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.     

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)     

Peaks of brainstem auditory evoked potentials in dogs

The effects of electrode configuration and click polarity on brainstem auditory evoked potentials (BAEP) in dogs were investigated to clarify the inconsistent nomenclature for each peak. Four positive peaks (waves 1, 2, 3 and 4) before a deep negative trough and a fifth positive peak (wave 5) following the trough were the basic components of BAEP in dogs, which were easily identified regardless of recording conditions such as electrode configuration and click polarity. Additional peaks tended to be present when a noncephalic reference electrode and/or single-polarity (rarefaction or condensation) click stimuli were used. The Roman nomenclature for the individual positive peaks of BAEP in dogs is confused owing to variations in the observed waveforms among researchers, but click polarity and/or reference electrode position can explain all the previously reported variations in BAEP waveforms in dogs. When the criteria concerning wave V in the guidelines of BAEP in human beings are applied to avoid further confusion of Roman nomenclature in dogs, it is recommended that the basic five positive peaks (waves 1, 2, 3, 4 and 5 as identified easily with Ai-Vertex configuration and alternating clicks) are designated as waves I, II, III, V and VI, respectively. Wave IV (wave 3b) occurs occasionally before wave V in dogs.Abbreviations BAEP brainstem auditory evoked potentials - dBHL dB hearing level - IPL interpeak latency - Ai the caudodorsal end of the zygomatic arch ipsilateral to the stimulated ear - Nape the neck over the spinous process of the fourth cervical vertebra     

Effects of heparin, citrate, and EDTA on plasma biochemistry of sheep: comparison with serum

This study was carried out to evaluate the features of neurological dysfunction in experimentally-induced bovine spongiform encephalopathy (BSE)-infected cattle using brainstem auditory evoked potentials (BAEP). The progressive prolongation of peak latency of waves III and V was observed right-and-left bilaterally at the onset of neurological symptoms. The peak latency of wave V and the I-V interpeak latency (IPL) in BSE cattle 22 and 24 months after intracerebral inoculation were significantly (P < 0.05) prolonged compared with the control cattle. In addition, the amplitude of the BAEP waves of the BSE cattle were low compared with the control cattle. Hearing loss occurred in the BSE cattle that showed advanced neurological symptoms such as tremor. It is thought that this BAEP data reflects a functional disorder in the central auditory nerve pathways characteristic of experimentally-induced BSE.     

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)     

Effect of dietary protein content on episodic growth hormone secretion and on heat production of male broiler chickens.

1. The effect of the crude protein content (200 and 150 g/kg) of isoenergetic diets on episodic growth hormone (GH) release and on heat production was investigated in male broiler chickens. 2. Decreasing the crude protein content of isoenergetic diets from 200 g/kg (HP diet) to 150 g/kg (LP diet) resulted in depressed body weight gain, impaired food conversion efficiency and increased abdominal fat deposition. 3. The pattern of growth hormone secretion was markedly affected by dietary treatment. Broiler chickens fed on the LP diet had higher overall mean, amplitude, baseline and peak frequency than the HP chickens. 4. The LP chickens produced more heat per unit of metabolic body weight than the HP chickens. 5. The hypothesis relating the pattern of GH secretion to protein conversion efficiency was corroborated.     

Visual evoked potentials in guinea pigs with brain lesion.

Visual evoked potentials (VEPs) were recorded in 10 adult male guinea pigs with brain lesion. Lesions were produced in 5 animals by superficial suction of the occipital lobe. The other 5 animals were orally administered with hexachlorophene (about 35 mg/kg/day) for 28 days. In the VEP following the ablation of the occipital lobe, the peaks P10, N20, P55, N75, N140 and P200 disappeared in many cases. The amplitude of the peak N40 decreased to approximately one half its control VEP. In the VEP obtained from the animals administered with hexachlorophene, the peak latencies of N20, P30, P55, N75 and P100 were slightly prolonged after the 7th day following the first administration. On the other hand, there was no change in the latency of N40 during the whole period of administration. The peak-to-peak amplitude showed some variability in different peaks. Histologically, diffuse status spongiosis were found in the white matter of the cerebrum, cerebellum, and brain stem. As described above, the ablation of the occipital lobe caused markedly depressed VEPs, however, the responses to the photic stimulation persisted after the injury. On the other hand, the VEPs of animals administered with hexachlorophene showed a high probability of peak appearance, and a decrease in amplitude was not marked.     

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.     

