Katherine A. Houpt

Gastrointestinal factors in hunger and satiety

The evidence for the participation of signals from the gastrointestinal tract in hunger and satiety is reviewed. Various methods of subjecting only certain portions of the gastrointestinal tract to food are described including sham feeding, crossing of the intestines of two animals, and intragastric, intraduodenal and intravenous feeding. These methods have revealed that animals eat more when only the mouth is exposed to food, but consume less when food enters the stomach directly and still less when feeding themselves intravenously. The role of the stomach in satiety is discussed in relation to the results of the many experiments in which intragastric loads were administered. These experiments generally revealed that gastric loads suppressed intake in proportion to their caloric value, but that compensation was not precise. A similar analysis is made of the role of the intestines in satiety. These studies present evidence for osmoreceptors and glucoreceptors, distention, and pressure, all of which may participate in satiety. The numerous effects of vagotomy on food intake are reviewed and an attempt is made to separate afferent from efferent effects and vagal effects from nonspecific surgical injury. The role of other afferents is explored. A brief survey of the most recent studies on humoral factors indicates that cholecystokinin is probably acting as a satiety agent, but its mode of action remains unknown. The changes in the gastrointestinal tract that accompany an increase or decrease in food intake reveal adaptive changes that occur in the organ. The evidence for gastrointestinal factors in satiety of the suckling animal is presented. Finally, a hypothesis is presented in which the various factors that bring a meal to an end are included. Preabsorptive satiety may consist of multiple factors which probably include signals from osmoreceptors and possibly other chemoreceptors in the upper small intestine. The signals from these receptors are neural while other products of digestion stimulate the release of humoral agents, such as cholecystokinin, which may act locally, in the liver, or on the central nervous system. Stretch or distention of the intestines at various locations may also contribute to preabsorptive satiety.

Dominance hierarchies in domestic horses

Abstract Dominance hierarchies were studied in 11 herds of domestic horses and ponies ( Equus caballus ). A paired feeding test was utilized to establish the dominance—subordination relationship between each pair of animals in a herd. Aggressive actions, threats, bites, kicks and chases were also recorded. In small herds linear hierarchies were formed, but in large herds triangular relationships were observed. Aggression was correlated with dominance rank. Body weight, but not age, appear to affect rank in the equine hierarchy. Juvenile horses were more likely to share feed with each other than were adult horses and were usually subordinate to adult horses. The daughters of a dominant mare were dominant within their own herds.

Comparison of cerebrospinal fluid monoamine metabolite levels in dominant-aggressive and non-aggressive dogs

Aggression has been shown to be related to reduced serotonergic activity in humans and non-human primates, and in rodents. We now studied the relationship between cerebrospinal fluid (CSF) monoamine metabolites and canine aggression in 21 dominant-aggressive dogs (Canis familiaris) and 19 controls. The diagnosis of dominance-related aggression was based upon a history of biting family members in contexts associated with dominance challenges. Post-mortem CSF 5-HIAA, MHPG and HVA were measured by high-performance liquid chromatography using electrochemical detection. Concentrations of CSF 5-HIAA (P = 0.01) and HVA (P < 0.001) were lower in the aggressive group (median values: 5-HIAA 202.0 pmol/ml; HVA 318.0 pmol/ml) than in controls (5-HIAA 298.0 pmol/ml; HVA 552.0 pmol/ml). No differences were noted in CSF MHPG levels. Differences in 5-HIAA were maintained after controlling for breed and age of dogs, but HVA differences may have been breed-dependent. Lower levels of 5-HIAA (P = 0.02) and HVA (P = 0.04) were found in the subgroup of aggressive dogs with a history of biting without warning (5-HIAA 196.0 pmol/ml; HVA 302.0 pmol/ml) compared to dogs that warned (5-HIAA 244.0 pmol/ml; HVA 400.0 pmol/ml). This study suggests that reduced serotonergic function is associated with aggressive behavior and impaired impulse control in dogs, a finding that is consistent with observations in primates, and suggests that serotonin modulates aggressive behavior throughout mammals.

