A study of pyramidal cell axon collaterals in intact and partially isolated adult cerebral cortex.

In an extensive series of experiments summarized more than 40 years ago, Cajal I described degenerative and other changes of pyramidal neurons of the cerebral cortex after severance of their axons. Many pyramidal neurons normally have collateral fibers and many of the fibers extend in recurrent, branching routes to higher cortical layers. Other collaterals have terminations upon nearby elements. The extent of collateral fields was increased if the deefferentation was done in immature brains of cats and dogs. CajaP reported no evidence that such collateral proliferation occurred in the mature or adult brain although he did not say specifically that mature animals were studied. It has been suggested4, s that proliferation of axon collaterals is a possible explanation for developing supersensitivity in undercut or similarly traumatized cerebral cortex. The authors implied that collateral proliferation might promote an increasing amount of neuronal excitability by way of positive feedback circuitry. This report, utilizing the Golgi impregnation method, is a quantitative evaluation of cortical pyramidal cell axon collaterals in 3 types of tissues, intact, undercut, and electrically stimulated undercut. Tentative conclusions were briefly mentioned in a symposium report a.