Systematic Analysis of the Cytokine and Anhedonia Response to Peripheral Lipopolysaccharide Administration in Rats
Repeated LPS administration protects against LPS-induced sickness but not anhedonia. After the familiarization phase (data not shown), rats received daily i.p. injections of either 0.63 mg/kg LPS (5 LPS) or vehicle (5 Veh) for 5 consecutive days. Three days after this preexposure phase, an acute systemic injection was administered to rats of either 0.63 mg/kg LPS or vehicle (Veh) and voluntary consumption of water and sucrose was measured during a period of 24 h for 4 days. Repeated peripheral LPS administration reduced body weight during the preexposure phase (a). At the beginning of the test phase, rats preexposed to LPS had a significant lower weight than animals that received vehicle preexposure ( g versus g, ; data not shown). Weight only decreased mildly upon rechallenge with LPS, while weight reduction in LPS naive rats was more pronounced (b). On the first day of the test phase, LPS-challenged rats drank less than their vehicle-injected controls but this effect was less pronounced in rats that were preexposed to LPS (c). Sucrose preference was reduced in LPS-treated rats but no effect of preexposure was found (d). Dashed lines indicate chance level for sucrose preference. Graphs are plotted as mean + SEM ( per group). Data were analyzed by rmANOVA followed by independent samples -test. compared to 5 Veh + Veh, compared to 5 LPS + Veh, and compared to 5 Veh + LPS. 5 Veh + Veh: 5 days of vehicle followed by acute vehicle, 5 Veh + LPS: 5 days of vehicle followed by acute LPS, 5 LPS + Veh: 5 days of LPS followed by acute vehicle, and 5 LPS + LPS: 5 days of LPS followed by acute LPS.