NEUROPHYSIOLOGICAL CORRELATES ASSOCIATED WITH BEHAVIORAL TRAITS IN MINK
A.J.Zanella1* and G.M. Mason2 1Michigan State University, East Lansing,
USA, 2University of Oxford, Oxford, UK.
Captive minks (Mustela vison) often develop stereotypies, which are repetitive
behaviors with no apparent function. Minks selectively bred to be inactive
or to show stereotypies were used in this experiment. Behavior observation
was carried out for 8 weeks. Seventeen males, were chosen for this study
Group A minks (n=6) were selected from the inactive line, and group B (n=6)
minks from the stereotypic line. A group of 5 additional minks (group C)
were removed from a randomly bred population,and showed similar levels
of activity to group B but had no stereotypies. Animals were euthanized
by intraperitonial pentobarbital infusion and blood and brain tissue were
collected 5 minutes post-injection. Cortisol and beta-endorphin levels
were measured in plasma using radioimmunoassay (RIA). White blood cells
(WBC) were isolated, lysed, and intracellular dynorphin levels were monitored
by RIA. Brains were removed and norepinephrine (NE), epinephrine (EP) and
dopamine (DA) levels were monitored in extracts of frontal cortex (FC)
using HPLC. Serotonin levels were measured in FC tissue using ELISA. Stereotypies
were not observed in group A. Group B and Group C performed stereotypies
for 43.8 % and 1.8% of observation time,respectively. Cortisol levels (ng/ml
1 SEM)) were higher in inactive animals (A= 84.37 19.66, B= 31.66 1 11.74
and C= 57.48 111.06) (p=0.01). High stereotypy animals had higher levels
of intracellular dynorphin (pg/mg protein 1 SEM) in WBC than inactive or
control animals (208.9 136.5; 108.38 125.66 and 62.9 15.37,p=0.01). There
was no difference in plasma beta-endorphin, FC NE, EP and serotonin levels
among the studied groups. Inactive animals had higher levels of DA (pg/5g
protein) in the FC than control animals (A=53.82pg 1 12.88; B= 25.98 tissue
1 12.6, and C=3.66 tissue 1 0.45, p= 0.02). High intracellular dynorphin
levels in WBC may reflect the concentration of this opioid peptide in the
brain, and supports previous findings relating modulation of opioid system
in association with abnormal behavior in animals. Further work is necessary
to establish the significance of high DA in the FC and high plasma cortisol
in inactive animals. Understanding the physiological mechanisms associated
with stereotypies in minks may help in the development of objective indicators
of welfare, and could be a useful model to study human neurological disorders
characterized by behavior abnormalities.