Search for a gene that may result in fewer neurons in the adult mouse hippocampus

Experimentally produced C57BL/6J- Pdeb rd1 congenic mice carrying this gene for retinal degeneration were previously found to have fewer hippocampal neurons than partner strain C57BL/6J + Pdeb-rdt mice possessing normal retinas. A linked passenger gene on the inserted chromosome segment containing the Pdeb rd1 gene might have been responsible. An inbred strain segregating at the Pdeb rd1 , locus and with a genetic background on which the gene is normally present has now been examined. No neuron loss was observed. These new results indicate that, while Pdeb rd1 was necessary for the occurrence of fewer hippocampal neurons in C57BL/6J- Pdeb rd1 mice, it alone was not sufficient to produce this effect. The Pdeb rd1 gene was acting in combination with at least one other gene not on the introduced chromosome segment. The results also provide evidence that genetic background effects can minimize or eliminate hippocampal neuron loss in some strains that normally carry the Pdeb rd1 gene.