Astrocytes Grafted Into Rat Nucleus Basalis Magnocellularis Immediately After Ibotenic Acid Injection Fail to Survive and Have no Effect on Functional Recovery

Abstract

In order to determine if the “trophic” properties of astrocytes makes them appropriate for use as a therapeutic agent to excitotoxic brain damage, adult male rats received grafts of cultured cerebral cortical astrocytes into the NBM immediately after infusion of ibotenic acid into the same structure. Twenty four hours after grafting and every other day for 11 days post surgery, the animals were tested for locomotor activity and habituation in an open field. Animals with NBM lesions had significantly reduced rearing activity as compared to counterparts with no lesions. Nine days after surgery, rats with NBM lesions and astrocyte grafts were as impaired in the acquisition of passive avoidance (PA) as their untreated counterparts. AH animals with ibotenic lesions were impaired on PA retention compared to rats with no lesions. There was no difference between animals that had received grafts and those that had not. Fourteen days after grafting, all brains were processed for Nissl stain, acetylcholinesterase (AChE) histochemistry, GFAP immunocytochemistry, and bisben-zamide fluorescent microscopy. Decreases in the number of neurons in the NBM as well as decreases in the density of AChE staining in the ipsilateral cortex (the area of innervation of the NBM cholinergic neurons) was evident in all animals with NBM lesions. In addition, a large number of host reactive astrocytes were seen within the NBM, its vicinity, and in the ipsilateral neocortex. Grafted astrocytes survived and integrated into the host tissue when they were grafted into the brain of intact animals but no living grafted astrocytes were found in animals injected with ibotenate. In this latter case, two weeks after grafting, instead of surviving astrocytes only fluorescent tissue ‘masses’ were seen in the NBM. surrounded by a cavity. Grafted astrocytes did not have any effect on the extension of the lesion caused by ibotenic acid infusion. These results suggest that the concentration of ibotenic acid used to injure the NBM killed not only the host cholinergic neurons but also the grafted astrocytes. The failure of astrocytes to ameliorate the behavioral deficits caused by ibotenic acid lesions of the NBM may be due to the ibotenic acid creating a lethal environment for the grafted and freshly dissociated, cultured astrocytes.

Key Words:

• Astrocytes
• grafting
• ibotenic acid
• passive avoidance
• behavior