Glutamate release from photoreceptor terminals is controlled by
voltage-dependent calcium channels (VDCCs). In humans, mutations in the
Cacna1f gene, encoding the α1F subunit of VDCCs,
underlie the incomplete form of X-linked congenital stationary night
blindness (CSNB2). These mutations impair synaptic transmission from rod
and cone photoreceptors to bipolar cells. Here, we report anatomical and
functional characterizations of the retina in the nob2 (no
b-wave 2) mouse, a naturally occurring mutant caused by a null
mutation in Cacna1f. Not surprisingly, the b-waves of
both the light- and dark-adapted electroretinogram are abnormal in
nob2 mice. The outer plexiform layer (OPL) is disorganized, with
extension of ectopic neurites through the outer nuclear layer that
originate from rod bipolar and horizontal cells, but not from
hyperpolarizing bipolar cells. These ectopic neurites continue to express
mGluR6, which is frequently associated with profiles that label with the
presynaptic marker Ribeye, indicating potential points of ectopic synapse
formation. However, the morphology of the presynaptic Ribeye-positive
profiles is abnormal. While cone pedicles are present their morphology
also appears compromised. Characterizations of visual responses in retinal
ganglion cells in vivo, under photopic conditions, demonstrate
that ON-center cells have a reduced dynamic range, although their basic
center-surround organization is retained; no alteration in the responses
of OFF-center cells was evident. These results indicate that nob2
mice are a valuable model in which to explore the pathophysiological
mechanisms associated with Cacna1f mutations causing CSNB2, and
the subsequent effects on visual information processing. Further, the
nob2 mouse represents a model system in which to define the
signals that guide synapse formation and/or maintenance in the
OPL.