Neuronal and glial response in the rat hypothalamus-neurohypophysis complex with streptozotocin-induced diabetes.

This study was aimed to examine the neuronal and glial response in the hypothalamus and neurohypophysis of rats with streptozotocin-induced diabetes. At various time intervals after induction of diabetes the neurons in the paraventricular- (PVN) and supraoptic- (SON) nucleus showed upregulated arginine vasopressin (AVP) and oxytocin (OXT) immunoexpression, being most pronounced at 2 weeks. Concomitant to this was the hypertrophy of PVN and SON neurons. NMDAR1, which was constitutively and moderately expressed in normal rats, was markedly augmented, being most intense at 4 months. This coincided with the expression of neuronal nitric oxide synthase (nNOS). Contrary to this, the expression of GluR2/3 was progressively downregulated, so that it was hardly detected at 4 months. Both astrocytes and microglia marked by anti-GFAP and OX-42, respectively, appeared activated. In pars nervosa, the projection target of the axon terminals of PVN and SON neurons, massive axons and terminals (Herring bodies) laden with neurosecretions were observed in diabetic rats. Colocalization study showed that the neurosecretions were internalized by activated pituicytes and microglia associated with the axons. The present results suggest that the neurosecretion of PVN and SON neurons is enhanced in diabetes. This is coupled by upregulation of NMDAR1 and nNOS but downregulation of GluR2/3. It is speculated that the glutamate receptors and NO are linked to overactivation of PVN and SON neurons leading ultimately to cell death of some of them. The pituicytes and microglia in pars nervosa would help to modulate the release of neurosecretion.