Neurosecretory system of the American dog tick, Dermacentor variabilis (Acari: Ixodidae). II. Distribution of secretory cell types, axonal pathways and putative neurohemal‐neuroendocrine associations; comparative histological and anatomical implications

Abstract

Histological observations using specialized techniques reveal neurosecretory cells in 18 centers throughout the rind (cortex) of the central nerve mass or synganglion of Dermacentor variabilis. Many cells contribute to complicated networks of neurosecretory pathways and tracts in pre- and post-esophageal portions of the synganglion. The four types of neurohemal-neuroendocrine associations found in Dermacentor resemble structures found in soft ticks (Argasidae) and in other Arachnida, but are more diverse than those described from any other single species. Neurosecretory terminals are distributed diffusely and in two concentrated associations within the perineurium of the synganglion and major peripheral nerves. Terminals are also distributed in the perineurial layers of lateral segmental organs which lie in the general hemocoel at the level of the pedal nerves. A retrocerebral organ complex surrounds the esophagus at its junction with the midgut. The complex includes dorsal and ventro-lateral lobes (containing neurosecretory terminals and intrinsic secretory cells1 and the proventricular (neurohemal) plexus. This plexus seems to be a modified (concentrated) cardioglial association. Cardioglial associations are also formed by the neurosecretory innervation of vascular walls of the dorsal aorta and circulatory sinuses which envelope the synganglion and major peripheral nerves. Inferential considerations of neurosecretory and endocrine interactions in the Acari are based on these anatomical and histological data which also provide the basis for evolutionary considerations of anatomical relationships and specializations in the neurosecretory systems of other Arachnida.

Serotonin-like immunoreactivity in the central nervous system of two ixodid tick species

“…The distribution of neurosecretory centers in the synganglion of both ixodid (IoVe 1964;Dhanda 1967;Binnington and Tatchell 1973;Chow and Wang 1974;Obenchain 1974a, b;Obenchain and Oliver 1975;Binnington 1983;Prullage et al 1992;Szlendak and Oliver 1992) and argasid (Gabe 1955;Eichenberger 1970;Eisen et al 1973;Roshdy et al 1973;Gabbay and Warburg 1977;Pound and Oliver 1982) ticks has been described using light microscopy and transmission electron microscopy. The number of neurosecretory cell centers ranged from 11 in Ornithodoros moubata (Murray) (Eichenberger 1970) to 24 in Ixodes scapularis Say (Szlendak and Oliver 1992).…”

Tick neurobiology: recent advances and the post-genomic era

“…In Dermacentor variabilis, haemal nerves branching proximally and dorsally from pedal ganglia appear to innervate the vascular sheath. Para-axial branches of the nerves contribute to the lateral plexus and also innervate the coxal muscles, dermal glands and the salivary gland (Obenchain and Oliver 1975). To the posterior, the region contains fused ventral ganglion from where the paired opisthosomal and paraspiracular nerves originate.…”

A TECHNIQUE FOR RECORDING EFFERENT NEURONE ACTIVITY FROM NORMAL AND POISONED CATTLE TICKS [BOOPHILUS MICROPLUS (CANESTRINI)]

“…The presence of the longer duration action potentials typical of those produced by neurosecretory neurones supports morphological evidence for the presence of neurosecretory axons in tick peripheral nerves associated with the lateral nerve plexus (Obenchain and Oliver 1975). The regular nature of the response to stimulation of the synganglion suggests that elucidation of some of the pathways regulating motor neurone activity in the tick might be feasible.…”

“…The relatively fine nerves which branch from main pedal trunks or from the lateral nerves plexus (Obenchain and Oliver 1975;Binnington in preparation) were found to be more suitable than the large pedal nerves. Use of the latter produced records with a poor signal/noise ratio; this may have been due to a large number of fibres or to the presence of muscles which are contained, with the nerve, in a sinus of the circulatory system (Obenchain and Oliver 1976).…”