Veterinary Research Communications, 27 Suppl. 1 (2003) 745–748 © 2003 Kluwer Academic Publishers. Printed in the Netherlands
Brainstem Auditory Evoked-potentials in Dairy Cows Recorded with Nape-vertex Derivation M. Dondi*, E. Bianchi, D. Callegari and F. Quintavalla Animal Health Department, Section of Internal Medicine, Faculty of Veterinary Medicine, University of Parma, V ia del T aglio, 8, 43100 Parma, Italy *Correspondence: Dipartimento di Salute Animale, Sezione di Clinica Medica Veterinaria, Facolta` di Medicina Veterinaria, Universita` degli Studi di Parma, V ia del T aglio, 8, 43100 Parma, Italia E-mail:
[email protected] Keywords: BAEP, brainstem auditory-evoked potentials, cow
INTRODUCTION Brainstem auditory-evoked potentials (BAEP) are bioelectric waves that can be registered in the 10 ms following an auditory stimulus. Each electric potential, identified with consecutive Roman numerals, is generated by the activation of one of the subcortical components of the acoustic pathway. The BAEP test is used in the clinical diagnosis of hearing impairment (Kay et al., 1984) and in brainstem pathologies (Fischer and Obermaier, 1994). The BAEP trace can be registered from different points of the cranial region, but the most frequently used derivations position the electrodes behind the stimulated ear (Ai) and on the cranial vertex (Vertex). The possibility of applying the BAEP test in early diagnosis of CNS pathology in the cow is currently being studied. However, the use of this method for epidemiological studies in the field, on a large number of animals, would require several modifications in order to reduce manoeuvres and testing time, without losing test reliability. The aim of this work was to verify the efficacy of the BAEP test using a single derivation, with electrodes positioned at the Nape-Vertex.
MATERIALS AND METHODS Animals Five healthy dairy cows, aged 7–10 years, were used in the study. Cows were tested in the travail, without pharmacological containment, in a quiet room with a temperature of 20–25°C. 745
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Electrodes Teflon, monopolar needles 45 mm in length were used. The positive electrode was positioned along the median longitudinal line, half way between the nucal crest and the intercanthal line. The negative electrode was placed on the skin fold corresponding to the atlanto-epistropheal joint (Nape) and the ground electrode was positioned on the ventral margin of the ear. Each electrode was positioned in the sub-cutis using an 18-gauge butterfly needle as a guide. Stimulation Acoustic headphones were modified by attaching 5 cm long plastic conical tubes which were inserted into the ear canal. Auditory stimulation consisted of ‘alternate clicks’ with an intensity of 105 dB nHL and a frequency of 2 Hz. Contralateral masking was not used and the other ear was occluded by inserting a phonoabsorbent sponge into the external ear canal. Recording Two consecutive traces were recorded from each ear and calculated as the arithmetic mean of 1000 stimulations in order to verify the reliability of evoked potentials. Filters Filters were used for the high frequencies at 3000 Hz and for low frequencies at 100 Hz. Electroneurograph A Nihon Koden Four Mini, MEB 5304K instrument was used. Parameters Absolute latency for peaks (I; II; III; V) and relative latency (IPL) for I–V and II–V were measured. RESULTS AND CONCLUSIONS The BAEP traces obtained in this study on adult cows using our modified method were very similar to those obtained using the Ai-Vertex derivation (Strain et al., 1989).
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TABLE I Values for absolute and relative latencies (IPL). BAEP recorded in five cows aged 7–10 years, using unilateral acoustic stimulation of 105 dB intensity; I, II, III, V=waves numbers; L=left ear; R=right ear Cattle
Absolute waves latencies (ms)
IPL (ms)
ID name
Side
I
II
III
V
I–V
II–V
Cow 1
L R L R L R L R L R 1.55 0.07
1.62 1.42 1.46 1.64 1.52 1.58 1.56 1.57 1.54 1.54 2.33 0.08
2.25 2.18 2.29 2.48 2.42 2.31 2.34 2.37 2.34 2.33 3.85 0.11
3.88 3.82 3.92 3.94 3.80 3.76 3.68 3.70 3.98 3.97 4.84 0.07
4.76 4.82 4.94 4.86 4.82 4.86 4.92 4.92 4.78 4.76 3.30 0.10
3.14 3.40 3.48 3.22 3.30 3.28 3.36 3.35 3.24 3.22 2.52 0.09
2.50 2.64 2.65 2.48 2.40 2.54 2.58 2.55 2.44 2.43
Cow 2 Cow 3 Cow 4 Cow 5 Mean Standard dev.
Figure 1. BAEP trace using Nape-Vertex derivation following stimulation of the right ear in cow no. 2. Peaks I, II, II and V can be clearly seen and the reproducibility of the trace can be seen comparing the two consecutive recordings
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The values obtained from the BAEP traces are reported in Table I. All stimulated ears offered reproducible traces and it was consistently possible to identify waves I, II, III and V (see Figure 1). The delay/latency of these waves did not vary among tested animals and were comparable to results reported by other authors (Strain et al., 1989). In particular, inter-peak values I–V and II–V, which are little influenced by the nature of the stimulus (Chiappa, 1997) can be useful in the functional study of the brainstem. Advantages of our modified recording method over others described in the literature include ease of execution and rapidity. The use of a single derivation for the evaluation of both ears allows the operator to perform the examination without having to move the negative electrode between stimulation of one side and then the other. Therefore, the BAEP test performed as described by us is rapid, practical, sensitive and precise, all of which are necessary prerequisites for the application of this test on a large number of cattle, in difficult field conditions such as those found on dairy farms. REFERENCES Chiappa, K.H., 1997. Evoked Potentials in Clinical Medicine, 3rd edn, (Lippincott-Raven, Philadelphia), 157–197 Fischer, A. and Obermaier, G., 1994. Brainstem auditory-evoked potentials and neuropathologic correlates in 26 dogs with brain tumors. Journal of Veterinary Internal Medicine, 8, 363–369 Kay, R., Palmer, A.C. and Taylor, P.M., 1984. Hearing in the dog as assessed by auditory brainstem evoked potentials. T he Veterinary Record, 114, 81–84 Strain, G.M., Olcott, B.M., Thompson, D.R. and Graham, M.C., 1989. Brainstem auditory-evoked potentials in Holstein cows. Journal of Veterinary Internal Medicine, 3, 144–148
