We have previously demonstrated the working-heart brainstem mouse preparation to the society (Paton 1996). This preparation has the upper thoracic spinal cord and associated sympathetic nerves. We have also demonstrated the trunk-hindquarters mouse preparation (Chizh et al. 1997)which has the caudal spinal cord and sympathetic outflow but lacks the brainstem, which is crucial for autonomic reflex integration. We have extended these in situ approaches to allow the whole rat to be artificially-perfused (Pickering et al. 2003). This preparation has intact brainstem-spinal cord-effector organ comunication and offers the advantages of access to caudal sympathetic outflows, the potential to monitor changes in organ system function (e.g. kidneys, bladder), a larger vascular tree and more options for peripheral sensory input (eg. hindlimb). Wistar rats (50-150g) were deeply anaesthetised with halothane and the stomach, spleen and the bulk of the large and small bowel ligated and removed through a midline laparotomy. Access to the thoracic cavity was achieved via a midline sternotomy. After immersion in 4°C Ringers solution the animal was either decerebrated or decorticated (for studies of hypothalamic function). The animal was transferred to a recording chamber. A double lumen perfusion cannula was inserted via the left ventricle, through the aortic valve to sit in the first part of the ascending aorta. Carbogenated Ringers (32°C) containing either albumen (2%) or ficoll 70 (1.25%) was anterogradely perfused from a peristaltic pump at a rate of 20-30ml/min. Phrenic nerve activity (PNA) was recorded using a suction electrode. The preparation displayed rhythmic bursts of PNA and respiratory movements within 2 minutes of starting perfusion. The preparation was paralysed (vecuronium 2μg/ml) and the perfusate flow adjusted to obtain an optimal PNA pattern with ramping bursts signalling eupnoea and this was used to judge viability (up to 6 hours). The flow from the pump was computer controlled and can be flexibly adjusted to produce steps or ramps in perfusion pressure. Suction electrode recordings were made of the activity from the thoracic and lumbar chain, the renal, adrenal, mesenteric or splanchnic sympathetic nerves. Access to the brainstem and spinal cord is straightforward for either stimulation or recording. The preparation shows Traub-Hering oscillations in perfusion pressure and also respiratory sinus arrhythmia indicating intact coupling between the brainstem respiratory network, the autonomic outflow and the end organs. All sympathetic outflows show pronounced respiratory modulation. Systemic perfusion pressure ramps demonstrated baroreflex sympathoinhibition. Stimulation of the chemoreflex (NaCN i.a.) evoked a striking increase in sympathetic activity and a corresponding increase in perfusion pressure. Application of a noxious mechanical or thermal stimulus to the hindlimb provokes increases in respiratory rate, perfusion pressure and sympathetic nerve activity. This preparation is relatively quick to establish (30 minutes), permits straightforward access to the central and peripheral autonomic systems, allows excellent control over physiological conditions, has good stability for cellular recordings and provides an intermediate platform between in vitro and in vivo approaches for systems hypothesis testing.