Genetic differences in brain monoamines level in Pietrain and Duroc pigs exposed to acute restraint stress

Abstract

SummaryThe distribution and endogenous concentrations of norepinephrine (NE), epinephrine (E), dopamine (DA) as well as DA metabolites 3,4‐dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5‐hydroxytryptamine (5‐HT) and the main 5‐HT metabolite – 5‐hydroxyindole‐3‐acetic acid (5‐HIAA), were measured by HPLC in 15 brain areas of control and immobilized adult Duroc (D) and Pietrain (P) pigs. The animals were immobilized for 15, 30 and 60 min in the prone position. Control pigs displayed the pattern of regional distribution of brain monoamines similar to that described in other species. Absolute values of NE and E were much higher in the hypothalamus and the preoptic area of pigs than in other species. The concentration of E was seven times higher in the hippocampus posterior in P pigs as compared to D pigs. Also, in most structures DOPAC/DA ratio was relatively high, which points to strains related difference in the turnover of dopamine. In control animals, statistical differences in the bioamine contents were seen between both strains in 25 cases. Epinephrine accounted for more than 12% of the total concentration of both amines in D and 15% in P, this proportion was the highest among the structures compared. The highest concentration of DA and its metabolites – DOPAC and HVA, was revealed in the caudate nucleus and in the nucleus accumbens. Of other structures, the substantia nigra (SN), the septum and the ventral tegmental area (VTA) contained relatively high concentrations of DA, DOPAC and HVA. The 5‐HT level varied from the lowest concentration in the hippocampus posterior, cornu ammonis, nucleus accumbens and the caudate nucleus to the highest concentration in the hypothalamus, the SN, and brain stem areas. This distribution was paralleled by corresponding concentration of 5‐HIAA, being the highest in raphe nuclei (RN). The most conspicuous changes produced by immobilization stress consisted of a substantial decrease in the hypothalamic levels of NE and E in both strains of pig. The level of NE was always higher in D than in P in cornu ammonis, hippocampus posterior, nucleus caudatus, SN, septum, hypothalamus medialis, tectum and olfactory tuberculum. The same was for E in: SN, septum, hypothalamus medialis, and olfactory tubercle. DA, DOPAC and HVA, were changed primarily in SN in P pigs, and in RN in P and D animals. Serotonin (5‐HT) level increased substantially in RN in P pigs. 5‐HIAA level was highly elevated in the RN being always higher in P than in D pigs and in PAG. We suggest that restraint immobilization stress lead to compensatory changes in both brain monoaminergic systems. These changes may affect coping with stress demands mostly in the structures that are proposed to play a major role in the pig responsiveness to acute stress conditions.