Anatomy and functions of the brain neurosecretory neurons with regard to reproductive diapause in the blow fly Protophormia terraenovae

Abstract

Neural mechanisms controlling endocrine events involved in diapause are poorly understood. This chapter presents a paper in which anatomical study and microlesions of neurons projecting to the retrocerebral complex were performed to examine their possible roles in the induction of reproductive diapause of the female blow fly, Protophormia terraenova. Retrograde-filling through the cardiac-recurrent nerve labeled three groups of neurons in the brain/subesophageal ganglion: paramedial clusters of the pars intercerebralis, neurons in each pars lateralis, and neurons in the subesophageal ganglion. The dendritic arborization of the pars intercerebralis and pars lateralis neurons is restricted to the superior protocerebral neuropil and to the anterior neuropil of the subesophageal ganglion. Retrograde-filling from the corpus allatum indicated that the pars lateralis neurons and a few pars intercerebralis neurons project to the corpus allatum, but that the neurons in the subesophageal ganglion do not. Female adults developed their ovaries under diapause-averting conditions (LD 18:6, 25 °C), whereas their ovarian development was suppressed under diapause-inducing conditions (LD 12:12, 20 °C). Under both conditions, the ovaries invariably failed to develop when the pars intercerebralis was removed. When the pars lateralis were removed bilaterally, the ovaries developed in most of the females, irrespective of the rearing conditions. Removal of the pars lateralis prevented females from entering reproductive diapause. The results show that certain neurosecretory neurons in the pars intercerebralis are necessary for vitellogenesis, and that the pars lateralis contains inhibitory neurons that suppress vitellogenesis during reproductive diapause. The chapter also discusses the neuroendocrine mechanisms controlling reproductive diapause in female. P. terraenovae are discussed compared with those of several other species.