Electroretinogram and visual-evoked potential measurements in Holstein cows

The electroretinogram (ERG) and flash visual-evoked potential (FVEP) were recorded from 25 Holstein cows in a clinical setting without dark adaptation. Latencies to the a and b waves of the ERG were measured bilaterally. The ERG recordings were between the lower eyelid of the stimulated eye and the vertex, with ground on the nuchal crest. Stimuli for ERG and FVEP were 1.5 flashes of white light/s. Recorded ERG were highly consistent and repeatable. The average latencies for the a and b waves were 14 and 30 ms; the mean ab amplitude was 43 microV. The FVEP were recorded bilaterally between the middle of the interocular line and the midpoint of the nuchal crest, with ground on the vertex. The FVEP measurements included latencies to 5 alternating positive and negative peaks (P1, N1, P2, N2, and P3) and 4 peak-to-peak amplitudes (P1 to N1, N1 to P2, P2 to N2, and N2 to P3). The P2 peak was consistently the most prominent. Average latencies for the 5 peaks were 46, 64, 86, 106, and 137 ms for P1, N1, P2, N2, and P3, respectively. The FVEP peak-to-peak amplitudes had a high variability.     

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.     

Brain stem auditory potentials evoked by clicks in the presence of high-pass filtered noise in dogs

This study evaluates the effects of a high-frequency hearing loss simulated by the high-pass-noise masking method, on the click-evoked brain stem-evoked potentials (BAEP) characteristics in dogs. BAEP were obtained in response to rarefaction and condensation click stimuli from 60 dB normal hearing level (NHL, corresponding to 89 dB sound pressure level) to wave V threshold, using steps of 5 dB in eleven 58 to 80-day-old Beagle puppies. Responses were added, providing an equivalent to alternate polarity clicks, and subtracted, providing the rarefaction-condensation potential (RCDP). The procedure was repeated while constant level, high-pass filtered (HPF) noise was superposed to the click. Cut-off frequencies of the successively used filters were 8, 4, 2 and 1 kHz. For each condition, wave V and RCDP thresholds, and slope of the wave V latency-intensity curve (LIC) were collected. The intensity range at which RCDP could not be recorded (pre-RCDP range) was calculated. Compared with the no noise condition, the pre-RCDP range significantly diminished and the wave V threshold significantly increased when the superposed HPF noise reached the 4 kHz area. Wave V LIC slope became significantly steeper with the 2 kHz HPF noise. In this non-invasive model of high-frequency hearing loss, impaired hearing of frequencies from 8 kHz and above escaped detection through click BAEP study in dogs. Frequencies above 13 kHz were however not specifically addressed in this study.     

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.     

Relationship between latency of brainstem auditory‐evoked potentials and head size in dogs

Summary

Cranium and brainstem dimensions were measured in 32 postmortem dog heads. Positive correlations were found between cranium length (CL) and brainstem length (BL) (r=0.87), between cranium width (CW) and brainstem width (BW) (r=0.83), and between cranium distance (CD = CL CW/2) and brainstem distance (BD = BL+BW/2) (r=0.91). Positive correlation coefficients were also found between CL and CW (r=0.90), and between BL and BW (r=0.85). It was concluded that head size accurately reflected brainstem size. A least squares estimation of the brainstem distance (BD) from CL and CW values was BD = 10.9 + 0.16 (CL CW/2) (BD, CL and CW in mm).

Brainstem auditory evoked potentials (BAEPs) and cranium dimensions were measured in 43 dogs (86 ears) with different head size, body size, sex and age. Wave form, absolute and interpeak latencies and correlation coefficients, relating latencies to cranium dimensions and body weight, were analysed CL, CW, and CD were positively correlated with body weight (r=0.93, 0.70 and 0.93, respectively), and CL, CW, and CD were correlated with age (r=0.33, 0.52 and 0.40, respectively). BAEPs consisted of five distinct positive peaks (I to V). Secondary positive peaks following peaks I and II were seen in 60% (I') and 90% (II') of the recordings. Late waves were recorded in 90% (VI), 50% (VII), and 25% (VIII) of the recordings. Latencies increased with decreasing stimulus intensity level (from 90 dB to 10 dB hearing level, HL),especially for peaks I, II, V, and the I‐V interpeak interval Absolute and interpeak latencies were positively correlated with cranium distance and body weight. Correlation coefficients increased as wave latencies increased At 90 dB HL, the highest correlation coefficients, relating cranium distance to peak V and the I‐V interpeak latency, were 0.55 and 0.53 (P < 0.00001), respectively. Regression analysis showed that each 1 cm increase in cranium distance was accompanied by an increase of 0.006 ms in the latency of wave I, 0.03 ms for wave III, 0.05 ms for wave V, and 0.05 ms for the I‐V interpeak interval Regression analysis showed that an increase of 1 kg in body weight was accompanied by an increase of 0.001 ms in the latency of wave I, 0.005 ms for wave III, 0.011 ms for wave V, and 0.01 ms for the I‐V interpeak interval. It is concluded that head size, which accurately reflects brain size, is a relevant source (25%) of intersubject variance of BAEP latencies in the dog.     

