Quantitative assessment of pupillary light reflex in normal and anesthetized dogs: a preliminary study

The purpose of this study was to quantitatively assess the pupillary light reflex (PLR) in normal and anesthetized dogs using a pupillometer. Eleven dogs (20 eyes) of various breeds were included. PLRs were measured with a handheld pupillometer in dim light before and during anesthesia. Anesthesia was conducted with atropine, xylazine and ketamine. Parameters of pupillometry included neurological pupil index (NPi), pupil size, percent of change (%CH), latency (LAT), constriction velocity (CV), maximum constriction velocity (MCV) and dilation velocity (DV). NPi,%CH, CV and MCV were significantly decreased during anesthesia compared with the pre-anesthesia data. The results suggest that atropine-xylazine-ketamine combination anesthesia depresses the PLR. Additionally, this study demonstrates the feasibility of the use of a pupillometer in dogs.     

The development of the pupillary light reflex and menace response in neonatal lambs and kids

The aim of this study was to investigate the development of the pupillary light reflex and menace response in neonatal lambs and goat kids. Thirty lambs and 33 kids were assessed daily from birth until the pupillary light reflex and menace response had become established. All animals had a controlled pupillary light reflex within 20 h of birth. Lambs and kids had developed menace responses by 8 ± 3 and 14 ± 2 days, respectively. The Mann–Whitney test revealed a significant difference (P < 0.001) in the ages at which lambs and kids developed a menace response. Male kids developed this response significantly (P = 0.006) later than females. There was no sex difference in the menace response in the lambs. Overall, the findings indicated that lambs develop a menace response earlier than kids, and female kids develop this response more rapidly than their male counterparts.     

The pupillary light reflex and menace response in neonatal calves: the role of environmental isolation on development of the menace response

The aim of this study was to investigate the development of the pupillary light reflex in neonatal calves and the effect on the development of the menace response of keeping them in individual stalls. Seventy-three Holstein calves were divided into test (n = 44) and control (n = 29) groups and the animals were kept in individual stalls for the first 32 ± 4 and 73 ± 5 days post partum, respectively. They were then moved to group pens. All calves in both groups were observed daily from the first day after birth until the pupillary light reflex and menace response had become well established.All 73 calves had a positive pupillary light reflex on the first day post partum. None of the animals developed a menace response during the time they were housed in individual stalls. Over 14 days (test group) and 12 days (control group) after the calves had been moved to the group pens they became positive to the menace response at ages 41 ± 4 and 81 ± 5 days, respectively. The Mann–Whitney test revealed a significant difference (P < 0.001) in the ages of the calves with positive menace responses between groups. Group rearing may produce more visual threats to the eyes and the calves learn the menace response by closing the lids in response to sudden alarming movements.     

Effects of hereditary retinal degeneration due to a CEP290 mutation on the feline pupillary light reflex

Objective To understand how progressive rod cone degeneration due to a mutation in CEP290 affects the pupillary light reflex (PLR) in domestic cats. Animals studied Domestic cats identified as either normal wildtype (WT; n = 6), or homozygous for the rdAc mutation in CEP290 and having early stage retinal degeneration (stage 2, S2; n = 4), or advanced retinal degeneration (S4; n = 6). Methods The effect of light on pupil size was measured over a series of 10‐s pulses of white and chromatic light in cats lightly sedated with medetomidine. Results In WT cats, the PLR was characterized by a pronounced initial constriction that rapidly re‐dilated during the stimulus (pupil escape), to a stable or sustained constriction. There was then a marked constriction at stimulus offset. Each component of the PLR was retained in affected cats, but with progressively reduced irradiance sensitivity from early to advanced retinal disease. Conclusions The PLR of cats had multiple phases, with a remarkably high‐amplitude ‘paradoxical’ off‐constriction even in the absence of retinal disease. In rdAc cats, reduced irradiance sensitivity was consistent with progressive loss of rod and cone function. Based on previously characterized retinal pathology, this suggests the visual streak of the retina has a proportionally large contribution to PLR input. These findings support the hypothesis that the efficacy of planned therapeutic trials can be determined by careful evaluation of the PLR in cats.     

