Lack of a distinctive behavioural effect of chromogranin-derived peptides in rodents

Chromogranins are neuropeptide precursors stored in large dense core vesicles in which they are processed to smaller peptides. Although these peptides are widespread in the CNS, it is still unknown if they are behaviourally active. For example, even though secretoneurin, a 33-amino acid peptide derived from secretogranin II, was shown to induce release of dopamine from rat striatal neurons, work on the functional significance of this result is still missing. In order to investigate the behavioural effects of chromogranin-derived peptides, we studied the total locomotor activity and rearing behaviour of male albino Sprague-Dawley rats in the open field experimental paradigm. Measurements were performed every 5 min during half an hour before and 2 h after an intracerebroventricular injection of GE-19, GAIPIRRH, secretoneurin or vehicle. None of the tested chromogranin-derived peptides (at a concentration of 20 microM) affected locomotion and rearing behaviour. However, the administration of secretoneurin and GAIPIRRH increased the thigmotaxis, suggesting a possible anxiolytic action. In male Swiss albino mice, which were tested in the black-and-white box paradigm, only GE-19 produced sedation at a dose of 0.72 nmol in 41% of the mice. Overall, there is only little evidence that any of the examined chromogranin-derived peptides produces a behaviourally significant effect, even when given intracerebroventricularly.