Firing Activities of Neurosecretory Cells Producing Diapause Hormone and its Related Peptides in the Female Silkmoth, Bombyx mori. I. Lbial Cells

Abstract

There are three known clusters of neurosecretory cells expressing a gene encoding diapause hormone (DH) and four related peptides in the suboesophageal ganglion (SOG) of Bombyx mori. Long-term chronic recordings were made from the axonal tract (NCC-3) of a pair of cells localized in the labial (posterior) neuromere of SOG during pupal-adult development. There was a significant difference in firing activity patterns of the labial neurosecretory cells between diapause-egg and non-diapause-egg producers: labial cells in the former were active throughout pupal-adult development, whereas the same cells in the latter usually maintained an inactive state until the last quarter of pupal-adult development, a time at which a secretion of DH seems to be too late to act on the developing ovary for the induction of diapausing eggs. This observation strongly supports the notion that labial cells release DH and are responsible for determination of embryonic diapause in the silkmoth.

Immunoreactive intensity of FXPRL amide neuropeptides in response to environmental conditions in the silkworm, Bombyx mori

“…At the middle pupal stage, DH levels in the SG and SG-brain complex are markedly decreased in the DEP as compared with those of the NDEP (Kitagawa et al 2005). Furthermore, significant morphological and functional differences in the three neuromeres of the DHPCs have been detected following surgical ablation experiments (Ichikawa et al 1996) and electrophysiology experiments involving changes in firing activity patterns between DEP and NDEP (Ichikawa and Kamimoto 2003;Ichikawa 2003). These results suggest that the SLb is anatomically and functionally different from the SMd and SMx and is specialized for diapause determination.…”

“…Likewise, a significant difference occurs in the firing activity patterns of the SLb between DEP and NDEP and between SLb and other neuromeres in both DEP and NDEP (Ichikawa and Kamimoto 2003;Ichikawa 2003). Furthermore, the surgical ablation of the SLb somata during early pupal stages greatly impairs the Fig.…”

Peptide immunocytochemistry of neurons projecting to the retrocerebral complex in the blow fly, Protophormia terraenovae

“…Further, in the silkmoth Bombyx mori, diapause hormone is produced in a pair of cells located in the medioventral region of the posterior neuromere of the SEG. The axon extends through the brain and into the nervi corporis cardiaci and provides varicose terminal branches in the CC (Ichikawa et al 1995(Ichikawa et al , 1996Ichikawa 2003). The diapause hormone acts on developing oocytes to induce diapause in the resulting embryos (Yamashita 1996).…”

Neural control of gene recruitment in metazoans

“…Induction of production of diapausing eggs in the maternal organism starts with reception of the external stimuli by exteroceptors, their conversion into trains of electrical signals and their processing in neural circuits in the brain. In the silkworm, Bombyx mori, the processing inactivates a GABA-ergic inhibitory mechanism, thus allowing secretion of a neuropeptide, the diapause hormone (DH), the product of the DH-PBAN (DH-pheromone biosynthesis activating neuropeptide) gene, by a pair of labial secretory neurons in the midline of the subesophageal ganglion (Sato et al, 1994;Ichikawa, 2003;Shiga and Numata, 2007). Axons of these neurons reach corpora cardiaca, from where they release DH in the hemolymph (Ichikawa et al, 1995).…”

“…The first difference observed between the DH-recruiting and DH-nonrecruiting insects is a difference in the firing activity patterns of respective labial neurons: labial neurons in DH-recruiting silkworms were active throughout pupal-adult development, while in DH-nonrecruiting silkworms these neurons were inactive until the last quarter of pupal-adult development (Ichikawa, 2003). This suggests that the epigenetic information encoded in the continued electrical spike trains of labial neurons of DHrecruiting silkworms is responsible for inactivation of the GABA-ergic inhibitory mechanism and for recruitment of DH in the signal cascade for producing diapausing eggs.…”