Quantitative assessment of nociceptive processes in conscious dogs by use of the nociceptive withdrawal reflex

OBJECTIVE: To investigate the feasibility of evoking the nociceptive withdrawal reflex (NWR) from fore and hind limbs in conscious dogs, score stimulus-associated behavioral responses, and assess the canine NWR response to suprathreshold stimulations. ANIMALS: 8 adult Beagles. PROCEDURE: Surface electromyograms evoked by transcutaneous electrical stimulation of ulnaris and digital plantar nerves were recorded from the deltoideus, cleidobrachialis, biceps femoris, and tibialis cranialis muscles. Train-of-five pulses (stimulus(train)) were used; reflex threshold (I(t train)) was determined, and recruitment curves were obtained at 1.2, 1.5, and 2 x I(t train). Additionally, a single pulse (stimulus(single)) was given at 1, 1.2, 1.5, 2, and 3 x I(t train). Latency and amplitude of NWRs were analyzed. Severity of behavioral reactions was subjectively scored. RESULTS: Fore- and hind limb I(t train) values (median; 25% to 75% interquartile range) were 2.5 mA (2.0 to 3.6 mA) and 2.1 mA (1.7 to 2.9 mA), respectively. At I(t train), NWR latencies in the deltoideus, cleidobrachialis, biceps femoris, and cranial tibialis muscles were not significantly different (19.6 milliseconds [17.1 to 20.5 milliseconds], 19.5 milliseconds [18.1 to 20.7 milliseconds], 20.5 milliseconds [14.7 to 26.4 milliseconds], and 24.4 milliseconds [17.1 to 40.5 milliseconds], respectively). Latencies obtained with stimulus(train) and stimulus(single) were similar. With increasing stimulation intensities, NWR amplitude increased and correlated positively with behavioral scores. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, the NWR can be evoked from limbs and correlates with behavioral reactions. Results suggest that NWR evaluation may enable quantification of nociceptive system excitability and efficacy of analgesics in individual dogs.     

Analgesia and chemical restraint for the emergent patient.

This article discusses analgesia and chemical restraint for the emergency patient. As illness or injury affect all organ systems, specific recommendations and considerations of analgesic, anesthetic, and restraining regimens are presented. As animals of all ages, from neonates to geriatric and those that are pregnant or lactating,may require management of their illness or injury, recommendations for these patients are also presented.     

Pre-operative stress in dogs - a preliminary investigation of behavior and heart rate variability in healthy hospitalized dogs

OBJECTIVE: To assess pre-operative behavioral and physiological characteristics of healthy dogs hospitalized for elective surgery. STUDY DESIGN: Open clinical observational study. ANIMALS: Forty-one bitches hospitalized for elective ovariohysterectomy. METHODS: While undisturbed in a hospital cage, the behavior of the dog was recorded using a video camera and recorder. From the video recordings, various behavioral variables were registered. Simultaneous measurements were made on heart rates and heart rate variability (HRV) by use of an ambulatory electrocardiogram. In addition, the dog's response to human approach was noted. RESULTS: Different behavioral patterns were found in the dogs studied. Thirteen individuals were regarded as highly active, and were seen to bark or howl, manipulate the environment or attempt to flee vigorously. In 13 dogs (passive dogs) none of these activities occurred. Panting and displacement behaviors, such as snout licking, were observed in nearly all the animals monitored. In general, heart rates were higher and HRV lower with the most active individuals; however, the presence of physiological arousal could not be excluded in two animals with passive behaviors. To some extent, the behavior of the dog while undisturbed in the cage was reflected in the responses to a person entering the cage. CONCLUSIONS AND CLINICAL RELEVANCE: The different individual responses detected in this study raise an important question concerning their role and existence throughout the entire peri-operative period, especially during the post-anesthetic recovery phase when behavioral characteristics are commonly used to assess patient welfare. The results also emphasize the need for further investigations to explore the effects of pre-operative stressors on canine surgical patients, and the factors contributing to them.     

