The Journal of Neuroscience, November 1, 2000, 20(21):8144-8152
Using Fos Imaging in the Rat to Reveal the Anatomical Extent of
the Disruptive Effects of Fornix Lesions
Seralynne D.
Vann1,
Malcolm W.
Brown2,
Jonathan
T.
Erichsen3, and
John P.
Aggleton1
1 School of Psychology, Cardiff University, Cardiff,
CF10 3YG, United Kingdom, 2 Department of Anatomy,
University of Bristol, Medical School, Bristol BS8 1TD, United Kingdom,
and 3 Department of Optometry and Vision Sciences, Cardiff
University, Cardiff CF10 3NB, United Kingdom
Activity of the immediate early gene c-fos was compared
across hemispheres in rats with unilateral fornix lesions. To engage Fos production, rats first performed a radial arm maze task that is
severely disrupted by bilateral fornix lesions. Using
immunohistochemical techniques, Fos-positive cells were visualized and
counted in 39 sites in both hemispheres. Fornix lesions led to a
significant reduction in Fos in all ipsilateral hippocampal subfields,
as well as the entorhinal cortex and most of the subicular complex. Other sites that showed reduced activity included the ipsilateral retrosplenial, anterior cingulate, and postrhinal cortices. Subcortical regions showing significant Fos decreases included the anterior thalamic nuclei, supramammillary nucleus, diagonal band of Broca, and
lateral septum. Thus, the effects of fornix lesions extended beyond the
hippocampal formation and included sites not directly innervated by the
tract. These changes were nevertheless selective, as shown by the lack
of hemispheric difference in any of the preselected control sites, the
perirhinal cortex, or nucleus accumbens. Furthermore, there were no
hemispheric differences in an additional group of animals with
unilateral fornix lesions that were killed directly from the
home cage. The location of Fos changes closely corresponded to those
brain regions that when lesioned disrupt spatial working memory.
Moreover, there was a correspondence between those brain regions that
show increased Fos production in normal animals performing the radial
arm maze task and those affected by fornix lesions. These results show
that fornix transection has widespread, but selective, effects on a
network of structures normally activated by spatial memory processes,
with these effects extending beyond the hippocampal formation.
Key words:
amnesia; fornix; hippocampus; immediate early genes; limbic cortices; rat; spatial memory; thalamus
Copyright © 2000 Society for Neuroscience 0270-6474/00/20218144-09$05.00/0
Previous Article | Next Article
