A possible attenuation of stress-induced increases in striatal dopamine metabolism by the expression of non-functional masticatory activity in the rat.

It is thought that the expression of oral parafunctions may provide an outlet for stress or aggressiveness in man. Stress-induced increases in central noradrenergic neurotransmission are attenuated in rats which are allowed to bite during stress. Striatal dopaminergic neurotransmission is involved in the genesis of parafunctional oral movements in rodents. As tail pinch is the stressor which most clearly provokes non-functional masticatory activity (NFMA), and also increases striatal dopamine (DA) activity in rats, we investigated whether the expression of NFMA during tail pinch could modify the changes in striatal dopaminergic neurotransmission induced by this stressor. Rats were subjected to tail pinch for 5 min, and the duration of the NFMA displayed was recorded. As an index of dopaminergic activity, 3,4-dihydroxyphenylalanine (DOPA) accumulation and DA and 3,4-dihydroxyphenylacetic (DOPAC) contents in both striata were determined by high-performance liquid chromatography. Striatal DOPA accumulation was similarly increased in relation to control, both in rats which did and did not display NFMA during tail pinch. However, the increases in striatal DOPAC contents, reported 24 min after the stress session, were lower in animals which had displayed NFMA. These results provide further evidence in support of the assumption that the expression of parafunctional masticatory activity attenuates the effects of stress on central catecholaminergic neurotransmission.