Central neurotropic activity of homovanillic acid

In experiments performed on male Wistar rats in was shown that i.v.c. administered homovanillic acid (HVA) in a dose of 50 micrograms exerted an inhibitory effect on the locomotor activity. In this dose HVA potentiated also the cataleptogenic effect of haloperidol and amphetamine-induced locomotor hyperactivity. On the other hand, the higher dose HVA (200 micrograms) increased locomotor activity, potentiated amphetamine-induced locomotor hyperactivity, but antagonized apomorphine-induced stereotypy. HVA in a dose of 50 micrograms enhanced the turnover of dopamine, and in a dose of 200 micrograms the turnover of noradrenaline in rat brain. The obtained results indicate that the effects of HVA on animal behaviour are connected with its action on catecholaminergic systems in the brain, especially on the dopaminergic receptors. The inhibitory effect of small dose of HVA appears to be presynaptic and the stimulatory effect of a high dose of HVA seems to be postsynaptic. Moreover, the experiments with a high dose of HVA suggest that it may act in the central nervous system either by altering the distribution of endogenous monoamines or by mimicking the action of monoamines on specific synaptic receptors.