Increased granule cell neurogenesis in the adult dentate gyrus following mossy fiber stimulation sufficient to induce long-term potentiation.

Neurons are continually added at a low rate to the granule cell layer of the dentate gyrus during adulthood in rats. The functional significance of this unusual feature is not completely understood, although recent studies suggest continued granule cell neurogenesis is essential for normal learning and memory. We report here that, in the adult rat, stimulation of the granule cell mossy fibers sufficient to induce long-term potentiation (LTP) increases the number of newly formed granule cells in the dentate gyrus, indicating that granule cell neurogenesis is regulated by efferent activity and, possibly, the induction of LTP.

Effect of winter high temperatures on reproduction and circannual rhythms in hibernating ground squirrels.

We tested whether prevention of hibernation in ground squirrels by midwinter exposure to high ambient temperatures influenced timing of the spring phase of reproductive maturation and the phase and period of subsequent circannual rhythms of reproduction and body mass. Exposing hibernating adult male Spermophilus lateralis to 30 degrees C for 6 weeks beginning December 4 advanced the timing of testicular recrudescence by 4-5 weeks, compared to controls left at 4 degrees C. Males exposed to 30 degrees C for 6 weeks beginning at the average time of spontaneous end of hibernation (January 15) reached reproductive maturation at a time intermediate to those of controls and of the December 4 experimental group. However, neither the date of the subsequent fall's body mass peak, the date of the next year's reproductive maturation, nor the periods of circannual rhythms of body mass and reproduction differed among groups. Premature interruption of hibernation appears to allow early expression of reproduction, but does not affect the underlying timing mechanism.