Recording of visual-evoked potentials in dogs with scalp electrodes.

Following unsuccessful attempts to record visual-evoked potentials (VEPs) in dogs with scalp electrodes, adoption of a new stimulation technique seems to be beneficial. Previously, flashes of white light administered after dark adaptation induced relatively high amplitude electroretinograms (ERGs) covering any VEP activity over the surface of the skull. ERG amplitude, however, can be significantly reduced using flashes of red light after light adaptation (mostly cone stimulation). Simultaneous ERG and VEP recording allows identification of VEPs composed of three significantly different negative peaks (N1, N2, and N3) measured in dogs anesthetized with chloralose and halothane. No more than two of the three peaks were seen in one recording. Only the N1 and N3 waves were consistently recorded in dogs anesthetized with thiopental and thiopental combined with halothane. In 50% of all recordings, N1 was seen alone. The other VEPs consisted of N1 and N2, or N1 and N3 occurring concurrently. The simultaneous occurrence of N2 and N3 waves, however, was never seen. Among all recordings, N1 was most frequently recorded (85% of measurements), followed by N3 and N2 (38% and 31% of measurements, respectively). Peaks of less than 90 ms are highly reproducible. Anesthesia is necessary to eliminate frequent artifacts obtained in conscious and sedated dogs. Thiopental and/or halothane had no effect on measured latencies compared with chloralose.

Blood pressures obtained by indirect measurement in conscious dogs.

Heart rate and arterial systolic, mean, and diastolic blood pressures were measured indirectly in apparently healthy dogs in clinical situations (examination rooms, cages, or runs) and in 3 groups of abnormal dogs. An electronic automatic sphygmomanometer measured and analyzed arterial pulses (oscillometric method). Apparently healthy dogs had a mean +/- SD heart rate of 134 +/- 32 beats/min and systolic, mean, and diastolic pressures of 144 +/- 27, 110 +/- 21, and 91 +/- 20 mm of Hg, respectively. The mean systolic pressure was significantly higher in hospitalized dogs than in nonhospitalized dogs. When compared with relaxed dogs, playful dogs had a higher mean heart rate. Apprehensive dogs had a higher mean diastolic pressure than did relaxed dogs. The mean heart rate and blood pressures of panting dogs were not significantly different from the mean values from relaxed dogs. Heavier (greater than 18 kg) and older (greater than 2 years) dogs had lower mean heart rates and higher pressures, compared with lighter (less than or equal to 18 kg) and younger (less than or equal to 2 years) dogs. Infection with Dirofilaria immitis had no effect on heart rate and blood pressures when compared with apparently healthy dogs. Dogs with renal failure had a significantly higher mean diastolic pressure and dogs with mitral regurgitation had a significantly lower mean diastolic pressure, compared with apparently healthy dogs.

Disseminated protothecosis causing acute blindness and deafness in a dog.

A 3-year-old Collie bitch was euthanatized two weeks after the onset of blindness and deafness. The hearing deficit had been localized by clinical signs, brain stem auditory evoked responses, and impedance audiometry. Protothecosis was diagnosed by cytologic and histologic examinations. The organism was identified as Prototheca zopfii . Organisms and granulomatous lesions were found in kidney, heart, liver, skeletal muscle, thyroid gland, colon, bronchial lymph node, brain, and cochlea.

The effects of halothane-and-oxygen anesthesia, and of halothane-nitrous oxide-and-oxygen anesthesia on tympanograms in the dog.

Electroacoustic tympanograms were recorded from both ears of 20 dogs of either sex, aged 6 mo to 12 yrs, prior to anesthesia, at 10 min after halothane- and-oxygen (HO) anesthesia, and at 5 min after nitrous oxide was added to the HO mixture (HNO). Both HO and HNO anesthesia significantly increased compliance and peak pressure values from pre-anesthetic (own control) values. In addition, HNO anesthesia significantly increased peak pressure values above HO anesthesia levels. HNO compliance values were not significantly different from HO values. These results suggest that tympanograms recorded during either HO or HNO anesthesia in the dog will be altered and that interpretation of the tympanograms should include consideration of the state of consciousness of the animal during recording.

Simple, accurate method for clinical estimation of glomerular filtration rate in the dog.

