Role of Neuropeptide S on Behavioural and Neurochemical Changes of an Animal Model of Attention-Deficit/Hyperactivity Disorder

Neuropeptide S (NPS) is a recently discovered peptide signalling through its receptor NPSR, which is expressed throughout the brain. Since NPSR activation increases dopaminergic transmission, we now tested if NPSR modulates behavioural and neurochemical alterations displayed by an animal model of attention-deficit/hyperactivity disorder (ADHD), Spontaneous Hypertensive Rats (SHR), compared to its control strain, Wistar Kyoto rats (WKY). NPS (0.1 and 1 nmol, intracerebroventricularly (icv)) did not modify the performance in the open field test in both strains; however, NPSR antagonism with [^tBu-d-Gly⁵]NPS (3 nmol, icv) increased, per se, the total distance travelled by WKY. In the elevated plus-maze, NPS (1 nmol, icv) increased the percentage of entries in the open arms (%EO) only in WKY, an effect prevented by pretreatment with [^tBu-d-Gly⁵]NPS (3 nmol, icv), which decreased per se the %EO in WKY and increased their number of entries in the closed arms. Immunoblotting of frontal cortical extracts showed no differences of NPSR density, although SHR had a lower NPS content than WKY. SHR showed higher activity of dopamine uptake than WKY, and NPS (1 nmol, icv) did not change this profile. Overall, the present work shows that the pattern of functioning of the NPS system is distinct in WKY and SHR, suggesting that this system may contribute to the pathophysiology of ADHD.