Brainstem Auditory-Evoked Potentials in Holstein Cows

Brainstem auditory-evoked potentials (BAEP) were recorded from 29 Holstein cows in a typical clinical setting. The latencies of five positive peaks in the BAEP were measured, and latency-intensity functions were determined. The BAEP was similar to that reported in humans, dogs, horses, and other species. The responses were reproducible for each cow, with low variability between cows. Four peaks (I, II, III, V) were present in all recordings, and a fifth (IV) was present infrequently. All peak latencies decreased as click-stimulus intensity increased. The threshold for detection of the BAEP was higher than expected for the cow compared with the horse.     

Transcranial magnetic stimulation: normal values of magnetic motor evoked potentials in 84 normal horses and influence of height, weight, age and sex

REASONS FOR PERFORMING STUDY: Cervical spinal cord dysfunction is a common problem in equine medicine and the currently available tests give no objective information about the functionality of the nervous tracts. Therefore, transcranial magnetic stimulation (TMS) was performed in 84 healthy horses of different height in order to have an objective measure for the integrity of the descending motor tracts in normal horses. OBJECTIVES: To obtain reference values for onset latency and peak-to-peak amplitude of magnetic motor evoked potentials (MMEPs) and to evaluate the possible effect of height, age and gender on the neurophysiological measures. METHODS: All horses were sedated and stimulated transcranially by using a magnetic coil placed on the forehead. The stimulator triggered the sweep of an electromyogram machine that recorded MMEPs bilaterally from needle electrodes in the extensor carpi radialis and cranial tibial muscles. In that way, it was possible to measure latency between stimulus and onset of response. RESULTS: A significant difference was found between recordings made in the fore- and hindlimbs; MMEPs recorded in the front legs had a shorter onset latency and higher peak-to-peak amplitude. Mean +/- s.d. normal values for onset latency of 19.32 +/- 2.50 and 30.54 +/- 5.28 msecs and peak-to-peak amplitude values of 9.54 +/- 3.73 and 6.62 +/- 3.62 mV were obtained for extensor carpi radialis and cranial tibial muscles, respectively. The left-to-right difference in onset latency and peak-to-peak amplitude was not significant. In the same horse, differences up to 0.82 and 1.53 msecs for the extensor carpi radialis and cranial tibial muscles, respectively, lie within the 95% confidence limit and are considered normal. In contrast to onset latency, peak-to-peak amplitude showed a very large intra- and interindividual variability, even in the same muscle. To reduce the variability and predict normal values of new individual cases, influence of height, weight, age and sex on the MMEPs were determined. No significant effects of sex were observed on onset latency and peak-to-peak amplitude. The age of the horse had only a small but significant effect on peak-to-peak amplitude, with larger responses in older horses. Height at the withers and weight of the horse, parameters that strongly correlate with the size of the horse, had an important significant influence on onset latency but not on peak-to-peak amplitude. The age of the horse and height at the withers were used to predict peak-to-peak amplitude and onset latency, respectively, in normal horses. CONCLUSIONS AND POTENTIAL RELEVANCE: TMS is an excellent addition to the few tools we have for noninvasive imaging of the equine nervous system. Magnetically evoked potentials are highly reproducible and recent advances suggest that the applications of TMS in horses will continue to grow rapidly.     

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.     

Effect of dietary protein level on nitrogen metabolism in the growing bovine: I. Nitrogen recycling and intestinal protein supply in calves

Eight Angus heifer calves (234 kg) were assigned to either a high (HP; 126 g N/d) or low (LP; 66.5 g N/d) protein intake. Calves received 4.8 kg DM/d consisting of 30% cottonseed hulls and 70% corn-soybean meal in equal portions at 4-h intervals. Single doses of 14C- and 15N-urea and 15N-ammonium sulfate were injected into the blood urea-N (BUN) and ruminal NH3-N (RAN) pools, respectively, to measure rate of flux through, and transfer of N between, these and bacterial N. Nitrogen balance was greater (P less than .05) for HP than for LP (56.9 vs 25.1 g N/d), but abomasal N flow as a percentage of N intake was greater (P less than .05) for LP than for HP (124 vs 71.1%). Pool size and net synthesis rate for both RAN and BUN pools were greater (P less than .05) for HP than for LP. Calves fed HP degraded more (P less than .05) BUN in the gastrointestinal tract than calves fed LP (37.4 vs 14.0 g N/d). Quantities of RAN absorbed from the rumen also were greater (P less than .05) for HP than for LP (14.2 vs 2.8 g N/d). The proportion of total gastrointestinal BUN degradation occurring in the rumen averaged 53 and 26% for LP and HP. Data are interpreted to suggest that net incorporation of BUN into bacterial protein (urea recycling) is inversely related to level of protein intake.     