Simultaneous [14C]inulin and exogenous creatinine clearance procedures were performed on 10 healthy adult dogs of both sexes after constant IV infusions of inulin and a single subcutaneous injection of creatinine. For 30 clearance procedures determined for 10 dogs, the creatinine/inulin (C/I) clearance ratio was 1.03 +/- 0.01, and the results of the 2 tests were highly correlated (r = 0.91). Simultaneous [14C]inulin and endogenous creatinine clearance procedures were performed in the same 10 dogs. For 30 clearance procedures in these dogs, the C/I clearance ratio was 0.70 +/- 0.06 and the 2 tests were less highly correlated (r = 0.79). Fifteen clearance procedures of the same design were conducted on 5 dogs with azotemia induced by surgical reduction of renal mass. In these dogs, the exogenous C/I clearance ratio was 1.09 +/- 0.12, and the endogenous C/I clearance ratio was 0.89 +/- 0.07. It was concluded that the single injection method of exogenous creatinine clearance was a valid method for clinical measurement of glomerular filtration rate in the female dog and would closely approximate glomerular filtration rate in male dogs without azotemia. At normal or near normal plasma creatinine levels, the endogenous creatinine clearance procedure gave erroneously low values for glomerular filtration rate when the common methods of creatinine analysis were used.

Kinetics of gentamicin after intravenous, intramuscular, and intratracheal administration in sheep.

Kinetics of gentamicin (2.2 mg/kg of body weight) were investigated in 7 sheep after IV bolus administration. The mean serum concentration profile could be described by a 2-compartment open model with a distribution rate constant (alpha) of 3.112 +/- 1.681 hour-1 [half-life, t1/2(alpha) = 17.22 +/- 8.63 minutes] and an overall elimination rate constant (beta) of 0.485 +/- 0.028 hour-1 [t1/2(beta) - 85.87 +/- 5.03 minutes]. The apparent volume of distribution was somewhat restricted [Vd(area) = 0.194 +/- 0.059 L/Kg], and the total body clearance was 1.559 +/- 0.400 ml/kg/min. Equal dosages of gentamicin (2.2 mg/kg) were also given IM and intratracheally (IT). after IM injection, gentamicin reached peak serum concentration at postinjection minutes (PIM) 45, surpassing concentrations after the IV injection for the remainder of the experiment. The IT injection produced detectable serum concentrations at PIM 5, with a peak concentration at PIM 60. The serum drug concentrations after IT injections remained well below concentrations after IV and IM injections. Radiographic analysis of an IT injection of a gentamicin-tantalum suspension revealed good distribution throughout the trachea and proximal bronchi, with physical clearance of the tantalum occurring after greater than or equal to 10 minutes. Aspiration biopsy of the tracheal wash 6 hours after IT gentamicin injection revealed no cytologic response to gentamicin in 6 of 7 sheep, with the single response that of a purulent exudate.

Orientation and configuration of vectorcardiographic QRS loops from normal cats.

The orientations (angles) of mean QRS vectors were manually calculated from scaler orthogonal leads (I, aVf, V10; X, Y, Z) and from X-Y oscilloscope recordings from cats injected with ketamine and acetylpromazine. Those angles calculated from individually recorded leads (I, aVf, and V10) were from cats in right lateral and sternal recumbency. Leads, X, Y, and Z were recorded simultaneously from cats in the sternal recumbency. The oscilloscope recordings were derived from the X, Y, and Z leads. Arithmetic and maximal measurements from ECG scaler leads and maximal and half-area measurements from oscilloscopic recordings were used for calculations. Recordings from 15 cats and from 1 cat 15 times. Based on visual inspection of scattergrams, the X, Y, and Z vectors were not different in orientation from I, aVf, and V10 vectors. Orientation of oscilloscopic vectors were more variable than orientations of vectors calculated from scaler leads. Body position of the cat during recording did not affect mean values of angles derived from leads I, aVf, and V10. Type of measurements did not affect mean values. Variation of orientation was greater among cats than for the intraindividual vector orientations. Configuration and direction of QRS loops from 27 normal cats were also recorded. The greatest variation in loop configuration was in the frontal plane.

Electroretinographic components of the canine visual evoked response.

Electroretinograms (ERG) and visual evoked responses (VER) were recorded from 2 anesthetized dogs before and after surgical manipulation. The ERG was recorded from a corneal contact lens, and the VET, from 9 different scalp sites. The recordings were made on a signal averager as done in clinical situations. Surgical manipulation consisted of an alcohol block of the stimulated eye and enucleation of the nonstimulated eye. The results indicated that under the conditions of making the recordings, the major and consistent waves of the VER from all scalp sites were a far-field ERG and were not of cortical origin.

Determination of blood pressure by indirect methods in dogs given acetylpromazine maleate.

This study was designed to monitor and compare indirect blood pressures by two methods (ultrasonic Doppler and photoelectric) after intravenous acetylpromazine maleate at three different doses (0.11, 0.55, and 1.10 mg/kg). Sixteen unanesthetized dogs were placed in right lateral recumbency and pressures estimated from the left hind leg at two preinjection times and at 3, 15, 60 and 120 minutes postinjection. This procedure was followed for each dog for each of the three doses. Preinjection ultrasonic mean values and standard deviations were similar to published values. Photoelectric systolic pressures were lower and diastolic pressures higher than ultrasonic systolic and diastolic pressures. The decrease in blood pressure was detected by both methods. Neither method revealed a dose related response.

