Hippocampal deafferentation: transplantderived reinnervation and functional recovery

A brief review is provided of the capacity of neural tissue transplants to reinnervate the deafferented hippocampus and repair functional deficits induced by the lesion. The techniques for transplantation of solid pieces of embryonic septum, locus coeruleus or raphe nuclei, or tissue suspensions of embryonic septum, to the adult rat hippocampus are described. Such grafts manifest good long-term survival, provide a good reinnervation of the hippocampus that is histochemically and biochemically appropriate and specific, can establish ultrastructural synaptic contacts with the host, and are electrophysiologically active. Rats with septal grafts manifest recovery of the capacity to learn certain aspects of radial 8-arm maze, T-maze alternation and Morris water-maze tasks. Rats with locus coeruleus grafts manifest an amelioration of lesion-induced hyperactivity. It is concluded that neural tissue transplantation provides a powerful new tool in the study of the functional organization of the hippocampus and its various neurotransmitter-specific afferent systems.     

Functional recovery following brain damage: conceptual frameworks and biological mechanisms

Mammals are well known to manifest recovery over time of many functional impairments induced by brain lesions. A brief reveiw is provided of the different conceptual frameworks within which functional recovery has been examined in the literature, and of different neurobiological mechanisms that have been proposed to account for the phenomenon. We observe that these two levels of analysis have frequently been only loosely related. Finally, a newly identified biological mechanism—compensatory collateral sprouting—is described which appears to be closely related to functional recovery in animals with hippocampal lesions, and this is proposed as a powerful new model within which to investigate further the relationship between the phenomenon of functional recovery and its underlying mechanisms.