Brainstem auditory evoked potentials in Japanese Black and Holstein cattle

This study was performed to examine normal brainstem auditory evoked potential (BAEP) data for adult Japanese Black cattle and to evaluate whether differences exist in the peak latencies, interpeak latencies (IPL) and waveforms of BAEP between Japanese Black and Holstein cattle. The peaks were detected as major waves I, II, III and V in each group. The threshold of the BAEP waves in the Holstein cattle was 65-75 dB nHL, but the threshold in the Japanese Black cattle was 75-85 dB nHL. The I-III and I-V IPLs were significantly shorter in the Japanese Black compared with the Holstein cattle at an intensity of 105 dB nHL. The present findings suggest that the IPL and wave threshold of BAEP are influenced by bovine breed.     

Effects of dietary protein and growth hormone-releasing peptide (GHRP-2) on plasma IGF-1 and IGFBPs in Holstein steers

This study was conduct to determine the influence of dietary protein on the response of plasma insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding proteins (IGFBPs) to exogenous growth hormone releasing peptide-2 (GHRP-2 or KP 102) in Holstein steers. Eight 16-month-old Holstein steers were grouped by liveweight to two feeding treatments; high protein (HP; CP 1.38 kg/day and TDN 4.5 kg/day DM intake, n=4) or low protein (LP; CP 0.66 kg/day and TDN 4.42 kg/day DM intake, n=4). The experiment was a single reverse design whereby each group was injected twice daily with GHRP-2 (12.5 microg/kg body weight (BW)/day) or saline solution into the jugular vein for a 6-day period. Plasma IGF-1 in the HP group were higher than in the LP group (P<0.05), but plasma 34 kDa IGFBP-2 was lower in the HP than the LP group (P<0.05). The amplitude of the maximum growth hormone (GH) peaks responding to GHRP-2 injection were higher at day 1 than at day 6 of saline or GHRP-2 treatment in both LP and HP steers (P<0.05). The area under the GH response curve for 180 min after the GHRP-2 injection was not significantly different between the LP and the HP groups at days 1 and 6. A response in plasma IGF-1 concentration to GHRP-2 treatment in the HP group was observed at day 1 (198.9+/-18.1 ng/ml), day 2 (195.2+/-21.1 ng/ml) and day 6 (201.3+/-14.8 ng/ml) (P<0.05). No increase in plasma IGF-1 was observed from GHRP-2 administration in the LP group. Although the response of plasma IGF-1 concentration to GHRP-2 administration was increased in the HP group (P<0.05), there was no apparent effect of GHRP-2 treatment on plasma 38-43 kDa IGFBP-3 and 34 kDa IGFBP-2 at days 2 and 6 of treatment. In conclusion, it is proposed that the 34 kDa IGFBP-2 is sensitive to dietary protein level and may play an important role in the regulation of circulating IGF-1 in ruminant. In addition, increased plasma IGF-1 concentration observed in the HP group in response to the GHRP-2 treatment did not appear to affect plasma IGFBPs.     

A method of assessing auditory and brainstem function in horses

Brainstem auditory evoked potential (BAEP) waveforms were recorded as a means of objectively evaluating auditory and brainstem function in horses. BAEP recordings were readily and repeatably recorded from horses, under minimal restraint, using signal averaging equipment. Clearly identified BAEP waveforms were obtained with compression clicks of 30-100 dB (HHL) at 10 Hz applied in the external auditory meatus of one ear and masking white noise (10 dB lower) in the other ear. Vertex positive (upwards) waveforms I through V were obtained with an active, subdermal electrode over the ipsilateral and contralateral zygomatic processes of the temporal bones and the reference electrode over the vertex. Recording sweep duration was 10 ms, amplifier sensitivity 10 microV/division, display gain x 10 and low and high amplifier filters set at 200 Hz to 2 kHz. Such recordings can be useful in evaluation of all clinical cases suspected of showing degrees of deafness, vestibular disease or brainstem disease, and in monitoring the progress of such cases.