X-Message-Number: 12716
Date: Fri, 05 Nov 1999 00:30:51 -0500
From: Jan Coetzee <>
Subject: prozac neurogenesis

The more the merrier

                                                         PROZAC
                                                         stimulates the
                                                         birth of new
                                                         brain cells in
                                                         rats, say
                                                         scientists from

                                                         New Jersey. The

                                                         finding gives
                                                         clues to what
                                                         causes
                                                         depression in
                                                         people, how
                                                         drugs like
Prozac
                                                         relieve it and
                          why the effect takes so long to kick in.

                          Just over a year ago, researchers showed that
people
                          grow new neurons all the time. This overturned
a
                          long-held belief that brain cells, unlike
cells in other
                          parts of the body, are not replaced when they
die.

                          Barry Jacobs and Casimir Fornal at Princeton
                          University put together findings from several
different
                          brain studies. They knew, for instance, that
depressed
                          people have a smaller hippocampus--a structure
that
                          is involved in learning and memory--than
healthy
                          people.

                          They also knew that chronic stress can slow
neuron
                          birth, or neurogenesis, in the brains of
rodents. Stress
                          is thought to contribute to depression. "A
little light
                          went on in my head," says Jacobs. "It just
occurred to
                          me that maybe this is what depression is all
about."

                          Jacobs and Fornal went on to show that
activating one
                          type of receptor for the neurotransmitter
serotonin in
                          rats' brains increased the birth of neurons.
So they
                          decided to see if Prozac, which belongs to a
class of
                          drugs known as selective serotonin re-uptake
                          inhibitors (SSRIs), would have the same
effect. SSRIs
                          prevent serotonin from being mopped up,
leaving
                          more of it around to transmit messages.

                          The team gave daily injections of Prozac to
five rats
                          for 21 days. Five control rats were injected
with
                          saline. During the final 7 days, they also
gave the
                          rats a chemical called BrdU, which labels new
                          neurons. When they examined the rats' brains,
69 per
                          cent more new neurons had appeared in the
brains of
                          the Prozac-treated rats compared with the
controls.

                          Jacobs and Fornal believe that the waxing and
waning
                          of neurogenesis in the hippocampus may be an
                          important factor in explaining why people
slump into
                          depression and why they recover with SSRIs. It
may
                          also explain why Prozac takes several weeks to

                          improve mood. "The time needed for these newly

                          generated cells to mature and make appropriate

                          connections provides an explanation for the
                          'therapeutic lag' in antidepressant therapy,"
Jacobs
                          told the meeting.

                          Jacobs thinks serotonin could also help to
treat other
                          neurological diseases, such as Alzheimer's.
But he
                          cautions that it probably won't be of use to
healthy
                          people: "Their level of neurogenesis might
already be
                          optimal."

                                 From New Scientist, 6 November 1999

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