Neural regulation of sex-pheromone glands in Lepidoptera

Octopamine modulates the activity of motoneurons related to calling behavior in the gypsy moth Lymantria dispar

A morphofunctional investigation of the different neuronal subpopulations projecting through each of the nerves IV-VI emerging bilaterally from the terminal abdominal ganglion (TAG) was correlated with the octopaminergic activity in the ganglion that controls the ovipositor movements associated with calling behavior in the female gypsy moth Lymantria dispar. Tetramethylrodamine-dextran backfills from nerve stumps resulted in a relatively low number of TAG projections, ranging from 12 to 13 for nerve pair IV, 12 to 14 for nerve pair V, and 8 to 9 for nerve pair VI. Furthermore, as assessed by electrophysiological recordings, a number of fibers within each of these nerves displays spontaneous tonic activity, also when the ganglion is fully disconnected from the ventral nerve cord (VNC). Octopamine (OA) applications to the TAG strongly enhanced the activity of these nerves, either by increasing the firing rate of a number of spontaneously firing units or by recruiting new ones. This octopaminergic activity affected calling behavior, and specifically the muscle activity leading to cycling extensions of the intersegmental membrane (IM) between segments VIII and IX (ovipositor). Our results indicate that in the female gypsy moth the octopaminergic neural activity of the TAG is coupled with extensions and retractions of IM for the purpose of releasing pheromone, where motor units innervated by nerve pair IV appear antagonistic with respect to those innervated by nerve pair V.

The pheromonal gland of Lymantria dispar: morphology and evidence for its innervation

The morphological features of the glandular epithelium that secretes pheromone in the polyphagous pest gypsy moth Lymantria dispar are described by light and electron microscopy. The monolayered gland cells are covered by the folded cuticle of the intersegmental membrane between the 8th and 9th abdominal segments showing neither sites of discontinuity nor distinct openings on its external surface. The cells bear a large, often irregularly shaped nucleus, and contain granules of variable amount and electron-density. These granules are mostly located in the basal compartment of the cytoplasm, in a labyrinthine zone laying on a basement membrane. The apical membrane of the gland cells bear microvilli and cell-cell contact is established by different junctional structures. Nerve fibers enwrapped in glia are found beneath the basement membrane, in close contact with the secretory cells. This latter finding represents the first evidence of the innervation of the pheromonal gland in L. dispar.

Release mechanism of sex pheromone in the female gypsy moth Lymantria dispar: a morpho-functional approach

A morpho-functional investigation of the sex pheromone-producing area was correlated with the pheromone release mechanism in the female gypsy moth Lymantria dispar. As assessed by male electroantennograms (EAG) and morphological observations, the pheromone gland consists of a single-layered epithelium both in the dorsal and ventral halves of the intersegmental membrane between the 8th and 9th abdominal segments. By using the male EAG as a biosensor of real-time release of sex pheromone from whole calling females, we found this process time coupled with extension movements of the ovipositor. Nevertheless, in females in which normal calling behavior was prevented, pheromone release was detected neither in absence nor in presence of electrical stimulation of the ventral nerve cord/terminal abdominal ganglion (TAG) complex. Tetramethylrhodamine-conjugated dextran amine stainings also confirm the lack of any innervation of the gland from nerves IV to VI emerging from the TAG. These findings indicate that the release of sex pheromone from the glands in female gypsy moths is independent of any neural control exerted by the TAG on the glands, at least by way of its three most caudally located pairs of nerves, and appears as a consequence of a squeezing mechanism in the pheromone-producing area.

Neuroendocrine control of pheromone biosynthesis in moths

Prevalent among the Lepidoptera, as in many other insect orders, species-specific pheromones are synchronously produced and released for mate finding. Pheromone biosynthesis activating neuropeptide (PBAN) is a neuropeptide widespread throughout the class Insecta. Although its role in the several different orders of insects has not been fully elucidated, its regulatory role in Lepidopteran pheromone biosynthesis has been strongly implicated. The biosynthesis, gene expression, distribution, and release of PBAN have been studied in several moth species. This review discusses PBAN's mode of action as a pheromonotropic neurohormone at the organism, tissue, and cellular levels. The discussion includes an overview on PBAN structure-activity relationships, its target tissue identification, its putative receptor proteins, and the second messengers involved in signal transduction and the key regulatory enzymes in the pheromone biosynthetic pathway that may be influenced by PBAN. Finally, the review includes a discussion of various mediators and inhibitors of the pheromonotropic action due to PBAN.

Synthesis and biological activity of a photoaffinity-biotinylated pheromone-biosynthesis activating neuropeptide (PBAN) analog

To study the mode of action of pheromone-biosynthesis activating neuropeptide (PBAN) at the receptor level and for receptor purification, we synthesized and tested the biologic properties of a photoaffinity biotinylated PBAN analog N-[N-(4-azido-tetrafluorobenzoyl)-biocytinyloxyl-succinimide (Atf-Bct-NHS-PBAN). The Atf-Bct-NHS-PBAN was separated from unreacted reagent and synthetic Hez-PBAN by high-performance liquid chromatography. Conjugated biotin was detected by using enzyme-linked assay as well as tricine sodium dodecyl sulfate polyacrylamide gel electrophoresis. The biologic activity of purified Atf-Bct-NHS-PBAN was confirmed using both in vivo and in vitro pheromonotropic bioassays. These observations indicate that Atf-Bct-NHS-PBAN is a full agonist of PBAN action in pheromone glands and may be used to study PBAN receptors by employing avidin coupled to various reporter groups.

Neuroanatomy and immunocytochemistry of the median neuroendocrine cells of the subesophageal ganglion of the tobacco hawkmoth, Manduca sexta: immunoreactivities to PBAN and other neuropeptides

The median neuroendocrine cells of the subesophageal ganglion, important components of the neuroendocrine system of the tobacco hawkmoth, Manduca sexta, have not been well investigated. Therefore, we studied the anatomy of these cells by axonal backfills and characterized their peptide immunoreactivities. Both larvae and adults were examined, and developmental changes in these neuroendocrine cells were followed. Processes of the median neuroendocrine cells project to terminations in the corpora cardiaca via the third and the ventral nerves of this neurohemal organ, but the ventral nerve of the corpus cardiacum is the principal neurohemal surface for this system. Cobalt backfills of the third cardiacal nerves revealed lateral cells in the maxillary neuromere and a ventro-median pair in the labial neuromere. Backfills of the ventral cardiacal nerves revealed two ventro-median pairs of cells in the mandibular neuromere and two ventro-median triplets in the maxillary neuromere. The efferent projections of these cells are contralateral. The anatomy of the system is basically the same in larvae and adults. The three sets of median neuroendocrine cells are PBAN- and FMRFamide-immunoreactive, but only the mandibular and maxillary cells are proctolin-immunoreactive. During metamorphosis, the mandibular and maxillary cells also acquire CCK-like immunoreactivity and the labial cells become SCP- and sulfakinin-immunoreactive. Characteristics of FMRFamide-like immunostaining suggest that the median neuroendocrine cells may contain one or more of the FLRFamides that have been identified in M. sexta. The mandibular and maxillary neuroendocrine cells appear to produce the same set of hormones, and a somewhat different set of hormones is produced by the labial neuroendocrine cells. Two pairs of interneurons immunologically related to the neurosecretory cells are associated with the median maxillary neuroendocrine cells. These cells are PBAN-, FMRFamide-, SCP-, and sulfakinin-immunoreactive and project to arborizations in the brain and all ventral ganglia. These interneurons appear to have extensive modulatory functions in the CNS.