Effect of hyperbaric oxygen on lipid peroxidation in free skin grafts in rats.

OBJECTIVE: To document that free skin grafts treated with hyperbaric oxygen (HBO) are at greater risk for reperfusion injury, resulting in lipid peroxidation, than are free skin grafts without HBO treatment. ANIMALS: 40 Sprague-Dawley rats. PROCEDURE: Free skin grafting was performed bilaterally on each rat. The HBO-treated rats received HBO twice daily for 90 minutes at 2 ATA. Biopsy specimens were taken from each rat at the time of grafting and on days 2, 4, 7, 10, 14, 21, and 28, then were processed for tissue concentration of total glutathione (GSHt), glutathione peroxidase activity (GPx), and presence of thiobarbituric acid-reactive substances (TBARS). RESULTS: Both groups had a similar pattern of change in TBARS and GPx values--initial increase, returning to preoperative values at days 21 (control) and 28 (HBO). The GPx activity peaked later than did TBARS concentration (day 7 vs day 4). The pattern was significantly more pronounced in HBO-treated than in control rats. Both groups had a similar pattern of change in GSHt values-significant decrease from preoperative concentration at day 2, return to preoperative concentration by days 4 (HBO) and 7 (control), increase above preoperative concentration by day 21, and return to preoperative concentration by day 28. Obvious visual or histologic differences in the grafts were not detected between groups. CONCLUSIONS: Cellular effects of oxidative stress were apparent in both groups of rats; however, the degree of these effects was exacerbated by HBO. In the face of enhanced cellular lipid peroxidation, use of HBO for the treatment of free skin grafts must be questioned.

Air- and bone-conduction brainstem auditory evoked potentials and flash visual evoked potentials in cats.

OBJECTIVE: To document normal values for air- and bone-conducted brainstem auditory evoked potentials (BAEP) and for flash visual evoked potentials (VEP) in cats. ANIMALS: 10 mixed-breed cats (5 males) with normal physical, neurologic, otoscopic, and funduscopic examination results. PROCEDURE: BAEP in response to air- and bone-conducted click stimuli and VEP in response to flash stimuli were recorded to document species normative data. Mean and SD values were calculated for amplitudes and latencies of 4 peaks in the BAEP in response to air- and bone-conducted stimuli, and for latencies to 5 peaks and the 4 associated peak-to-peak amplitudes in the VEP. RESULTS: BAEP peak latencies increased and peak amplitudes decreased with decreasing stimulus intensity. Latencies were shorter for bone-conducted stimuli owing to the shorter transit time to the cochlea through bone, compared with air, but there were no differences for interpeak latencies. The BAEP and VEP recordings were similar to those reported for cats in other reports and were similar to those seen in other species. CLINICAL RELEVANCE: Normative data will permit performance of noninvasive electrodiagnostic evaluation of feline auditory and visual systems.

Ototoxicity assessment of a gentamicin sulfate otic preparation in dogs.

Vestibulotoxic and ototoxic effects often are seen after long-term, high-dose systemic treatment with gentamicin, but toxic effects after topical use have not been reported in animals, to the authors' knowledge. Vestibular and auditory effects of twice daily otic gentamicin treatment for 21 days were evaluated in 10 dogs with intact tympanic membranes and in the same 10 dogs after experimental bilateral myringotomy. Each dog served as its own control; 7 drops of gentamicin sulfate (3 mg/ml in a buffered aqueous vehicle) were placed in 1 ear, and 7 drops of vehicle were placed in the opposite ear. Treatment and control ears were reversed after myringotomy. Vestibular function was evaluated daily by neurologic examination and behavioral assessment. Auditory function was evaluated twice weekly by determination of brain stem auditory evoked potentials. Gentamicin sulfate placed in the ear of clinically normal dogs with intact or ruptured tympanic membranes, in the quantities used in this study, did not induce detectable alteration of cochlear or vestibular function. Serum gentamicin concentration after 21 days of treatment was detectable in only 2 dogs and was an order of magnitude below documented toxic concentrations.

Brain stem auditory evoked potentials from bone stimulation in dogs.

Brain stem auditory evoked potential (BAEP) testing with air-conducted click stimuli can be used to diagnose sensorineural deafness in dogs if conductive deafness can be ruled out. Detection of conductive deafness can be performed by recording BAEP elicited by a vibratory stimulus transducer placed against the skull. Air- and bone-conducted BAEP were compared in dogs, varying bone stimulator placement, click polarity, and stimulus intensity. Optimal bone stimulator placement was determined to be over the mastoid process, followed by the mandible and the zygomatic arch. Condensation polarity clicks gave responses preferable to those elicited by rarefaction or alternating polarity. Bone-conducted BAEP peak latencies were significantly longer than air-conducted latencies after correction of the latencies for the air conduction time accompanying air-conducted stimuli. Significant differences between stimulus modalities were not seen for BAEP peak amplitudes or interpeak latencies. Latency-intensity and amplitude-intensity regressions had similar effects for both modalities: latencies decreased and amplitudes increased as stimulus intensity increased.

Flash and pattern reversal visual evoked potentials in C57BL/6J and B6CBAF1/J mice.

Visual system responses (visual evoked potentials) to flash (FVEP) and pattern reversal (PRVEP) stimuli were recorded in mice. Two strains were used: black C57BL/6J mice and agouti B6CBAF1/J mice (first generation offspring of C57BL/6J females and CBA/J males.) Subjects were sedated with ketamine and xylazine. Flash rate (FVEP) and stimulus spatial frequency and pattern reversal rate (PRVEP) were varied to determine optimum stimulus parameters. Normative FVEP and PRVEP data were collected from mice of both strains after determination of optimum parameters. Five positive and four negative alternating peaks were routinely observed in the FVEP, while three positive and three negative alternating peaks were seen with the PRVEP. Varying the flash rate, the pattern reversal rate, and spatial frequency significantly affected nearly all amplitude and latency measures in the responses. Significant differences between strains were seen on some, but not all, latency and amplitude measures when the stimulus parameters were varied.

