Insulin and glucose administration stimulates Fos expression in neurones of the paraventricular nucleus that project to autonomic preganglionic structures

Insulin and glucose play a key role in the control of body energy homeostasis. However, the anatomical organization of the network of central insulin and glucose sensitive areas is still unclear. In the present study, we used a multiple-labelling technique combining retrograde tracing and Fos-like immunohistochemistry, to analyse the anatomical projections from hypothalamic neurones activated by the combined stimulus of insulin and glucose. After intraperitoneal injections of a bolus of insulin plus glucose, Fos-like immunoreactive neurones were observed in the paraventricular nucleus (PVN), ventromedial and arcuate nuclei, as well as the lateral hypothalamic area. In addition, neurones projecting to the autonomic preganglionic levels in the brainstem and spinal cord potentially involved in the control of glucose metabolism were identified by injections of fluorochrome tracers. Thus, Fluorogold was injected into the intermediolateral cell column of the lower spinal cord and Fast Blue was injected into the dorsal motor nucleus of the vagus. Perikarya of descending neurones were detected chiefly in the dorsal, medial and lateral parvocellular subnuclei and also in the posterior magnocellular subnucleus of the PVN. In contrast, insulin-glucose activated neurones in the PVN were observed mainly in the medial parvocellular and posterior magnocellular subnuclei. Fluorogold/Fos double-labelled neurones were only observed in the ventral zone of the medial parvocellular subnucleus. These data indicate that, within the PVN, there could be neurones responding to insulin-glucose administration, which are involved in the sympathetic control of the classical regulatory structures of body energy homeostasis, such as the liver and pancreas, and which could play a role in the output of the neuronal circuitry controlling food intake.