The GT1 GnRH neuronal cell lines exhibit highly differentiated properties of GnRH neurons. We have used GT1–1 cells to study the role of the cyclic AMP/ protein kinase A, cyclic GMP/protein kinase G and Ca2+/protein kinase C signaling pathways in the regulation of GnRH secretion. Superfusion of GT1–1 cells with the cyclic AMP analog 8-Br-cyclic AMP (0.5 and 2.5 mM) or the adenylate cyclase activator forskolin (1 and 10 µM) for 100 min increased the amplitude of GnRH secretion 2- to 35-fold. The cyclic GMP analog 8-Br-cyclic GMP (2.5 mM) also stimulated the amplitude of GnRH release from superfused GT1-1 cells, although to a much lesser extent (1.5- to 3-fold). The amplitude of GnRH pulses was also stimulated (5- to 50-fold) by the protein kinase C activator TPA (1 µM). Increasing intracellular Ca2+ with an iono-phore (ionomycin, 1 µM) or by the Ca2+ channel activator Bay K 8644 (10 µM) also stimulated GnRH release, while secretion was markedly decreased and spontaneous pulsatility abolished by the L-type Ca2+ channel blocker methoxyverapamil (10 µM). These results demonstrate that in GT1 cells the protein kinase A, protein kinase G and protein kinase C pathways are functionally coupled to regulation of GnRH secretion. Furthermore, pulsatile GnRH secretion is coupled to the entry of extracellular Ca2+ via L-type Ca2+ channels.
Honeybees
Apis mellifera
are important pollinators of wild plants and commercial crops. For more than a decade, high percentages of honeybee colony losses have been reported worldwide. Nutritional stress due to habitat depletion, infection by different pests and pathogens and pesticide exposure has been proposed as the major causes. In this study we analyzed how nutritional stress affects colony strength and health. Two groups of colonies were set in a
Eucalyptus grandis
plantation at the beginning of the flowering period (autumn), replicating a natural scenario with a nutritionally poor food source. While both groups of colonies had access to the pollen available in this plantation, one was supplemented with a polyfloral pollen patty during the entire flowering period. In the short-term, colonies under nutritional stress (which consumed mainly
E. grandis
pollen) showed higher infection level with
Nosema
spp. and lower brood and adult bee population, compared to supplemented colonies. On the other hand, these supplemented colonies showed higher infection level with RNA viruses although infection levels were low compared to countries were viral infections have negative impacts. Nutritional stress also had long-term colony effects, because bee population did not recover in spring, as in supplemented colonies did. In conclusion, nutritional stress and
Nosema
spp. infection had a severe impact on colony strength with consequences in both short and long-term.
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