Effects of neomycin on the waveform of auditory-evoked brain stem potentials in dogs.

Neomycin sulfate was administered intravenously to eight mixed-breed dogs at a dosage of 30 mg/kg/day for as long as 50 days. Auditory-evoked brain stem potentials (AEBP) were recorded from the dogs three times a week. The AEBP amplitudes and latencies from the eight treated and the eight control dogs were compared. All treated dogs eventually exhibited an isoelectric AEBP. The time required for the AEBP waveform loss to occur in the treated dogs varied between 22 and 50 days. The AEBP waveforms were still isoelectric when measured as long as 150 days after neomycin administration was stopped. The fact that AEBP did not return would tend to support the findings of others that the loss of the receptors in the inner ear, due to neomycin toxicity, is permanent. The results of this electrophysiologic study indicate that the organ of Corti (organum spirale) is the site of pathologic changes in the auditory system that result from neomycin treatment.

Glycogen and other soluble glucans from chytridiomycete and oomycete species.

Dry weight, protein, lipid, and glycogen were determined at various times during cultivation of the Chytridiomycetes, Rhizophydium sphaerotheca and Monoblepharella elongata. M. elongata had relatively stable levels of glycogen, but, in R. sphaerotheca, glycogen levels showed significant changes, particularly in older cultures in which a depletion of glycogen was accompanied by a marked thickening of the cell walls. Glycogen was a significant cellular constituent in both chytridiomycete species. In R. sphaerotheca and M. elongata, respectively, glycogen accounted for as much as 6% and 8.1% of the dry weight. In purified glycogens of both species, only alpha-1,4- and alpha-1,6-linked glucosyl residues were detected and the absorbance spectra of I2-complexes were similar to those of other well characterized glycogens. Purified Rhizophydium glycogen had a beta-amylolysis limit of 43%, and a CL of approximately 12. For the Monoblepharella polysaccharide, the respective values were 45% and 11. In extracts of the Oomycetes, Pythium debaryanum, Mindeniella spinospora, and Apodachlya sp., only beta-1,3- and beta-1,6-linked glucosyl residues were detected. These glucans were not iodophilic nor were they sensitive to alpha-amylase and beta-amylase. The properties of the oomycete polysaccharides suggested that they were similar to the mycolaminarans of Phytophthora spp. Although both investigated chytridiomycete species produced glycogen with typical properties, glycogen was apparently absent in the investigated Oomycetes.

Electroretinograms from broilers fed aflatoxin and T-2 toxin.

Thirty chicks were fed a commercial broiler grower ration from hatching to 26 days of age. Ten birds received aflatoxin (5 microgram/g. of ration) and 10 received T-2 toxin (5 microgram/g. of ration). The remaining 10 birds served as controls. After the 26 days, electroretinograms were recorded on a graphic recorder from the anesthetized birds. On the basis of wave amplitudes and durations from electroretinograms recorded in light and darkness and from different colored stimuli, no differences were detectable between treated birds and controls. Thus, the photochemistries of the retina were not sufficiently altered in this study to permit early detection of mycotoxicoses by electroretinograms.

Effects of asphyxia and potassium on canine and feline electrocardiograms.

The effects of asphyxia and potassium on the electrocardiogram (ECG), lead II, were recorded from dogs and cats anesthetized with sodium pentobarbital and halothane. Electrocardiographic recordings were made during control periods, during asphyxia (occluded endotracheal tube), during infusion of an isotonic KCl solution and during infusion of an isotonic NaCl solution. Arterial and venous blood gas partial pressures (PaCO2, PvCO2, PaO2 and and PvO2), plasma Na+ and K+ concentrations, heart rate and mean arterial blood pressure were measured during control periods, asphyxia and during the periods of infusion. The vagi were severed to assess the effect of vagal tone on the ECG changes. The characteristic ECG changes during asphyxia and the electrolyte imbalances resulting from infusion of isotonic KCl and NaCl were determined during sodium pentobarbital and halothane anesthesia in both dogs and cats. The combination of halothane and high PCO2 caused cardiac arrhythmias. Spontaneous recovery from ventricular fibrillation, as a result of hyperkalemia, was recorded from cats. Disappearance of the P waves, which is characteristic of hyperkalemia, was infrequent in this study and the U waves associated with hypokalemia were not found. Severing the vagi did not alter the ECG changes characteristic of asphyxia, hyperkalemia and hypokalemia. It was found that asphyxia and infusion of fluids high or low in potassium can produce ECG changes in both dogs and cats that can be correlated with blood gas partial pressure changes or plasma potassium concentrations.