Andrew Hemmings

Altered mesoaccumbens and nigro-striatal dopamine physiology is associated with stereotypy development in a non-rodent species

Stress-induced changes in mesoaccumbens dopamine neurophysiology have been associated with the development of stereotypic behaviour in in-bred strains of laboratory rodents. This experiment evaluated whether similar changes are associated with environmentally-induced stereotypic behaviour in a higher-vertebrate species, the horse. D1- and D2-like dopamine receptor densities (B(max)) and dissociation constants (K(d)) were measured in control (n=9) and stereotypy (n=9) horses in the nucleus accumbens, caudate nucleus, putamen, substantia nigra and ventral tegmentum brain regions. Results revealed that stereotypy horses had significantly higher (P<0.05) dopamine D1 and D2 receptor densities (B(max)) in the nucleus accumbens compared to non-stereotypy controls. D1 receptor densities (B(max)) and D2 receptor affinity (K(d)) were also significantly lower in the caudate nucleus brain region of stereotypy horses (P<0.05). No other significant results were observed. These results demonstrate that stereotypy horses have increased activity within the mesoaccumbens dopamine pathway and, thus, that the development of environmentally-induced stereotypy may be associated with changes in motivational systems within the animal.

Causal factors of oral versus locomotor stereotypy in the horse

ABSTRACT Stereotypic behaviors are commonly observed in domestic equids as they are in a range of captive nondomesticated species. Estimates suggest that 19.5%‐32.5% of horses perform a stereotypy. The presence of these behaviors is thought to indicate suboptimal welfare status and can result in secondary physical pathologies, such as colic, ligament strain, and incisor wear. Relatively little is understood about the etiologies of oral and locomotor stereotypies. Seemingly disparate causal factors have been proposed, including gastric pathology, neural adaptation, and genetic predisposition. In this review, we propose a model of causality that presents separate pathways to the development and continuation of oral behaviors such as crib‐biting, compared with locomotor alternatives (i.e., weaving). The word stereotypy has alarmingly negative connotation among horse keepers. Stereotypic behaviors are often viewed as vices, and therefore, a number of horse owners and establishments attempt to physically prevent the behavior with harsh mechanical devices. Such interventions can result in chronic stress and be further detrimental to equine welfare. Stereotypy has been proposed to be a stress coping mechanism. However, firm evidence of coping function has proven elusive. This review will explore management options directed at both prophylaxis and remediation.

The effects of a high starch, cereal- based diet compared to a low starch, fibre-based diet on reactivity in horses

Horses fed on concentrate feeds which contain low starch (7%), show reduced reactivity compared to horses fed an isocalorific diet containing high levels of starch (28%).

Developing a 3-Choice Serial Reaction Time Task for Examining Neural and Cognitive Function in an Equine Model

BACKGROUND Large animal models of human neurological disorders are advantageous compared to rodent models due to their neuroanatomical complexity, longevity and their ability to be maintained in naturalised environments. Some large animal models spontaneously develop behaviours that closely resemble the symptoms of neural and psychiatric disorders. The horse is an example of this; the domestic form of this species consistently develops spontaneous stereotypic behaviours akin to the compulsive and impulsive behaviours observed in human neurological disorders such as Tourettes syndrome. The ability to non-invasively probe normal and abnormal equine brain function through cognitive testing may provide an extremely useful methodological tool to assess brain changes associated with certain human neurological and psychiatric conditions. NEW METHOD An automated operant system with the ability to present visual and auditory stimuli as well as dispense salient food reward was developed. To validate the system, ten horses were trained and tested using a standard cognitive task (three choice serial reaction time task (3-CSRTT)). RESULTS All animals achieved total learning criterion and performed six probe sessions. Learning criterion was met within 16.30±0.79 sessions over a three day period. During six probe sessions, level of performance was maintained at 80.67±0.57% (mean±SEM) accuracy. COMPARISON WITH EXISTING METHOD(S) This is the first mobile fully automated system developed to examine cognitive function in the horse. CONCLUSIONS A fully-automated operant system for mobile cognitive function of a large animal model has been designed and validated. Horses pose an interesting complementary model to rodents for the examination of human neurological dysfunction.

The fermentation of hay and starch when incubated in vitro with faecal inoccula from either normal healthy horses or horses with a history of laminitis

Horses have evolved to consume small, frequent, forage-based meals in a trickle feeding manner. Such diets would typically be high in fibre and low in starch. Domesticated equidae are often meal fed feeds high in non-structural carbohydrates, which can, if fed in large amounts, lead to metabolic conditions such as laminitis. The current study examined the effects of incubating hay and starch, in vitro, with inocula comprising faecal material from either normal healthy horses, or those with a history of laminitis. The extent and rate of degradation was measured using the gas production technique. Substrates were inoculated with faecal slurries from either normal healthy horses, or horses with a predisposition to laminitis (they had suffered laminitis within the last 12 months). Significant differences (P<0.001) in the rate and extent of gas production were found between healthy horses and horses prone to laminitis when breaking down hay. Healthy horses had a significantly higher rate and extent of gas production than laminitics. In contrast, horses with a history of laminitis had significantly higher (P<0.001) gas production profiles when fermenting starch, than healthy horses, suggesting that the bacterial profile collected from these animals was more efficient in the breakdown of starch.

Causal and functional interpretation of mu- and delta-opioid receptor profiles in mesoaccumbens and nigrostriatal pathways of an oral stereotypy phenotype

ABSTRACT Spontaneous stereotypic behaviours are repetitive, compulsive, topographically invariant response patterns commonly observed in captive or domestic animals, which have been linked to dysfunction of basal ganglia input/output pathways. There is evidence that endogenous opioids play a key regulatory role in basal ganglia direct and indirect pathways, but their precise role, both causally and functionally, in spontaneous stereotypic behaviour is unclear. Here we examined the profile of mu‐ and delta‐opioid receptors (density [Bmax] and affinity [Kd]) of basal ganglia structures in stereotypy (n=10) and non‐stereotypy (n=10) animals using a competitive ligand binding approach. Mu receptor densities were significantly higher in the nucleus accumbens (p<0.001), ventral tegmentum area (p<0.001) and caudate nuclei (p<0.001) of stereotypy compared to control animals. No differences were observed for delta Bmax values in any of the brain regions studied (p>0.15). Receptor binding affinity was only found to be significantly different between control and stereotypy animals for mu receptors on the caudate region; (p<0.001). Our findings suggest that increased inhibition (via mu‐opioid receptors) of the indirect (dorsal striatopallidal) pathways are associated with spontaneous stereotypy development. Data also suggested that different types of spontaneous stereotypies (e.g. oral versus locomotor) within or a cross species may have a different neurological basis. This may have important implications for understanding the aetiology and function of these behaviours. In some instances (oral stereotypy), the behaviour may be associated with allostasis, a process that could enhance the reward value of appetitive behaviour performance (as a starting point of stereotypy development).

A natural diet

48 May/June 2013 • equine HealtH