Intracranial injection parameters which affect angiotensin II-induced drinking

Three intracranial injection parameters, injectate concentration at equivalent doses, rupture or bypass of the lateral ventricle by cannula in reaching the site, and multiple injections per animal, were studied to assess their effects on the drinking behavior elicited by angiotensin II at the lateral preoptic area (LPOA). Half of the animals were implanted with 23 gauge cannulae which penetrated the lateral ventricle en route to the site. The remaining animals received cannulae that were angled laterally to bypass the ventricle. In ventricular animals, the more concentrated injectate increased the total water intake over a 30 min period and affected the pattern of drinking through time. Animals with cannulae that penetrated the ventricle en route to the LPOA drank significantly more than the animals whose cannulae missed the ventricle. In all cases, no significant difference in drinking response was found between the first and second injections received by each rat. These results indicate that standardized intracranial chemical injection methods are needed for comparison of experiments utilizing this technique.