Abstract:
Cyclic glycine-proline (cGP) is a natural nutrient of breast milk and plays a role in regulating the
function of insulin-like growth factor-1 (IGF-1). IGF-1 function is essential for post-natal brain
development and adult cognitive function. We evaluated the effects of cGP on spatial memory
and histological changes in the hippocampus of the adult rats following infancy administration.
Infant rats were treated with either cGP or saline between post-natal days 8 and 22 via oral
administration to lactating dams. The spatial memory was evaluated between post-natal days
70 and 75 using Morris water maze tests. The changes of capillaries, astrocytes, synaptophysin
and glutamate receptor-1 were examined in the CA1 stratum radiatum of the hippocampus.
Compared to saline-treated group, cGP-treated group showed higher path efficiency of entry
and lower average heading errors to the platform zone. cGP-treated group also showed longer,
larger and more astrocytic processes, more capillaries and higher glutamate receptor-1
expression. The rats made less average heading error to the platform zone have more
capillaries, larger and longer astrocytic branches. Thus cGP treatment/supplementation during
infancy moderately improved adulthood spatial memory. This long-lasting effect of cGP on
memory could be mediated via promoting astrocytic plasticity, vascularization and glutamate
trafficking. Therefore, cGP may have a role in regulating IGF-1 function during brain development.
