431. USING THE LIVE RAT STRESS PARADIGM TO INVESTIGATE APPROACH-AVOIDANCE BEHAVIOUR RELEVANT TO PSYCHIATRIC DISORDERS

Abstract Background Chronic stress is a well-known antecedent to the development of mental health disorders, such as depression. Corticotrophin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVNCRH) are known to play a key role in the neuroendocrine response to stress. However, we, and others, have recently shown that the PVNCRH neurons have non-neuroendocrine (synaptic) actions that directly and rapidly alter behaviour, resulting in lasting changes to stress coping and motivation. The contribution of the neural actions of the PVNCRH neurons to disorders such as depression, and how subpopulations of PVNCRH neurons may contribute to depression symptoms such as altered motivation, remains to be determined. Aims & Objectives Establish the live rat stress paradigm to assess changes in motivational conflict behaviours while undertaking neural recordings. Method To investigate the response of PVNCRH neurons, we used double transgenic CRH-cre x GCaMP6f mice to drive selective expression of the calcium indicator GCaMP6f in PVNCRH neurons. GRIN lens were implanted above the PVN, and miniature microscopes (Inscopix) were used to record the activity of individual PVNCRH neurons. To examine approach-avoidance behaviour under motivational conflict and associated neural activity, the live rat stress paradigm was utilised while undertaking both PVNCRH neural recording and video recording. Testing conditions were hungry (16 hours fasting) or sated mice and exposure to live rat or 3D-printed control. Testing was undertaken in a controlled setting whereby an arena was divided into mouse (40x40cm) and rat (20x40cm) areas, separated by a transparent, perforated wall. Mice could access sugar pellets adjacent to the perforated wall and the rat side of the area (approach behaviour) or retreat to a safe "hide" zone away from the perforated wall (avoidance behaviour). Results Creating a lens tract with a 29G needle prior to slow lens implantation limited tissue compression and facilitated deep hypothalamic imaging, with up to 25 neurons simultaneously recorded in individual animals. Results indicated the rat exposed fasted animals showed higher approach behaviour, with increased time spent in the feeding zone (subsequently near the live rat) compared to sated animals (41.4%±11.0 vs. 25.7%±14.4) and consumed significantly more pellets (35.0±9.0 vs. 8.0±4.0). Comparatively, fasted animals exposed to the live rat spent less time in the feeding zone than those exposed to the 3D-printed control (41.4%±10.97 vs. 86.9%±7.6) and spent more time avoiding in the hide zone than those exposed to the 3D-printed control (23.7%±11.7 vs. 2.5%±2.5). These results indicate different satiety states motivate approach behaviour towards the live rat as expected. Discussion & Conclusions This work established the use of the live rat stress paradigm as a means of investigating altered approach-avoidance behaviour in models of neuropsychiatric disorders such as depression. Ongoing analysis of neural activity is being used to evaluate how the activity of individual PVNCRH neurons is modulated during approach-avoidance behaviours by satiety state. Future studies will aim to use the recording and testing approaches trialled here in combination with a model of depression, to investigate potential role of the PVNCRH neurons in altered motivation and approach-avoidance behaviour.