However, even if the promotility agent domperidone could be potentially effective, due to its absence of permeation through the blood-brain barrier (BBB) , there is insufficient evidence to recommend its utilization for constipation, as in the case of trimebutine (an enkephalinergic
agonist) and erythromycin (the well-known macrolide antibiotic) .
A quick look at the brain reward cascade (see Figure 1) illustrates the "normal" functioning brain (A) whereby serotonin stimulates enkephalinergic
projections in the hypothalamus, which inhibits GABA (an inhibitory neurotransmitter fine tuning the appropriate release of DA) at the substania nigra, leading to the natural physiological release of DA at the NAc.
These neurons send their axons to enkephalinergic
neurons at the nucleus reticularis paragigantocellularis and nucleus raphe magnus.
Naloxone, an antagonist of enkephalinergic receptors, has been able to stimulate the ovarian growth of both mentioned species (Sarojini et al.
NX: animals fed on pellets enriched with the enkephalinergic antagonist naloxone.
According to these authors, enkephalinergic neurons would directly innervate the neurosecretory cells of CHH in the eyestalks, while the dopaminergic neurons would in turn innervate the enkephalinergic ones.
It is well known that enkephalinergic
pathways play a pivotal role in addictive behavior.