Daily rhythm of plasma insulin in Japanese quail (Coturnix c. japonica) fed ad libitum.

1. Plasma levels of immuno-reactive insulin (IRI) of 6 groups of 5-week-old quail, held on a 16L:8D photoregime, were measured every 4 hr, for 24 hr. 2. Concentrations of plasma IRI varied during the 24 hr period (Anova, P < 0.003). Insulin levels were high (mean = 857 pg/ml) from 6 a.m. (light onset) until 6 p.m. (4 hr before light offset) and low (mean = 185 pg/ml) at 10 p.m. and 2 a.m. 3. IRI concentrations at 6 a.m., 10 a.m., 2 p.m. and 6 p.m. were significantly different from values at 2 a.m. and 10 p.m. by Waller grouping. 4. Low IRI levels at light offset (10 p.m.--when the birds had full crops and were in an absorptive state) and high levels at light onset (6 a.m.--before feeding resumed) indicate that feeding does not fully account for the IRI rhythm.

Cortical somatosensory evoked potentials in cows.

A method was developed to record cortical somatosensory evoked potentials (SEP) from thoracic and pelvic limb stimulation in cows. Recordings were similar in latency and amplitude to those reported for horses. Correction for conduction pathway length did not alter the average latency values because the cows of the study were uniform in size; however, the data provided will enable use of this normative data with smaller or larger individual animals. Although latency variability for the SEP peaks was low, variability of the amplitude measurements was high. This observed variability was similar to that seen in other species. Validity of the recorded responses was indicated by lack of a tibial nerve SEP in 1 cow that had been given a tibial nerve conduction block, using lidocaine, and by repeatability of the response in 2 recordings taken 1 year apart in the same cow.

Brainstem auditory-evoked potential assessment of congenital deafness in Dalmatians: associations with phenotypic markers.

To screen for congenital deafness, brainstem auditory-evoked potential (BAEP) testing was performed on 1031 Dalmatians from three geographically separated areas. Phenotypic marker assessment was done to determine markers possibly associated with deafness. Markers included sex, hair coat color, pigmentation of different areas of skin (eye rims, nose, and ears), presence of a patch, spot size and marking (density of spotting), sire and dam BAEP status, and presence of iris and retinal tapetal pigmentation. Combined data from all test sites showed 8.1% bilateral deafness (N = 83 dogs) and 21.6% unilateral deafness (N = 223), or an overall 29.7% incidence of hearing disorders. Significant (P less than 0.05) associations with deafness for the data from all test sites combined were seen for patch, sire and dam BAEP, iris pigment, and retinal pigment. However, results differed for several of the significant phenotypic markers when analyses were done on the data from the individual test sites; changes from significant to not significant were found. This suggested the existence of multiple populations of deafness patterns, and reinforced the precautionary conclusion that associations of phenotypic markers with deafness are not necessarily functionally significant.

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.

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.

Hyperbaric oxygen effects on brown recluse spider (Loxosceles reclusa) envenomation in rabbits.

Human loxoscelism was modeled in albino rabbits by injection of brown recluse spider (Loxosceles reclusa) venom, and the effects of daily or twice-daily hyperbaric oxygen treatment on wound healing were investigated. Lesions similar to those seen in humans were produced in rabbits by intradermal injection of 200 microliters of a venom extract (0.21 microgram protein per microliter), including edema and erythema, ischemia and cyanosis in the first 12 hr, extensive purpura by 24 hr, and crateriform ulcer formation by day four, with induration and eschar formation. Hyperbaric oxygen treatments, consisting of two atmospheres absolute (2 ATA) for 60 min, were applied daily (n = 8) or twice daily (n = 8), while control animals (n = 8) received no treatment. Treatments were initiated 72 hr after venom injection (day 3) to duplicate typical clinical treatment delays, and were administered for seven consecutive days. No significant effects of hyperbaric oxygen treatment on lesion healing were seen as measured by lesion area. However, histologic evaluation of wound tissue collected at euthanasia on day 24 showed clear differences between rabbits receiving twice-daily treatments and those receiving daily or no treatment. The former showed complete re-epithelization or slight ulceration, while the latter usually had necrotic cavities extending into the dermis, with myonecrosis and inflammatory cell accumulation. Thus, no superficial differences were seen between groups, but twice-daily treatments resulted in enhanced recovery at the histologic level.

Visual evoked potentials in the clinically normal dog.

Visual evoked potentials (VEP) in response to flashes of white light were recorded from 15 adult beagles of both sexes to provide a normative data base. Separate recordings were taken by stimulating each eye of every dog. Responses were recorded from a needle electrode placed over the nuchal crest referenced to an electrode just caudal to the eyes. Five positive and negative peaks were present in each VEP; P1, N1, P2, N2, and P3. Peak P2 was the most prominent. Mean (+/- standard deviation [SD]) latencies for peaks P1, N1, P2, N2, and P3 were 14.3 +/- 2.4, 29.2 +/- 2.2, 54.5 +/- 7.4, 78.0 +/- 13.1, and 98.1 +/- 12.6 msec, respectively. Peak-to-peak mean amplitudes ranged from 5.88 to 13.30 microV. Recordings were accomplished without sedation, anesthesia, or mydriatic drugs.