Neurosecretion in relation to the development of dysdercus fasciatus signoret (Hemiptera : pyrrhocoridae)

• Main Author: Hollebone, Jeannie Elizabeth
• Published: Imperial College London 1968
• Subjects: 571.3
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.623047

Histological examinations of the central nervous system of Dysdercus fasciatus revealed neurosecretory activity throughout nymphal and adult development. Four types of neurosecretory cells, A, B, C and D cells, were described in the pars intercerebralis but largely A cells were observed in other sites of the brain and ventral ganglia. Neurosecretion was not found in the embryo. In the first instar, only A and D cells were observed; B and C cells appeared in subsequent stadia and in adults. The numbers of each cell type increased during development. Two modes of secretion are postulated; neurohaemal release from the corpora cardiaca into the aorta, and direct trans-port through extended axons embedded in the aortal walls to the fat body. Secretory cycles based on histological changes in cell and nuclear volumes and appearance of the neurosecretory product were observed over the following four time intervals of different durations. Stress conditions lasting several hours induced immediate activity in A, B, C and D cells which increased as stress was prolonged. Median neurosecretory cell breis from stressed insects accelerated heart beat. Over twenty-four hours, the onset of light coincided with maximum secretion in A, B and C cells but D cells were unaffected over the daylight period. Peak oxygen consumption coincided with maximum activity of A, B and C cells and implants of median neurosecretory cells and the corpora allata accelerated oxygen consumption. In each instar, maximum synthesis and release in A, B and C cells occurred just before the Mid-intermoult; D cells synthesized continuously but secreted only at the moult. Conelation was observed between neurosecretory activity and changes in the prothoracic glands, epidermis and oxygen consumption of each stadium. The necessity of the median neurosecretory cells for growth and metamorphosis was demonstrated. In adults, maturation of the ovaries in mating females coincided with periods of maximum secretory activity of A, B and C cells. Injection of cysteine-S35 into fourth instar nymphs revealed continuous synthesis and release throughout the stadium of the secretory product in A, B and C cells. Rates and amounts of uptake varied and were characteristic for each cell type. Peak uptake coincided with histologically-defined periods of maximum secretory activity. It is concluded that histological and physiological criteria are useful and complementary methods of assessing neurosecretory activity. The view that all histologically-recognisable cell types occurring in Dysdercus are distinct forms rather than phases of one another is discussed, and the definition of a neurosecretory cell evaluated.