Behavioral, physiological, and neurological influences of pheromones and interomones in domestic dogs
Pirner, Glenna M
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Pheromones provide a crucial method of information transfer for many species; however, this type of communication is not well understood in the domestic dog. Beyond intraspecific communication, evidence suggests that some molecules, known as interomones, may act as a pheromone in one species but elicit unpredictable effects in a different species. 2-methylbut-2-enal (2M2B), the rabbit maternal-neonatal pheromone, is one such molecule. To determine the behavioral and physiological effects of 2M2B on chronically stressed domestic dogs two stress-induction models were used: a simulated thunderstorm and car travel. In both models, 2M2B elicited a faster return of elevated heart rate (HR) to baseline compared to control (CON). During the thunderstorm dogs treated with 2M2B spent 15.9% more time lying down compared to when treated with CON (p = 0.04). Heart rate variability measures, leukocyte differentials, and adrenocorticotropic hormone-stimulation tests were recorded from the dogs used in these studies to understand how acute stressors affect chronically stressed dogs, and how 2M2B might ameliorate this response. Average R-R interval was negatively, but not significantly, correlated with the magnitude of difference in heart rate between placebo and 2M2B ointment during the simulated thunderstorm. There is limited research on domestic dog pheromones, and there are notable inconsistencies in the literature that does exist. To identify urinary volatiles that may act as pheromones, urine was collected from five individuals in each of six groups: juvenile intact male (JIM), adult intact male (AIM), adult castrated male (AXM), juvenile intact female (JIF), adult intact female (AIF), and adult ovariohysterectomized female (AXF). Headspace sampling yielded six molecules with significantly different peak areas between groups. Octanal, 2-methyl-quinoline, methyl propyl sulfide, and 2-heptanone appear to be closely linked to male sex hormones as they had significantly higher peak areas in intact adult males. 3-ethylcyclopentanone appears to be associated with intact adult females and castrated or subordinate male animals. No sex or life stage patterns could be divulged from the data on 2-pentanone. For a molecule to elicit a behavioral or physiological response, it stands to reason that regions of the brain corresponding to the effect should be activated. 5α-androst-16-en-3-one elicits behavioral and physiological effects in women, especially during the time of ovulation. Functional magnetic resonance imaging (fMRI) and blood-oxygen-level dependent (BOLD) contrast were employed to determine which areas of the brain might be responsible for these effects. Ten women received an fMRI scan with ANDRO, 2M2B, rose odor (ROSE), and fresh air (CON) in a 15 s on / 45 s off block design, with three randomized repetitions. ANDRO activated the left insular region compared to CON (p = 0.04). 2M2B elicited activation in the somatosensory association cortex (p < 0.01), premotor cortex (p < 0.01), and Brodmann’s area 8 (p = 0.03) compared to CON. 2M2B also elicited activation in the posterior cingulate and angular gyri compared to ROSE (p < 0.01, both). The insula and amygdala are regions associated with olfactory processing and so were expected. 2M2B elicited activation mainly in motor processing regions, suggesting a motor response to the molecule. Evidence that either molecule activated the hypothalamus, as would be expected by a priming pheromone, was not observed.