantly (P less than 0.05) longer in males than in females, reflecting the more peripheral stimulation site in males. Anal reflex responses could be recorded in 2 feline clinic patients with such severe perineal trauma that pudendal nerve function could not be manually evaluated A potentially favorable prognosis was given in each instance on the basis of detection of the response. One cat eventually recovered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cortical averaged evoked potentials produced by pudendal nerve stimulation in dogs

Averaged evoked potentials were recorded from the scalp of 22 dogs after repetitive stimulation of the pudendal nerve. Four experimental procedures were used: (1) percutaneous needle-stimulating electrodes with dogs tranquilized with xylazine; (2) percutaneous needle-stimulating electrodes with dogs tranquilized with acepromazine; (3) percutaneous needle-stimulating electrodes with dogs anesthetized with alpha-chloralose; and (4) Sherrington type stimulating electrodes applied directly to nerves with dogs anesthetized with alpha-chloralose. The average evoked potentials were similar with all treatments. Three peaks (N1, P1, and N2) with consistent latency and amplitude were generally present, followed by additional peaks with variable latencies and amplitudes. The mean latency for N1 after direct stimulation was significantly longer than the mean latency for N1 in the 3 other groups (95% confidence intervals). There were no other significant differences in mean latencies among groups for any of the peaks.     

Audiograms estimated from brainstem tone-evoked potentials in dogs from 10 days to 1.5 months of age

The objective of this study was to build audiograms from thresholds of brainstem tone-evoked potentials in dogs and to evaluate age-related change of the audiogram in puppies. Results were obtained from 9 Beagle puppies 10-47 days of age. Vertex to mastoid brainstem auditory-evoked potentials in response to 5.1-millisecond Hanning-gated sine waves with frequencies octave-spaced from 0.5 to 32 kHz were recorded. Three dogs were examined at 10, 13, 19, 25, and 45 days. Four other dogs were examined at 16 days. Data from 7 dogs between 42 and 47 days of age were pooled to obtain audiogram reference values in 1.5-month-old puppies. The best auditory threshold lowered from above 60 dB sound pressure level (SPL) to values close to 0 dB SPL between 13 and 25 days of age and then stabilized. The audible frequency range widened, including 32 kHz in all tested dogs from the 19th day. In the 7 1.5-month-old puppies, the mean auditory threshold decreased by 11 dB per octave from 0.5 to 2 kHz. The auditory threshold was lowest and held the same value from 2 to 8 kHz. The mean auditory threshold increased by 20 dB per octave from 8 to 32 kHz. Near threshold, click-evoked potentials test only a small part of the audible frequency range in dogs. Use of tone-evoked potentials may become a powerful tool in investigating dogs with possible partial hearing loss, including during the auditory system maturation period.     

Brain stem auditory-evoked potentials of dogs: wave forms and effects of recording electrode positions

Wave forms of canine brain stem auditory-evoked potentials (BAEP) and the effects of electrode positions on the wave forms were studied as a basis for experimental and clinical use of BAEP recording. The BAEP regularly consisted of 5 waves (I to V) with latencies and polarities similar to those of other species. In some dogs, waves II, III, and IV contained distinct subpeaks (a, b, c). Waves similar to waves VI and VII of other species were recorded in some dogs. With respect to BAEP, no site on the head was electrically inactive and BAEP could be recorded as far caudally as the caudal cervical region in some dogs. Wave I, positive in recordings from the dorsal midline of the calvaria (vertex) underwent polarity reversal and increased amplitude and duration in recordings made from caudal ventrolateral regions of the head (mastoid region). As a result, wave I partially or totally obscured wave II so that the latter could no longer be clearly identified. Waves IIIa and IIIb were differentially affected by moving the recording site, indicating that their generators were spatially separated. Waves IV and V were also affected by electrode site, consistent with previous reports that they have spatially separated generators in other species. In recordings made with vertex electrodes referenced to the mastoid region ipsilateral to the stimulated ear, wave I appeared as a high-amplitude positive peak with onset latency equalling that in noncephalic reference recordings, but with somewhat later peak latency and longer duration. As a result, wave II was partially or totally obscured so that only 4 major peaks were evident in the BAEP. In contralateral mastoid reference recordings, latency to peak of wave I was unchanged; however, amplitude of all waves was reduced and waves IIa and IIb were not as clearly differentiated as they were in noncephalic reference recordings.     

