X-Message-Number: 22837
Date: Thu, 13 Nov 2003 20:20:38 -0800 (PST)
From: Doug Skrecky <>
Subject: Researchers Identify Memory Enzyme

Researchers Identify Enzyme That May Turn Fleeting Experience Into
Lasting Memory

WINSTON-SALEM, N.C. - The enzyme that can help turn a one-time experience
into a long-term memory has been identified in mice, researchers at Wake
Forest University Baptist Medical Center reported today at the annual
meeting of the Society for Neuroscience in New Orleans. Ashok Hegde,
Ph.D., of Wake Forest described the researchers' work and proposed a
theory for how lasting memories are formed, a process that involves the
enzyme known as protein kinase C.
 "One of the hallmarks of memories that last very long is a close
association with emotion," Hegde said in an interview. Hegde and
colleagues studied female mice, which, with only one exposure at mating,
can later recognize their partner's scent. After mating, a female mouse
exposed to the scent of a strange male will not continue her pregnancy.
But a female exposed to her partner's scent even a month after mating
will continue her pregnancy. This suggests that the female somehow
memorized her partner's scent during the process of mating. "The good
thing about this model," Hegde said, "is that it's simple and robust. The
memory is unambiguous, and it forms after just one event." In Hegde's
model, formation of the lasting memory in the female mouse requires that
olfactory (smell) information about her partner coincide with sensory
information about the mating. The information is carried by separate
pathways, one involving the neurotransmitter glutamate, the other
norepinephrine. Norepinephrine, which is closely related to adrenaline, is
a chemical released in the brain during emotional or exciting situations.
If it does play a role in humans' being able to vividly remember details
of an experience from decades ago--where people were when they heard news
of President Kennedy's assassination, for example--the question for
researches is how. "There is a threshold for memory storage," Hegde said.
"The brain has to decide what is important for long-term storage. We're
trying to understand how norepinephrine leads to strong-memory
formation." When a memory is formed, structural changes take place at
synapses, the connections between nerve cells. Proteins synthesized by
genes in the nerve cells cause these changes. Generally speaking, the
stronger the connections among synapses, the more lasting the memory.
Hegde and his colleagues--Jian Mu, M.D., Dwayne W. Godwin, Ph.D., and
Chenghai Dong, M.D., Ph.D., all of the Department of Neurobiology and
Anatomy--collected data from the mouse brain to suggest how
norepinephrine serves as a "gatekeeper" to allow memories to form under
certain circumstances. Their research suggests that the enzyme protein
kinase C plays a fundamental role in turning the female's experience of
mating into a long-term memory of her partner's scent. Protein kinase C
activates genes to express certain proteins. How protein kinase C is
linked to gene expression in nerve cells is the subject of a related study
by Cristian Skinner, a graduate student in the Hegde lab.
"We've known for a long time that you need gene expression to launch
protein synthesis, which is necessary to change the synaptic connections
that underlie memory," Hegde said. "This could help look at how genes
work to form new connections among synapses." In collaboration with Josyf
Mychaleckyj, D.Phil., of the Wake Forest Center for Human Genomics, Hegde
said, the human and mouse genomes--both of which have been completely
sequenced--are systematically being searched discover genes that have a
critical role in long-term memory. Also, Hegde and his assistant, Thuy
Smith, are using gene chips that can screen thousands of genes at the
same time to identify the "memory" genes in mice. "The details might be
different in mice and people," Hegde said, "but we think the mechanism
will be the same."

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