We have estimated numbers of neurons and glial cells in the dorsal lateral geniculate nucleus (LGN) of BXD recombinant inbred strains of mice. Our aim is to explore genetic mechanisms that match numbers of neurons in the primary visual system. We have exploited cases in the Mouse Brain Library (www.mbl.org). The LGN contains an average of 13,000 projection neurons (8,000 to 20,000, n = 37 cases), 3,300 interneurons, and 11,000 glial cells. The volume of the LGN is ~0.3 mm³ (corrected in vivo estimate). Both neuron and glial cell numbers correlate well with LGN volume (r ~ 0.55, n = 74 sides). Neuron number also correlates with glial cell number (r = 0.47). Retinal ganglion cell (RGC) number correlates with the volume of the LGN (r = 0.37, p = 0.04). The correlation between strain averages of RGC and LGN populations is currently very low (r = 0.1, 19 strains), supporting work of PD Spear and colleagues (1996). Difference in RGC proliferation among mice is controlled in part by a QTL (Neuron number control 1; Nnc1) near the Hoxb cluster on Chr 11. The correlation between allelic differences at this locus and RGC number is 0.72, whereas the correlation between this locus and bilateral LGN volume is only 0.07 (p = 0.37). This indicates that Nnc1 regulates neuron number in the visual system by acting primarily at the level of the retina.

Since 3 July 2000