Critical and sensitive periods for reversing the effects of mechanosensory deprivation on behavior, nervous system, and development in Caenorhabditis elegans

In these studies the nematode Caenorhabditis elegans was used as a model to investigate ways to reverse the effects of mechanosensory deprivation on behavior and development. Rose et al. (J Neurosci 2005; 25:7159-7168) showed that worms reared in isolation responded significantly less to a mechanical tap stimulus, were significantly smaller, and expressed significantly lower levels of a postsynaptic glutamate receptor subunit on the command interneurons of the tap response circuit and a presynaptic vesicle marker in the tap sensory neurons compared with worms raised in groups. Here, brief mechanical stimulation at any time throughout development reversed the effects of isolation on the response to tap and on postsynaptic glutamate receptor expression on the command interneurons, suggesting there is no critical period for these measures. In contrast to the high level of plasticity in glutamate receptor subunit expression on the interneurons, low levels of stimulation only rescued vesicle expression in the tap sensory neurons early in development and progressively higher levels of stimulation were required as the worm developed, suggesting a sensitive period immediately after hatching, followed by a period of decreasing plasticity. Stimulation during the first three stages of larval development, but not later, rescued the effects of isolation on worm length, suggesting there is a critical period for this measure that ends in the third larval stage. These results indicate that different effects of early isolation required different amounts and/or timing of stimulation to be reversed.