Three‐dimensional architecture of identified cerebral neurosecretory cells in an insect

Abstract

The organization of identified neurosecretory cell groups in the larval brain of the tobacco hornworm, Manduca sexta, was investigated immunocytologically. Computer-assisted three-dimensional reconstruction was used to examine the architecture of the neurosecretory cell groups. The group III lateral neurosecretory cells (L-NSC-III) which produce the prothoracicotropic hormone are located dorsolaterally in the protocerebrum and extend axons medially that decussate to the contralateral lobe prior to exiting the brain through the nervi corporis cardiaci I + II. The group IIa2 medial neurosecretory cells (M-NSC IIa2) are located anteriorly in the medial dorsal protocerebrum. The axons of these cells also exit the brain via the contralateral nervi corporis cardiaci I + II. However, their axons traverse a different pathway through the brain from that of the L-NSC III axons. Each of the cell groups possesses elaborate dendrites with terminal varicosities. The dendrites can be classified into specific fields based upon their location and projection pattern within the brain. The dendrites for these two neurosecretory cell groups overlap in specific regions of the protocerebral neuropil. After the axons of these neurosecretory cells exit the brain through the retrocerebral nerve, they innervate the corpus allatum where they arborize to form neurohemal terminals in strikingly different patterns. The L-NSC III penetrate throughout the glandular structure and the M-NSC IIa2 terminals are restricted to the external sheath. A third group of cerebral neurosecretory cells, the ventromedial neurons (VM) which stain with the monoclonal antibody to prothoracicotropic hormone in Manduca, are located anteriorly in the medial region of the brain. The axons of these cells do not exit the brain to the retrocerebral complex, but rather pass through the circumesophageal connectives and ventral nerve cord. These neurons appear to be the same VM neurons that produce eclosion hormone. One dendritic field of the L-NSC III terminates in close apposition to the VM neurons. The distinct morphologies of these neurosecretory cell groups in relation to other cell groups and the distribution of neuropeptides within the neurons suggest that insect neurosecretory cells, like their vertebrate counterparts, may have multiple regulatory roles.

Gastrin‐cholecystokinin‐like immunoreactivity in the central nervous system of the milkweed bug, Spilostethus pandurus. Ultrastructural aspects of the reactive A cells of the brain

“…The axons of the A-cells first exit towards the anterior and then cross over to the opposite side, and pass in posterior direction until they leave the brain from the posterior side. Recently, a similar pathway has been described using confocal microscopy in the larval brain of the tobacco hornworm Manduca sexta [27]. We particularly noted the presence of large amounts of CCK-like material in the walls of the aorta adjacent to the CC-CA complex, but never in the glands themselves of Spilostethus.…”

Neurons involved in nitric oxide-mediated cGMP signaling in the tobacco hornworm,Manduca sexta

“…1B). The number, location, and projections of these neurons identify them as type II neurosecretory cells (Nihjout, 1975; Westbrook et al, 1991). In some preparations, a pair of weakly stained neurons was revealed lateral to the dorsal–posterior midline in the expected location of type III neurosecretory cells (Fig.…”

Occurrence of a prothoracicotropic hormone-like peptide in the developing nervous system of the honey bee (Apis mellifera L)

“…The presence of a potentially prothoracicotropic peptide in the brain-retrocerebral complex and the ventral ganglia of honey bee (Apis mellifera) larvae and pupae corresponded to the reactivity to an antibody raised against the 30-kDa PTTH of the silkworm, Bombyx mori (Mizoguchi et al, 1990 (Westbrook et al, 1991, and with the corresponding neurons in Bombyx mori (Mizoguchi et al, 1990) is suggested by their localization within the brain, as well as by the fact that they are the only neurons in the dorsal protocerebrum that continually produce a PTTH-like peptide. Timing of appearence of this peptide in the dorsolateral neurons, coincides with increases in the hemolymph ecdysteroid titer (Rachinsky et al, 1990), as well as in prothoracic gland activity in honey bee larvae (Hartfelder, 1993 (Zitnan et al, 1993), and by the recent three-dimensional models of Bombyx PTTH (Noguti et al, 1995 (Gray et al, , 1994 (Tublitz and Sylvester, 1990 .…”

“…has considerably improved our knowledge on the structural organization of these neurons in the neuroendocrine axis of insects (O'Brien et al, 1988;Mizoguchi et al, 1990;Westbrook et al, 1991;Goltzené et al, 1992;Zitnan et al, 1993;Dai et al, 1994), and advanced our understanding of the development of the insect central nervous system (Westbrook and Bollenbacher, 1990 (Bowen et al, 1984). This eventually postpones, apparently by glia-neuron signaling (Hartfelder et al, 1994) (Rachinsky et al, 1990), with differences in ecdysteroid titer reflecting a caste-specific program of prothoracic gland activity (Hartfelder, 1993).…”