**Acknowledgements**

striatum (establishing limited interactions with the host as a result). At this point, developing transgenic transplantable cells with pharmacologically inducible properties may be able to accomplish this temporary substitute goal. Initial inefficient support might be maintained during the growth process and this might be progressively and selectively removed as dopa-

Plastic adaptation was described above as representing a multitude of cellular responses that occur with the apparent role of maintaining cellular homeostasis, yet within the nervous system also support the maintenance of a sort of dynamic status quo in which compensatory changes adjust the actions or response capacities of local healthy neurons in support of a superseding circuit-associated need. We understand that various CNS circuits establish the capacity to process a wide range of information with various degrees of versatility that presumably evolved to provide stability in some areas of common reliance and flexibility in areas where learning functions occur regularly and synaptic adjustments are correspondingly at higher demand. Neurons appear to undergo adaptations as they attempt to enter a circuit, and the environmental guidance for the control contributed by new additions extends to various degrees backward into the history of the newly added cells in question as it signals what it can provide and encourages host connections while it negotiates for acceptance into the host circuit and the privilege of contributing. As neurons do this during development, their relative pluripotency diminishes toward the eventual niche they enter into and it is highly likely that new neuronal contributions transplanted into these circumstances go through similar steps as they adapt to the roles they play. The long-term viability of additions requires that a utility anticipated by the circuit is fulfilled or the host circuit may adapt the addition out of relevance like an efficient social system isolates and eventually eliminates an influence perceived as disruptive. As an example, a long-term neurotransmitter lingering without dynamic change could come from leaky or malfunctioning neurons, so it would benefit a circuit to recognize this and diminish postsynaptic responses until the signal once again exceeds noise. Synaptic negotiation during development of the mammalian neuromuscular system, which has been more accessible and easier to manipulate with experiments, shows a series of back and forth messages that eventually culminate in the muscle fiber accepting one motoneuron terminal and rejecting other applications for the job (see [195] for detailed discussion of this process). It is likely that whether neurons incorporate into CNS circuits depends upon their capacity to apply themselves and on whether the corresponding job has already been taken, as indicated by the diminished success of transplants into adult intact CNS structures achieving synaptic incorporation. While it is possible for neuronal precursors to be conditioned in a manner that promotes certain wanted phenotypes, the ability to properly incorporate into a workable circuit is challenged when they are placed into an ectopic environment as described above. To draw an analogy to human socialization, it's as if the cells in question either have, or are given, an agenda that may or may not merge with the agenda of the local host circuit. The mechanisms in place that promote apoptosis, in this context, are a useful and positive contribution to the overall circuit despite the fact that the death of cells seems unfortunate. Neurons in various deteriorative diseases adopt abnormal activities. In fact, the whole basis

minergic growth from homotypic regions reaches the area.

**5. Concluding remarks**

30 Neuroplasticity - Insights of Neural Reorganization

Support for this work was provided by the Central Michigan Neuroscience Program, the Central Michigan University Office of Research and Sponsored Programs, the John G. Kulhavi Professorship, and the Field Neurosciences Institute.
