rat hydroencephaly

Paul Klosen klosen at bani.ucl.ac.be
Sun Apr 24 16:08:01 EST 1994

In article <20988 at blue.cis.pitt.edu>, jtrst4 at vms.cis.pitt.edu wrote:

> Has  anyone encountered rats with hydroencephaly?
> ie, a hollow cortex or very large lateral ventricles?
> Is this a congenital defect? I recently found a rat's brain
> to be very empty and was wondering what it could be from.
> -- 
> John T. Robicheau
> Pharmacodynamic Research Center
> University of Pittsburgh
> Robich at DrugInfonet.Pharm-Epid.Pitt.Edu

We have observed some rats with congenital hydroencephaly in our colony.
Rats with congenital hydroencephaly always showed external malformations
too (large skull, abnormal eyes, we even had one cyclops with
hydroencephaly). Most of these animals die within a few days after birth,
only a few survive into adulthood.
What you describe appears to me a secondary defect. We had animals with
enlarged ventricles and a compressed cortex after brain surgery
(intracerebral and intraventricular injections, mechanical transections of
deep neuronal pathways). Our interpretation of this phenomenon is that it
is probably due to the obstruction of ventricular communications (Loushka
and Monro) by blood clots that were formed during surgery. This will lead
to an increased pressure in the ventricles, which will after some time
develop into enlarged ventricles with a compressed cortex. We could however
never confirm that the ventricular communications are blocked or that the
ventricular pressure was increased. The animals appear otherwise normal
with no apparent behavioural impairment. The defect was only noted upon
dissection of the brain, where often the cortex would "cave in" as soon as
the skull was dissected away.
In over 2000 rats whose brain we have analyzed so far, we have observed
this phenomenon spontaneously only in three young rats which were from the
same litter. They were the only rats that we externally normal with
enlarged ventricles and a compressed cortex without having had brain
If you encouter this phenomenon often after surgery, you should consider
trying to modify your surgical procedure in order to try to minimize the
problem (It worked for me). You should look for ways to avoid extensive
bleeding when working close to the ventricles. If you observe this
phenomenon spontaneously in increasing numbers of rats in your colony, it
may indeed be congenital and you may have excessive inbreeding in your
animals. Try introducing "fresh" genetic material from outside your colony
(if possible of course).

Paul Klosen
Cell Biology Lab., Catholic University of Louvain
klosen at bani.ucl.ac.be

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