Thoracolaryngeal reflex latencies in Thoroughbred horses with recurrent laryngeal neuropathy

Electrolaryngeography was used to study the latencies of the thoracolaryngeal adductor reflex in Thoroughbred horses with and without recurrent laryngeal neuropathy (RLN). Latencies were compared in horses with grades 1 and 2 RLN, diagnosed by endoscopy in resting horses. The reliability of the measurements, effect of sedation and correlations of latencies with age of the horse were also studied. There was no effect of sedation on reflex latency periods. The latency of the reflex period measured to a convolved peak of the electromyographic response was significantly different in horses with grades 1 and 2 disease; medians and quartile ranges were 0.067 (0.065-0.073) and 0.072 (0.068-0.074) s, respectively (P<0.05). Significant associations were found between reflex latencies and both horse age and the grade of RLN. Reflex latency measurements are reliable and sensitive, and may assist with the clinical appraisal of Thoroughbred horses with RLN.     

Relative effects of xylazine-atropine, xylazine-atropine-ketamine, and xylazine-atropine-pentobarbital combinations and time-course effects of the latter two combinations on brain stem auditory-evoked potentials in dogs

Brain stem auditory-evoked potentials (BAEP) were recorded in 4 dogs to analyze the relationship between acoustic stimulus intensities and peak latencies of each wave, and to investigate the relative effects of xylazine-atropine, xylazine-atropine-ketamine, and xylazine-atropine-pentobarbital combinations and the time-course effects of the latter 2 drug combinations on BAEP. Click stimulations fixed at a stimulus rate of 10/s and a frequency of 4 kHz were delivered at intensities ranging from 10- to 110-dB sound pressure level (SPL) in 10-dB steps for analyzing the relationship between the acoustic stimulus intensities and the peak latencies and at an intensity of 110-dB SPL for investigating the effects of the sedative and anesthetic drug combinations and their time-course effects on BAEP. Waves I to VI were identified with stimulus intensity of greater than or equal to 50-dB SPL. Wave VII was observed in some records, but was excluded from statistical analysis. As stimulus intensity was increased from 50- to 110-dB SPL, the latency decreased for all waves during xylazine-atropine-ketamine anesthesia. There were no statistically significant differences in the peak latencies of each wave in BAEP among xylazine-atropine, xylazine-atropine-ketamine, and xylazine-atropine-pentobarbital combinations 20 minutes after drug administration, except that the latency of wave VI during xylazine-atropine sedation was significantly (P less than 0.01) shorter than that detected during xylazine-atropine-ketamine or xylazine-atropine-pentobarbital anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Click and low-, middle-, and high-frequency toneburst stimulation of the canine cochlea

A method was developed to deliver tonebursts ranging in frequency from 1 to 32 kHz for frequency-specific assessment of the canine cochlea. Brainstem auditory-evoked responses (early latency responses, 0-10 ms) to a click (CS) and to 1-, 2-, 4-, 8-, 12-, 16-, 24-, and 32-kHz toneburst stimulations (TS) were compared at 80-dB sound pressure level stimulus (SPL) intensity in 10 adult dogs. All stimulations yielded a 5-7 positive wave pattern, with the exception of the 1-kHz TS, which evoked a frequency-following response (FFR). Thresholds were lowest for the CS and the 12- and 16-kHz TS. All individual peak latencies for TS were significantly (P < or = .05) longer than for CS. Peak I latencies were significantly (P < or = .05) shorter for the 12- and 16-kHz TS than for the other TS. Interpeak latencies I-V were significantly (P < or = .05) longer for the 4- to 32-kHz TS than for CS. Differences in interpeak latencies I-III were not significant. Amplitudes of waves I and V were significantly (P < or = .05) lower for TS than for CS, except for higher wave V amplitude (P < or = .05) at 2- and 32-kHz TS. Peak I-V amplitude ratios were significantly (P < or = .05) higher for the 2-, 4-, 16-, 24-, and 32-kHz TS and lower for the 8- and 12-kHz TS, compared to CS. We conclude that reproducible information on frequency specificity of the canine cochlea can be obtained by TS. This report provides a normative database for parameters needed to evaluate frequency-specific hearing loss in dogs.     

