Making Timid Mice Bold: Loss of Fear Factor
Researchers have identified a fear factor a protein the brain uses to generate one of the most powerful emotions in humans and animals. The molecule is essential for triggering both the innate fears that animals are born with such as the shadow of an approaching predator and fears that arise later in life due to individual experiences. Eliminating the gene that encodes this factor makes a fearful mouse courageous.
Working in mice, the scientists, led by Columbia’s Eric R. Kandel, M.D., University Professor and Howard Hughes Medical Institute investigator, found that the protein stathmin is critical for both innate and learned fear. Mice without stathmin boldly explore environments where normal mice would be hesitant and, unlike their normal counterparts, fail to develop a fear of cues that have been associated with electric shock. The scientists also found physiological changes in the brains of mice lacking stathmin that correlate to the behavioral changes they observed.
“It was localized not only in the pathway of the learning process, but also in the pathway of instinctive fear,” says Dr. Kandel, a 2000 Nobel Prize winner.
The work, published in the Nov. 18, 2005, issue of the journal Cell, was carried out by lead author Gleb Shumyatsky, a postdoctoral fellow from Dr. Kandel’s lab who is now at Rutgers University, and other scientists from Columbia, Rutgers, Harvard, and Albert Einstein College of Medicine.
Both humans and animals are born with an innate fear of certain threatening stimuli. As an example, Dr. Kandel says, “if you see a train heading right at you, you get scared and run away. This is built into the genome the capability to respond to natural threat.” When researchers pair a naturally frightening stimulus, such as an electric shock, with a neutral signal, such as a tone, animals develop fear of the neutral tone. “That is called learned fear that’s acquired, it’s a form of learning.” In humans, stage fright, phobias, and post-traumatic stress disorders are examples of learned fear.
In previous work, Dr. Kandel and his colleagues set out to determine the underlying mechanisms that encode fear in the brain. “We knew from other people’s work about the neural pathways involved but there was little knowledge of the key genes or the detailed neural circuitry involved.”
The researchers began their studies by searching for genes that were particularly active in the amygdala, a region deep within the brain known to contribute to fear and other emotions. They zeroed in on the lateral nucleus, the portion of the amygdala that receives information from the rest of the body about fearful stimuli. They dissected out individual pyramidal cells, the principal cells in the lateral nucleus, and found two genes, known as gastrin-releasing peptide (GRP) and stathmin, that were much more active in the lateral nucleus than in a part of the brain not thought to be involved in fear.
Several years ago, Drs. Kandel and Shumyatsky and their colleagues studied the first of these genes, GRP, in detail and found that it encodes a protein that inhibits the fear-learning circuitry in the brain. GRP does not, however, play a role in innate fear demonstrating that the two fear pathways are genetically distinct.
When the scientists moved on to study stathmin, they had few clues as to what role it might play in fear, if it was involved at all. “When you go after a gene like this, you have no idea what behavior or biological process it may be involved in,” says Dr. Kandel. “I think it’s the mystery of the thing that creates part of the excitement. Except for thinking that the amygdala was very likely to be involved, we had no way of knowing what the outcome would be.”
An indication that stathmin might contribute to fear came when they mapped the parts of the brain where the gene was most active. They found that stathmin was highly expressed in both the amygdala and other parts of the brain’s fear circuitry. “It was localized not only in the pathway of the learning process, but also in the pathway of instinctive fear,” says Dr. Kandel.
To investigate stathmin’s role in more detail, the researchers created mice lacking that gene and examined the brain activity in the lateral nucleus of their amygdalas. Recent work from other labs had shown that during fear learning, the connections between the neurons in this part of the brain strengthen. In stathmin-deficient mice, however, the connections between these neurons remained virtually unchanged, despite repeated stimulation.
These results were good indications that stathmin might play a role in learned fear. To determine whether a lack of stathmin actually altered animal behavior in situations likely to trigger fear, the scientists used several standard laboratory tests. Mice were trained to associate an electric shock with either an auditory tone or a particular location in a cage. After the training period, normal mice would freeze when they encountered the tone or location that they had learned was likely to accompany a shock. Stathmin-deficient mice, on the other hand, seemed unnerved by those stimuli, carrying on their normal activities boldly, without fear.
From these experiments, it was clear to the scientists that stathmin was needed for fear learning. To find out whether it might also contribute to innate fear, the scientists took advantage of mice’s natural fear of open spaces. Unlike normal mice, which cower on the edges of an open field and stay near the center of a plus-shaped maze, mice without stathmin were much more adventurous, readily exploring exposed areas.
The authors concluded from their experiments that stathmin is required for both innate and learned fear. Together with his lab’s previous work on GRP, Dr. Kandel says, the work advances the understanding of learned fear versus instinctive fear in several ways. “It shows genetically there’s a fundamental difference between the two; it gives you some insight into the neural circuitry; it shows that there’s an inhibitory constraint to fear; and it gives you the potential of thinking of therapeutic targets.”