The 24-Hour Time Budget of Przewalski Horses

Abstract A herd of 8 Przewalski horses were observed on pasture in summer. Fifteen-minute focal animal samples were used to determine the time budget of the horses during the periods 00.00–04.00, 04.00–08.00, 08.00–12.00, 12.00–16.00, 16.00–20.00 and 20.00–24.00 h EDT. The behavioral states recorded were feeding (grazing and eating grain), nursing, drinking, standing, stand-resting, self-grooming, mutual grooming, locomoting, playing, and lying laterally and sternally. The average number of behavioral states occurring per hour, and the defecation, urination, aggression and vocalization rates were also determined. Overall, the horses spent 46.4 ± 5.9% of their time feeding, 1.3 ± 0.1% nursing, 0.5 ± 0.1% drinking, 20.6 ± 5.4% standing, 15.7 ± 3.2% stand-resting, 1.7 ± 0.2% self-grooming, 2.2 ± 0.7% mutual grooming, 7.4 ± 1.0% locomoting, 1.2 ± 0.3% playing, 1.2 ± 0.5% lying laterally and 4.1 ± 3.0% lying sternally. The horses averaged 45.2 ± 5.8 behavioral states per hour, and 0.2 ± 0.0 defecations, 0.3 ± 0.0 urinations, 1.5 ± 0.3 aggressions and 0.7 ± 0.1 vocalizations per hour. The horses spent the greatest amount of time foraging between 20.00 and 04.00 h, when the temperatures were lower. They spent 68.2 ± 2.2% of their time between 20.00 and 24.00 h feeding, but only 31.2 ± 2.1% of their time feeding between 08.00 and 12.00 h. Recumbent rest was most common between 00.00 and 04.00 h. As temperatures rose during the daylight hours, the horses spent more time drinking and standing, rather than grazing. Stand-resting was the most common form of rest during the day. The horses exhibited the greatest number of activities per hour from 08.00 to 20.00 h. While standing in close proximity to one another during these hours, the horses exhibited the highest number of aggressions per hour (1.9–2.4).

Satiety elicited by cholecystokinin in intact and vagotomized rats

Abstract The effect of exogenous cholecystokinin and gastric loads of substances shown to release endogenous cholecystokinin were investigated in rats. Intraperitoneal injection of cholecystokinin and caerulein produced a significant suppression of food but not water intake. Phenylalanine (the L but not the D isomer), egg yolk and 0.1 N HCl but not MgSO 4 depressed feeding in the fasted rats. This satiety effect does not seem to be mediated via the vagus nerve, as suppression of food-intake was observed after subdiaphragmatic vagotomy. Blocking of pancreatic enzyme secretion does not prevent cholecystokinin-induced satiety.

Differences in background and outcome of three behavior problems of dogs

In order to characterize the three major behavior problems, aggression toward owners, aggression toward strangers and separation anxiety, backgrounds of dogs and general outcomes of the behavioral treatments were analyzed retrospectively. There were 169 cases of aggression toward owners, 84 cases of aggression toward strangers and 78 cases of separation anxiety which did not overlap each other during the 5 years from 1993 to 1997 at Cornell University Animal Behavior Clinic. Based on the case records, including discharge instructions, follow-up information, and pre-presentation questionnaires, several variables were compared among these three groups. The sexual status of these groups was not statistically different, although dogs with aggression toward owners had the highest proportion of males and there were more males in all behavior groups than in the hospital population. Also, breed types were different among three groups with a significantly higher proportion of mixed breed dogs among dogs with separation anxiety and aggression to strangers as compared to dogs with aggression to owners and to the hospital population. A higher percentage of dogs in the separation anxiety group tended to live in apartments and to be disciplined only verbally by the owner than in the other two groups. Age differences were apparent among the three groups in relation to when the dogs were obtained, and the separation anxiety group was different from at least one of the other groups in the age when first obtained, the age the owners first noticed the problem, and the age of behavioral examination. Regarding the general outcome of the behavioral treatment, there were no significant differences among the behavioral groups with regards to the proportion of dogs reported improved. These results provide new characterizations of these three major behavior problems.

