Objective: 

Little is known regarding the central action of tachykinins, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) on ventilation in fishes. Therefore, this study was carried out to investigate in our experimental model, the unanesthetized rainbow trout Oncorhynchus mykiss whether these neuropeptides are involved centrally in the control of ventilation.

Methods: 

In group 1 trout, we investigated the effects of intracerebroventricular (ICV) administration of vehicle (0.5 ml, = 16) or 25–100 pmol (in 0.5 ml) of trout neuropeptide gamma (NPg, n=8–9), substance P (SP, n=8–10), neurokinin A (NKA, n=7–10). Group 2 trout were injected ICV with vehicle (n=16), trout PACAP (n=8–11) and also VIP (n=8–11). Buccal ventilatory pressure was used to calculate ventilation frequency (VF) and ventilation amplitude (VA).

Results: 

ICV vehicle, SP and NKA were without effect on the ventilatory parameters but NP gamma evoked a significant (P < 0.05) and dose-dependent elevation of VF but a reduction of VA. The net effect of NP gamma was to produce an hypoventilatory response since the total ventilation (VTOT=VF*VA) was significantly reduced by 60% at a dose of 100 pmol. In contrast, only PACAP significantly elevated VF and VA, but PACAP and VIP significantly increased VTOT. At a dose of 100 pmol, PACAP and VIP increased VTOT by 300% and 100% respectively. Intra-arterial injections of NP gamma, SP, NKA, PACAP or VIP were without any effect on the ventilatory variables.

Conclusions: 

Our results suggest that endogenous central NP gamma, PACAP and VIP are components of a cocktail of brain neuropeptides that are differentially implicated in the neuroregulatory control of ventilation in fish.