Noninvasive assessment of the facilitation of the nociceptive withdrawal reflex by repeated electrical stimulations in conscious dogs

OBJECTIVE: To investigate the facilitation of the nociceptive withdrawal reflex (NWR) by repeated electrical stimuli and the associated behavioral response scores in conscious, nonmedicated dogs as a measure of temporal summation and analyze the influence of stimulus intensity and frequency on temporal summation responses. ANIMALS: 8 adult Beagles. PROCEDURES: Surface electromyographic responses evoked by transcutaneous constant-current electrical stimulation of ulnaris and digital plantar nerves were recorded from the deltoideus, cleidobrachialis, biceps femoris, and cranial tibial muscles. A repeated stimulus was given at 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and 1.1 x I(t) (the individual NWR threshold intensity) at 2, 5, and 20 Hz. Threshold intensity and relative amplitude and latency of the reflex were analyzed for each stimulus configuration. Behavioral reactions were subjectively scored. RESULTS: Repeated sub-I(t) stimuli summated and facilitated the NWR. To elicit temporal summation, significantly lower intensities were needed for the hind limb, compared with the forelimb. Stimulus frequency did not influence temporal summation, whereas increasing intensity resulted in significantly stronger electromyographic responses and nociception (determined via behavioral response scoring) among the dogs. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, it is possible to elicit nociceptive temporal summation that correlates with behavioral reactions. These data suggest that this experimental technique can be used to evaluate nociceptive system excitability and efficacy of analgesics in canids.     

Artificial light at night decreases the pupillary light response of dark-adapted toads to bright light

Artificial light at night (ALAN) is expanding worldwide. Many physiological effects have been reported in animals, but we still know little about the consequences for the visual system. The pupil contributes to control incoming light onto the retina. Sudden increases in light intensity evokes the pupil light reflex (PLR). Intrinsically photosensitive retinal ganglion cells (ipRGC) affect PLR and melatonin expression, which largely regulate circadian rhythms and PLR itself. IpRCG receive inputs from various photoreptors with different peak sensitivities implying that PLR could be altered by a broad range of light sources. We predicted ALAN to enhance PLR. Contrary to our prediction, dark-adapted cane toads Rhinella marina, exposed to ALAN (5 lx) for 12 days, exhibited a lower PLR than controls and individuals exposed to 0.04 lx, even after 1 h in bright light. We cannot conclude whether ALAN induced a larger pupil size in dark-adapted toads or a slower initial contraction. Nevertheless, the response was triggered by a light source with an emission peak (590 nm) well above the sensitivity peak of melanopsin, the main photoreceptor involved in PLR. Therefore, ALAN alters the capacity of toads to regulate the incoming light in the eye at night, which may reduce the performance of visually guided behaviors, and increase mortality by predators or road kills at night. This first study emphasizes the need to focus on the effect of ALAN on the vision of nocturnal organisms to better understand how this sensory system is altered and anticipate the consequences for organisms.     

Sedation and chemical restraint in the dog and cat

Small animal patients must often undergo veterinary procedures that are painful or distressful, for which judicious use of sedatives or other agents with anesthetic or analgesic properties can be useful. If the degree of sedation is profound enough, such "chemical restraint" may be employed to provide immobilization for radiographs or minor surgical procedures. The choice of agents to be used will depend upon the physiologic state and cooperative nature of the patient and the desired endpoint, ie, anxiolysis versus deep sedation with analgesia. This report discusses important features of patient assessment, preparation, equipment needs, consideration of the types of procedures for which sedation is useful, and recovery considerations. A brief review is included of the useful effects and contraindications for the various agents employed, and doses for each are listed. Algorithms are presented for a given category of patient, leading the practitioner through a decision making strategy to arrive at examples of sedation or chemical restraint protocols that are commonly found to be effective by the author.     

