Vasopressinergic network abnormalities potentiate conditioned anxious state of rats subjected to maternal hyperthyroidism

We have previously reported that a mild maternal hyperthyroidism in rats impairs stress coping of adult offspring. To assess anxiogenesis in this rat model of stress over-reactivity, we used two behavioural tests for unconditional and conditional anxious states: elevated plus maze test (EPM) and Vogel conflict test (VCT). In the latter one, arginine vasopressin (AVP) release was enhanced due to osmotic stress. With the EPM test no differences were observed between maternal hyperthyroid rats (MH) and controls. However, with the VCT, the MH showed increased anxiety-like behaviour. This behavioural difference was abolished by diazepam. Plasma AVP concentration curve as a function of water deprivation (WD) time showed a marked increase, reaching its maximal levels within half the time of controls and another significant difference after VCT. A general increase in Fos expression in hypothalamic supraoptic and paraventricular nuclei (PVN) was observed during WD and after VCT. There was also a significant increase of AVP immunoreactivity in anterior hypothalamic area. A large number of Herring bodies were observed in the AVP containing fibres of MH hypothalamic-neurohypophysial system. Numerous reciprocal synaptic connections between AVP and corticotropin releasing factor containing neurons in MH ventromedial PVN were observed by electron microscopy. These results suggest that a mild maternal hyperthyroidism could induce an aberrant organization in offspring's hypothalamic stress related regions which could mediate the enhanced anxiety seen in this animal model.