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  • The standard model of stress postulates the activation of

    2022-05-26

    The standard model of stress postulates the activation of both the sympathoadrenomedullary axis and the hypothalamo-pituitary-adrenocortical axis. Long-term activation of either neuroendocrine axes has been shown to be harmful [12]. Short-term activation of the sympathoadrenomedullary axis is used to monitor acute stress responses, while the impact of the parasympathetic part of the ANS in modulating the stress response is often ignored. It was postulated that reduced vagal activity (parasympathetic) would limit physiological and behavioral ability to cope with stress. Therefore, methods measuring vagal tone would provide more insight into individual stress vulnerability and magnitude of the stress response. Heart rate is the net effect of the vagus that slows it down thereby increasing the variability between consecutive beats and the sympathetic nerves that accelerate it. Hence, the variability of consecutive heart beats (HRV) measured using noninvasive ECG would quantify both the vagal and sympathetic activities [37]. The results of this study are in agreement with other published findings, which showed no difference in HRV variables in horses competing in dressage and show jumping but is in direct Bradykinin acetate to results found in assessing mental stress in Warmblood horses where the sympathetic branch of the ANS was activated, as presented by an increased LF component [35]. The vagal tone was reduced as expressed in a decrease of the HF component and consequently, the sympatho-vagal balance (LF/HF) was significantly elevated, reflecting the alteration of the ANS from rest to a highly stressed state [13]. This may reflect the experience level of the horses with the activities in which they were engaged. In the present study, both the reduction in HR demonstrated in horses during time spent engaged in EAAT along with no differences in HRV variables SDNN and LF/HF ratio suggests that the therapy sessions were not perceived as being stressful to the horses. Coupled with no change in plasma cortisol, these findings suggest that in horses experienced with EAAT, the interaction with PTSD veterans did not result in a stress response in agreement with previous studies in experienced show jumping horses [14], [38] and therapeutic riding horses [10], [39]. To our knowledge, this is the first report of the measurement of oxytocin in horses used in EAAT programs. Oxytocin has anti-stress effects by reducing glucocorticoid stress hormones in humans and animals and is associated with increases in parasympathetic function [9]. We found no changes in plasma oxytocin concentrations in horses involved in EAAT with veterans. This lack of change possibly could have been due to the time of blood sampling which occurred at 10 and 30 minutes post-EAAT. Because the half-life of oxytocin is short, it may have cleared the bloodstream by the time our samples were taken. Oxytocin concentrations in dogs and their owners increased after 3 minutes of interaction, where the owner stroked, petted, and talked to their dogs [23], and oxytocin concentrations almost doubled in both humans and dogs after positive interaction whereas cortisol concentrations decreased in humans only [22]. Horses may not respond in the same manner as dogs after interaction with humans. Further research investigating the impact of horse–human interactions on oxytocin is warranted. Animal-assisted interventions have been shown to improve cognitive, psychological, and social functioning, while reducing blood pressure, HR, and levels of anxiety in people. The use of horses to treat mental and emotional human health issues is increasing in popularity [6], and there is mounting evidence in the literature to suggest that exposure to animals may assist the overall response to treatment for people with mental illness [40]. The benefits of EAAT for children and adults with diagnoses including eating disorders [2] substance abuse disorders [41], anxiety, depression, and anger [42], [43] have been documented. The results of the present study show a significant reduction in reported symptoms of overall psychological distress, with the exception of interpersonal sensitivity and phobic anxiety, after veterans participated in EAAT sessions for 5 consecutive days. These results are in agreement with a review of current literature which also reports a reduction in symptoms associated with PTSD in participants previously exposed to trauma who then received animal assisted interventions as part of their comprehensive psychological treatment plan [44]. It was noteworthy that while there were reductions in all symptom clusters of PTSD, only Cluster E Hyperarousal Symptoms were significantly reduced. Although there is currently no published research on the effects of EAAT for veterans with PTSD, the results of the present study are also in agreement with the findings of Earles [45], which demonstrated that EAAT was effective in reducing PTSD symptoms and anxiety in participants who had previously experienced a traumatic event.