The distribution of catecholamines and beta-endorphin in the brains of three behaviorally distinct breeds of dogs and their F1 hybrids.

This study examines neurochemical and behavioral differences among three types of domestic dogs and F1 hybrids derived from them. Purebred dogs included Border Collies, representing herding dogs, Shar Plaininetz, representing livestock protecting dogs, and Siberian Huskies, representing Northern dogs. Composite behavioral scores were derived from frequency measures of various components of predatory behavior observed when the dogs were tested with mice. Catecholamine levels, including norepinephrine (NE), dopamine (DA), and epineprine (EPI), were determined in various brain regions by high-performance liquid chromatography (HPLC) with electrochemical detection. beta-endorphin levels were determined in the same regions by RIA. Collies showed the highest levels of non-consummatory behaviors and Huskies the highest levels of consummatory behaviors. Shars were found to have lower levels of NE and DA than Collies and Huskies in several brain regions, including those comprising the nigrostriatal DA system. Positive correlations between neurochemical and behavioral characteristics could be made between Shars and Collies. Comparisons of F1 hybrids with their respective parental breeds revealed no clear pattern of inheritance for these characteristics but suggested that multiple factors, both independent and epistatic, are involved. Based on previous studies on nigrostriatal DA and behavior, the levels of DA in this system may be causally related to the levels of predatory behavior expressed by Collies and Shars.