Anatomy and innervation of the anterior aorta of Aplysia and the ultrastructure of specialized neuromuscular junctions on vascular smooth muscle

Abstract

The fine structure of the cellular layers and innervation of smooth muscle in the anterior aorta of Aplysia were examined. The inner layer of circular muscle is not innervated but its fibers may be electrically coupled. In contrast, longitudinal fibers in the outer layer are well separated and richly innervated by highly specialized neuromuscular junctions (NMJ). Three distinct types of NMJ are present on this smooth muscle, each identifiable by a set of quantitatively described morphological features including size, degree of contact with sarcolemma, density of active zones, number of mitochondria and vesicular content. The three types of NMJ are likely to arise from the identified serotonergic (RDAAE), cholinergic (RDAAI), and glycinergic (R14) neurons that provide the major known excitatory, inhibitory, and modulatory inputs to this vessel. Each longitudinal muscle fiber is separately innervated by one or more NMJ of each type. Since there are no intercellular junctions between longitudinal fibers, coordination of contractility is clearly a function of the pattern of neural activity. This report further characterizes the rapid and fine control of the vasculature in Aplysia and demonstrates the utility of this preparation for cellular-level studies on the neural control of smooth muscle and neurochemical messengers mediating its activity.

Arterial cells and CNS sheath cells from Aplysia californica produce factors that enhance neurite outgrowth in co-cultured neurons

“…The average widths and lengths of AA myocytes in cell culture approach those observed in histological sections of the intact AA (Price et al 1984). The smaller myocytes found in nerve sheath, including those of the PVCs, contract (in response to motor neuron input) and relax to determine the length of connectives (and peripheral nerves) as the animal alters its body dimensions, for example during locomotion (Umitsu et al 1987).…”

Influences of glycine and neuron R14 on contraction of the anterior aorta of Aplysia.

“…A variety of evidence indicates that glycine acts directly on muscle fibers rather than presynaptically. R14 forms specialized junctions on the muscle fibers, but no contacts between R14 and the terminals of other neurons in the anterior aorta have been observed (PRICE et al, 1984). Glycine does not detectably influence spontaneous EJP amplitude or frequency, contrary to what might be expected for the effect on the transmitter release.…”

“…Electrophysiological confirmation of the area innervated by R14 Recording from and stimulation of nerves in the areas innervated by the major processes of R3-R14 were used to confirm morphological descriptions (PRICE and MCADOO,1979;PRICE et a!., 1984) of those fields. Cell bodies were penetrated with glass micropipettes while simultaneously placing suction electrodes on fine nerves in the wall of the anterior aorta or the large vein that connects the gill and kidney of the Aplysia to its heart.…”

Electrophysiological and anatomical identification of the peripheral axons and target tissues of Aplysia neurons R3-14 and their status as multifunctional, multimessenger neurons

“…R3-14 axons are known to end blindly in the sheaths of the parietovisceral ganglion and branchial nerve (Coggeshall et al, 1966;Frazier et al, 1967;. In addition, R3-14 form blind endings in loose connective tissue and near small hemolymph vessels and lacunae Price et al, 1984). These varicose endings are especially common in the pericardial region .…”