Postnatal Development of Brainstem Auditory-Evoked Potentials, Electroretinograms, and Visual-Evoked Potentials in the Calf

Brainstem auditory-evoked potentials (BAEP), electroretinograms (ERG), and visual-evoked potentials (VEP) were recorded for eight calves from birth to 56 days and the values compared with previously determined adult responses. The BAEPs, ERGs, and VEPs recorded within the first 24 hours after birth contained all of the peaks seen in adult recordings. Varying degrees of maturation of the responses were documented as changes in latency and amplitude with age. The BAEPs were adult-like at birth, with latencies falling within the mean, plus or minus one standard deviation, for adult cows. A small but significant decrease in latency with age was seen for the first, second, and fourth peaks of the response. The ERG amplitudes were also within the adult range for the entire period of the study. Latencies to the a- and b-waves declined during the first 14 days and then stabilized at adult values. The VEP latencies decreased with age, with late peaks changing more than early peaks. Latencies of all but the first peak decreased to values less than the adult range. Two VEP amplitudes increased significantly with age. Developmental appears in the calf and other precocious species are compared to those in altricious (nonprecocious) species.     

Changes in oscillatory potentials in the canine electroretinogram during dark adaptation

Oscillatory potentials (OP) and electroretinograms (ERG) were recorded from clinically normal dogs after 5, 10, 15, 20, 30, 40, 50, and 60 minutes of dark adaptation. At the end of the adaptation period, OP were characterized by 5 distinct positive peaks, O1 through O5, with mean latencies of 14.46, 20.24, 27.38, 35.31, and 44.85 ms, respectively, and with mean amplitudes ranging from 7.20 to 34.84 microV. After 60 minutes of dark adaptation, the ERG had a mean a-wave latency of 12.03 ms and a mean b-wave amplitude of 109.29 microV. Peaks O3 and O4, which partially mask the summit of the b-wave, had mean latencies of 28.66 and 36.83 ms, respectively. The mean amplitude of the b-wave measured to the peak of O3 was 240.06 microV and 230.73 microV when measured to peak O4. Changes in the OP during dark adaptation consisted of significant (P less than 0.05) increases in the latencies of O1, O2, and O3, and significant increases in the amplitudes of O1, O3, O4, and O5. Concurrent ERG changes consisted of significant increases in the amplitudes of the a-wave and b-wave measured from O3 and O4, and significant increases in the latencies of peaks O3 and O4 on the b-wave.     

Measurement of the Lateral Thoracic Reflex Latency in Ponies

Lateral thoracic nerve reflex latencies values were measured in ponies using a simple, non-invasive technique. The reflex was elicited using an external triggering hammer attached to an electrodiagnostic unit. The resulting evoked, compound muscle action potentials were recorded with electrodes, which were placed over the 6th ribs or 11th rib level with the axilla. Two superimposed repeats of 4 signal-averaged sweeps of 50 or 100 milliseconds were recorded and the estimated reflex pathway was measured for each subject in order to calculate the reflex latencies and latency velocities. Mean left and right 6th rib peak latencies were not significantly different from each other ( P = .609), but left 6th rib latencies were shorter than those recorded from the 11th rib ( P < .0001), substantiating the existence of an indirect (central) pathway to the reflex. The calculated left and right 6th rib latency velocities were not significantly different from each other ( P = .58) but left 6th rib latency velocities were different from left 11th rib ( P = .009). The calculated latency velocities were within the broad range for corticospinal tract motor conduction velocities and comparable to magnetic motor evoked latency velocities. The use of lateral thoracic reflex latency measurements to objectively identify the site of spinal cord lesions is discussed.     

Early auditory evoked potentials (EAEPs) for the clinical diagnosis of otitis media in the rabbit

