The effects of the intracerebroventricular (ICV) administration of crude extracts of lupin quinolizidine alkaloids (LQAs) were studied in adult rat brain tissue. Mature L. exaltatus and L. montanus seeds were collected in western Mexico, and the LQAs from these seeds were extracted and analyzed by capillary gas chromatography. This LQA extract was administered to the right lateral ventricle of adult rats through a stainless steel cannula on five consecutive days. While control animals received 10 microl of sesame oil daily (vehicle), the experimental rats (10 per group) received 20 ng of LQA from either L. exaltatus or from L. montanus. All the animals were sacrificed 40 h after receiving the last dose of alkaloids, and their brains were removed, fixed and coronal paraffin sections were stained with haematoxylin and eosin. Immediately after the administration of LQA the animals began grooming and suffered tachycardia, tachypnea, piloerection, tail erection, muscular contractions, loss of equilibrium, excitation, and unsteady walk. In the brains of the animals treated with LQA damaged neurons were identified. The most frequent abnormalities observed in this brain tissue were "red neurons" with shrunken eosinophilic cytoplasm, strongly stained pyknotic nuclei, neuronal swelling, spongiform neuropil, "ghost cells" (hypochromasia), and abundant neuronophagic figures in numerous brain areas. While some alterations in neurons were observed in control tissues, unlike those found in the animals treated with LQA these were not significant. Thus, the histopathological changes observed can be principally attributed to the administration of sparteine and lupanine present in the alkaloid extracts.