Acetylcholinesterase and inhibitors: effects upon normal and regenerating nerves of the rat.

In peripheral nerves, the function of acetylcholinesterase (AChE) is not related to hydrolysis of acetylcholine. To test for a trophic role, AChE or its inhibitors were administered locally to normal and regenerating nerves of rats. In the normal nerve, neither AChE nor serum albumin affected the cytological pattern of the nerve. BW284c51, a specific inhibitor of AChE, resulted in demyelination, proliferation of Schwann cells and sprouting of axons after 5-7 days. Edrophonium or propidium, other specific inhibitors of AChE, did so to a much lesser extent. Vehicle, and iso-OMPA (inhibitor of pseudocholinesterases) did not affect the cytology of the nerve. Elongation of regenerating axons was evaluated at day 3 post-crush. Native AChE applied distal to the crush reduced the elongation of regenerating axons (- 36%), while serum albumin, heated AChE and filtered AChE did not. BW284c51, edrophonium or propidium enhanced the axonal elongation (33%) when they were administered for 2 days before, but not after, the crush. Iso-OMPA or vehicle administered before or after the crush were not effective. Thus, AChE reduces elongation of regenerating axons, while inhibition of AChE enhances elongation and affects the cytology of the normal nerve as well. We propose that AChE has a trophic role in mammalian peripheral nerves.

Pattern formation in a patch occupancy metapopulation model: a cellular automata approach.

The explicit consideration of space in ecological research is of paramount importance to understand the structure and functioning of ecological systems. In this paper we develop a simple spatially explicit metapopulation model in which colonization is constant and independent of the number of occupied patches (i.e. propagule-rain effect, Gotelli, 1991). Extinction, on the other hand, is modelled as a stochastic process whose intensity depends on the number of occupied patches in the neighborhood of each focal patch. Our model is the CA counterpart of two classical patch occupancy metapopulation models. We analytically prove this by showing that our CA converges to the differential equation in the mean-field approximation. The asymptotic behaviour of the system, expressed as the proportion of occupied patches, agrees with the equilibrium proportion of patches derived by using ODEs. In both models, the existence of a rescue-effect increases the range of extinction and colonization parameters over which the system attains complete occupancy of patches. However, in our model this result is strongly influenced by the degree of coupling among patches and is apparent only for local interactions. With local interactions and particular parameter values of colonization and extinction, self-organized spatio-temporal patterns emerge with a fractal-like clustering, even though the environment is spatially homogeneous. Our results point out that the importance of being spatial and discrete (Durrett & Levin, 1994a) in our model is a result of local interactions.