Vulnerability of developing brain to undernutrition.

Four questions are addressed: - 1. What are the immediate effects of undernutrition on developing brain likely to be and what are they? 2. Can any general statement be made about vulnerability of developing brain to undernutrition? 3. To what extent are the immediate effects recoverable on refeeding? 4. Do any attenuating or compensatory mechanisms operate? 1. IMMEDIATE EFFECTS: It is worth stating what is almost axiomatic, because it is often forgotten, that undernutrition is likely to affect only those processes which are contemporaneous with it (plus some that follow it). This is borne out by the available evidence. There appears to be little or no destruction of existing structures by undernutrition. 2. GENERAL STATEMENT ON IMMEDIATE EFFECTS: The novel general statement is examined that undernutrition affects the growth rate of all processes contemporaneous with it to the same extent. This is found to have considerable generality. The possible, though perhaps illusory exception of myelination is discussed. Uniform growth restriction gives rise to distorted brain growth through interaction of the timing of different brain growth processes with the timing of undernutrition. 3. EXTENT OF RECOVERY: Recovery is considered in terms of true catch-up: diminution in absolute deficit. The extent of recovery on refeeding varies from none, through partial, to complete, depending on the process under consideration and the timing and severity of the undernutrition. 4. POSSIBLE COMPENSATORY MECHANISMS: Intrinsic to the animal include altered cell cycle characteristics, delayed development, that all of these operate to a greater or lesser extent, during or after undernutrition, thus reducing the magnitude of effects and facilitating recovery.