It is most likely that GABA is the neurotransmitter released at the inhibitory LAAV neuromuscular junctions in H.
ACh, but not glutamic acid, caused depolarization of the valve muscle fibers, resulting in decreased flow through the LAA due to contraction of the LAAV. The magnitudes of these effects were similar to those caused by selective stimulation of the LAAV nerve, suggesting cholinergic innervation.
Spontaneous nonspiking oscillations in LAAV muscle membrane potential, with concurrent contraction and relaxation of the valves, were often observed in the present study.
Spontaneous rhythmic contractions of LAAVs were frequently observed in saline-perfused arteries.
The activity of spontaneously contracting LAAVs was modified by both ACh and GABA.
Instead the segmental LAAVs provide the only sites to regulate flow into and through the DAA.
The nerves supplying the LAAVs were first identified in Potamobius astacus by Alexandrowicz (1932a), who referred to them as the nervi segmentales aortae abdominalis.
Flow into the sternal artery would, however, be indirectly reduced if the cardioarterial valves of other arteries and LAAVs were to dilate, lowering the relative flow resistances of other arterial pathways out of the heart.
Apart from the LAAVs of macrurans, very little is known about such peripheral sites of control of hemolymph flow in decapods.
(1997b) supported this hypothesis and suggested in addition that the LAAVs may have been ancestral cardioarterial valves.