Cephalexin in ponies: a preliminary investigation

The administration of a single dose of the antibacterial agent cephalexin intramuscularly to six ponies at a dose rate of 7 mg/kg was well tolerated. No reactions at the injection site were apparent. It was absorbed rapidly and reached a mean peak plasma concentration of 6.77 micrograms/ml after a mean of 1.41 hours; plasma concentrations above 2.0 and 0.5 micrograms/ml were maintained for 3.8 and 9.8 hours, respectively.     

Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses

Objective To assess the effectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. Design Retrospective study. Animals Fifty‐one adult horses aged 9.5 ± 6.9 years (range 1–23 years) and weighing 575 ± 290.3 kg. Methods Records of horses presented to our clinic over a 3‐year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. Results Detomidine was administered as an initial bolus loading dose (mean ± SD) of 7.5 ± 1.87 µg kg^?1. The initial infusion rate was 0.6 µg kg^?1 minute^?1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses. Conclusions Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. Clinical relevance An effective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide sufficient analgesia for surgery and a significant proportion of animals required supplemental sedatives and analgesics.     

A technique for resection of invasive tumors involving the trigone area of the bladder in dogs: preliminary results in two dogs

Objective— To describe a surgical technique for resection of the entire bladder neck, including the trigone and proximal urethra in dogs with invasive tumors causing life-threatening urinary tract obstruction.
Study Design— Clinical case reports.
Animals— Dogs (n=2) with bladder tumors.
Methods— Circumferential excision of the bladder neck and proximal urethra with preservation of the neurovascular pedicles was performed to remove a rhabdomyosarcoma (dog 1) and a transitional cell carcinoma (dog 2) involving the trigone and bladder neck that were causing urinary tract obstruction. Reconstruction of the bladder and proximal urethra included bilateral ureteroneocystostomy. Adjuvant chemotherapy was administered postoperatively to both dogs.
Results— Postoperatively, dogs 1 and 2 were continent after 7 and 17 days, respectively, and regained normal urinary function after resolution of a transient pollakiuria. Dog 1 had no evidence of local or regional recurrence; however, a large solitary pulmonary metastatic lesion was diagnosed 8 months later. The dog was euthanatized despite a lack of clinical signs. Dog 2 had at least 1 metastatic lesion in the abdominal wall 6 months later and was euthanatized at 580 days because of renal failure.
Conclusion— En-bloc removal of the bladder neck and proximal urethra with preservation of the dorsal vascular and nervous pedicles, although a technically challenging procedure, can be performed without associated urinary incontinence or bladder wall necrosis.
Clinical Relevance— In dogs with invasive bladder tumors causing life-threatening urinary tract obstruction, resection of the bladder neck and proximal urethra should be considered as a promising surgical alternative to urinary diversion.     

Distribution of propionibacteria on dogs: A preliminary report of the findings on 11 dogs

A microdissection technique was used to investigate the flora of the canine skin surface and hair follicle. Anaerobic incubation revealed a species of Propionibacterium on the skin of seven of 11 normal dogs. The organism had cultural and biochemical similarities to Propionibacterium acnes. Analysis of the distribution of the organism revealed significant differences between carriage on males and females, between dogs with long and shorthaired coats and between dogs with coarse and fine hair. When present, the regional distribution of P acnes was similar to that found on man, with higher numbers found on the trunk than on the feet.     

A combination chemical/physical method for repeated restraint of turkeys

A method for the repeated long-term restraint of young turkey toms was developed. Fifteen mg xylazine/kg body weight was administered intramuscularly (IM) to each of 60 toms whose heads and bodies were then covered with surgical stockinette secured with adhesive tape during a total of 229 restraint events (RE). Toms then were restrained in dorsal recumbency for 2, 4, or 6 hr daily for 4 days. Those restrained for 6 hr received an additional IM injection of 10 mg xylazine/kg body weight after 3 hr of restraints. Three toms with airsacculitis or pneumonia died during restraint, and one with pneumonia died during the night between RE. The mean body temperature of restrained toms declined during the first 150 min of RE and then stabilized. Toms restrained 6 hr daily lost weight during the 4 treatment days. Toms restrained 2 hr and 4 hr gained weight, but the latter group did not gain weight as quickly as the former.