The main objectives of the study presented here were to prove the early auditory evoked potentials (EAEPs) as an objective procedure to confirm the diagnosis of otitis media in the rabbit. Therefore, in a clinical study the latencies and amplitudes of the EAEPs of 67 (ear) healthy rabbits were determined at sound pressure levels (SPLs) of 80, 60 and 40 dB. In comparison, the EAEPs of 9 rabbits with otitis media/interna were measured and the deviation of the latencies and amplitudes statistically analysed. The rabbits (no clinical signs of ear disease) showed at 80 dB SPLs the following latencies: potential 0 appeared with 0.53 ms (= average latency, +/- 0.12 ms standard deviation), potential I with an average latency from 1.26 (+/- 0.13) ms, potential II with 2.04 (+/- 0.14) ms, potential III with 2.71 (+/- 0.13) ms, potential IV with 3.72 (+/- 0.17) ms and potential V, which often was difficult to recognize, had an average latency of 4.62 (+/- 0.30) ms. In comparison to these results the rabbits with otitis media showed significant longer latencies at a sound pressure level of 80 dB for potential II, III and IV. Altogether, all mean values of latencies were prolonged in the affected rabbits. The amplitudes of the potentials of the rabbits without clinical signs of ear disease had a broad mean variation with large individual differences. The comparison of the results of EAEPs between rabbits with and without otitis media showed some differences of the latencies but these differences were not obviously enough to confirm the diagnosis of otitis media. Overall, the results showed that EAEPs with only three different sound pressure levels give no convincing results, although extensively prolonged latencies could lead suspicion on the diagnosis of otitis media. Further studies about the ascertainment of the objectively acoustic threshold in the rabbit with otitis media are necessary. The comparison of the latencies and amplitudes in the EAEPs between male and female rabbits showed longer latencies of potential III for male rabbits at 80 and 60 dB SPLs. Furthermore the results of latencies and amplitudes were compared between dwarf rabbits and other breeds. In dwarf rabbits (with an average body weight of 1420 g) significant higher amplitudes for the potentials I, II, IV and V were detectable than in other breeds (with an average body weight of 2852 g). This can be due to different body mass or different headsize.     

Changes in the visual evoked potentials with different photic conditions in guinea pigs.

Visual evoked potential (VEP) was studied in five adult male guinea pigs weighing 350-750 g. VEPs were recorded with chronically implanted electrodes. Photic stimulation was presented in the following order: binocular, left eye, right eye, and screened binocular. The averages of the responses were made from 140 samples. When a single eye was exposed to photic stimulation, the ipsilateral VEP was different from the contralateral VEP; the peaks N140 and P200 disappeared, and the peak latencies of N75 and P100 were significantly (P less than 0.05) longer than those in the contralateral hemisphere. Peak-to-peak amplitude N40-P55 in the ipsilateral VEP was significantly (P less than 0.05) lower than that in the contralateral VEP. The contralateral VEP by monocular stimulation was generally indistinguishable from the response to binocular stimulation. As described above, when only a single eye was exposed to flashes, the ipsilateral dural VEP was different from the contralateral dural VEP.     

Brain stem auditory-evoked responses in the dog

Brain stem auditory-evoked responses (BAER) were recorded from 58 dogs that did not have a known history of hearing problems. The BAER wave forms had an overall mean amplitude approximately 3.0 microV and typically consisted of a series of 4 to 5 vertex-positive peaks (peaks I through V). When acoustic clicks having intensities of 60-dB hearing level (decibels relative to the subjective hearing threshold) were used as stimuli, peak I had a latency of 1.49 +/- 0.13 ms; peak II, 2.32 +/- 0.14 ms; peak III, 3.01 +/- 0.25 ms; peak IV, 4.22 +/- 0.27 ms; and peak V, 5.55 +/- 0.37 ms. Latency values were influenced by a number of nonpathologic factors, including stimulus intensity and the body temperature of the dog. As stimulus intensity was decreased, there was a lengthening of the latency of each peak coupled with a decrease in the overall amplitude of BAER. Decreases in rectal temperature caused a similar lengthening of peak latencies. Age may have an influence on BAER, but under the conditions of the present study, the effect was not significant.     

Nature of the late potentials and F-ratio values in dogs

There is controversy about the nature of the late potentials (F-waves and H-reflexes) in dogs. This work has attempted to clarify the problem by comparing late potentials in eight intact and four chronically deafferented dogs. Pure H-reflexes were recorded inconsistently from intact preparations at voltages below the threshold for the M-wave. At stimulation voltages giving maximum direct responses, there was no statistically significant difference between the amplitude and latency of the late potentials of the two groups. However, there was a tendency for the late potentials to be of larger amplitude and longer duration in intact preparations. Late potentials in intact preparations had a composite waveform consisting of both F-waves and H-reflex components. F-waves only were present in deafferented limbs, and their amplitude was proportional to the intensity of the stimulus. F-ratios could be calculated by using the latencies of the late potentials, because the F-wave did not have a longer latency than the H-reflex. The following reference values for the F-ratio are proposed: 1.954 +/- 0.086 when stimulating at the hock and 0.883 +/- 0.052 when stimulating at the popliteal fossa.