Urine spraying in cats: presence of concurrent disease and effects of a pheromone treatment

Abstract Thirty four spraying cats, belonging to 24 households, had a complete physical examination, CBC, blood biochemistry panel, urinalysis, urine culture, urine cortisol:creatinine analysis and abdominal radiographs. Diagnostic procedures revealed some abnormalities and/or crystalluria in 13 patients (38%). Seven (20%) of these cats had medical conditions involving the urogenital system (renal calculi, renal failure, cystic calculi, bacterial urinary infection or cystitis associated with the presence of ammonium biurate crystalluria). The other six had crystalluria. A synthetic analogue of feline cheek gland pheromones (Feliway™, Sanofi Sante Nutrition Animale, Abbott Laboratories) was then evaluated as a treatment of urine spraying. The study was done on all 34 cats but complete data was obtained for only 22 cats belonging to 19 out of the 24 households. Nine of these cats had abnormalities and/or crystalluria. The results were highly significant: 14 households (74%; 95% confidence interval 49–91%) reported a decrease of spraying frequency.

Insulin as a satiety hormone.

Abstract The effects on food intake of injection of small doses of insulin were investigated in swine. Eleven pigs, 1–3 months of age, weighing 5–50 kg, were fitted with intrajugular catheters. Following a 4-hour fast, insulin (0.03–1.0 U/kg) was injected, and food intake then measured for 10 min. The dose-response curve was U-shaped. The depression of intake at 0.05, 0.13 and 0.25 U/kg was significantly different from control intake, while that after 0.03, 0.5 and 1.0 U/kg was not. The possibility that the release of endogenous insulin may be part of the mechanism of rapid satiety is discussed.

Modification of the responses of sheep to isolation stress by the use of mirror panels

Abstract The behavioural responses of 6 adult Clun Forest wethers were recorded for 105 min while individual sheep were held in an isolation pen in a small hut. The pen was provided with reversible mirror panels so that the animals could be tested under “mirror” and “no mirror” conditions. Blood samples were collected by jugular venepuncture at 15-min intervals during a pre-treatment period when the sheep were housed communally, and also throughout the period of isolation. Plasma concentrations of cortisol and prolactin were measured by radio-immunoassay, and estimations were made of haematocrit and plasma osmolality. Isolated sheep showed considerable interest in the mirror but no other behavioural differences were found. Plasma cortisol levels were increased by isolation and showed evidence of a biphasic response; they were also significantly higher during the “no mirror” condition in the final 45 min. Plasma prolactin concentrations were low and rather variable, but tended to increase gradually in the “no mirror” condition. Isolation produced significant reductions in haematocrit and plasma osmolality, and these effects appeared to be more pronounced in the “no mirror” condition. The results suggest that a variety of factors contribute to the stress response of the isolated sheep, and that a mirror is only partially effective as a substitute for another animal.

The Effect of Enclosure Size on Social Interactions and Daily Activity Patterns of the Captive Asiatic Wild Horse (Equus przewalskii)

Abstract Two herds of Przewalski horses at the Minnesota Zoological Garden were observed during 1980 in each of 2 enclosures that differed in size. The larger enclosure was a 3.4-ha pasture; the smaller enclosure was a 17 × 30-m grass-less pen. One herd was composed of a stallion, 3 adult mares and 2 foals. The other consisted of a stallion and 2 mares. All occurrences of aggression, mutual grooming and snapping were recorded, and 5-min scan-samples of the activity state of each horse were taken. The time budgets, frequency of aggression and frequency of mutual grooming differed significantly with enclosure size for both herds. More time was spent pacing and milling in the smaller enclosure, and the frequency of aggressions and of mutual grooming was also higher. Only the foals exhibited snapping; frequency of snapping did not vary with enclosure size. More time was spent feeding in the larger enclosure. Provision of hay in the smaller enclosure eliminated the differences in time spent feeding. A second study was conducted during the spring of 1984 in an intermediate-sized enclosure, 0.4 ha, a sub-division of the pasture on which the horses were kept in 1980. One herd consisted of a stallion, 2 mares and 2 yearlings; the other consisted of a stallion, 3 mares and a foal. One of the stallions and all of the mares were those studied in 1980, but that stallion and one of the mares were in different herds than they had been in 1980. The frequency of aggression was similar to that observed in 1980.