As drug targets, Dr. Kandel says, GRP and stathmin each present unique opportunities. “One would be for learned anxiety, the other would be for instinctive. They both, I think, are reasonable. No one has worked on those as targets before.” While drugs targeting stathmin would likely affect both types of fear, Dr. Kandel expects that with further work researchers should also be able to identify genes that act exclusively on instinctive fear.
Reported by the Howard Hughes
Elderly With Diabetes at Increased Risk for Falling
Falling is the leading cause of accidental death for elderly people, and a new study from Columbia suggests that nursing home residents with diabetes are four times more likely to fall than residents who do not have diabetes.
The study, published in the September 2005 issue of the Journal of Gerontology, found that 78 percent of nursing home residents who had diabetes fell within a 299-day study period; 30 percent of residents without diabetes fell during the same timeframe. The study followed 139 residents of the Hebrew Home in New York’s Riverdale section.
Previous investigations that defined risk factors for falls among frail elderly nursing home residents identified gait or balance disorders, vision impairment, and medications, but diabetes was not widely recognized as a risk factor.
“Our study clearly indicated that nursing homes, assisted living facilities, and others that care for the elderly should consider diabetes a significant risk factor for falling,” says Mathew S. Maurer, M.D., Irving Assistant Professor of Medicine and director of the Clinical Cardiovascular Research Laboratory for the Elderly at New York-Presbyterian Hospital’s Allen Pavilion. “In an era of limited resources, knowing that diabetics are more likely to fall may facilitate identifying older individuals who are likely to benefit from interventions aimed at reducing falls and their consequences.”
Although complications from diabetes include the drop of blood pressure when standing up, known as orthostatic hypotension, and visual impairments, the study found that neither complication explained the increased risk of falling. Dr. Maurer speculates that peripheral neuropathy, a problem with peripheral nerves that can affect the sensation in the feet of diabetics, could be the mechanism responsible for the higher fall rate in residents with diabetes.
New Screen-and-Treat Methods for Cervical Cancer
A study led by Columbia researchers demonstrates the safety and efficacy of two low-tech diagnostic tools to
significantly reduce the prevalence of cervical cancer precursor lesions. Designed as rapid screen-and-treat methods that could be done the same day, the protocols could make prevention of cervical cancer a viable option for all women in any setting around the world.
The two screen-and-treat methods, human papillomavirus (HPV) DNA testing and visual inspection with acetic acid (VIA), followed by treatment using cryotherapy for all eligible women with positive test results, were found to perform as well or better than traditional cytology-based screening (Pap smear) for identifying high-grade cervical cancer precursor lesions. Cryotherapy is a relatively low-technology treatment method that has been shown to be highly efficacious with minimal morbidity. This study was the first time these methods were tested for efficacy in reducing the prevalence of cervical cancer precursor lesions.
“These are highly effective, low-cost methods to reduce the unnecessary mortality from cervical cancer around the world especially in the world’s poorest countries,” says Thomas C. Wright Jr., M.D., professor of pathology and principal investigator of the study. “We found that conducting HPV DNA or VIA protocols in South Africa was not only much more cost-effective than traditional cytology-based approaches, but also similar in overall cost to other well-accepted health interventions, such as childhood vaccines.”
Published in the Nov. 2, 2005, issue of JAMA, the randomized clinical trial included 6,555 nonpregnant women, age 35 to 65 years, between June 2000 and December 2002 at three ambulatory women’s health clinics in Khayelitsha, South Africa. After screening and treatment, the women returned after six and 12 months for follow-up exams. Both the HPV DNA and VIA testing followed by cryotherapy reduced the prevalence of cervical cancer precursor lesions, or CIN 2+. After six months, a 77 percent lower prevalence of CIN 2+ was found among the HPV group compared with a delayed evaluation group and a 37 percent lower prevalence among the VIA group compared with the delayed evaluation group.
“The next step is to conduct large-scale public health intervention projects to better define the operational needs and challenges of these programs,” says Dr. Wright.
Herbs Kill Prostate Cancer Cells
A study has demonstrated that Zyflamend, a unique herbal extract preparation, suppresses the growth of prostate cancer cells and induces prostate cancer cells to self-destruct through apoptosis, or cell death. The research was reported in the October 2005 issue of Nutrition and Cancer.
Zyflamend, a patented formulation, has the ability, in vitro, to reduce prostate cancer cell proliferation by as much as 78 percent and to induce cancer cell death or apoptosis, the researchers reported. The research confirmed that the formulation has COX-1 and COX-2 anti-inflammatory effects, although its anti-cancer effects against prostate cancer were independent of COX-2 inhibition, supporting the idea that some prostate cancer cells are not affected by COX-2 inflammation.
“These results were particularly surprising and show great promise in the fight against prostate cancer,” says Debra L. Bemis, Ph.D., associate research scientist in the Department of Urology. “We hope that the magnitude of benefits shown in this research will be confirmed in the larger scale trial already in progress.”
“We are very encouraged about the early results,” says Aaron E. Katz, M.D., associate professor of urology, director of the Center of Holistic Urology, and principal investigator of the study.
Better Management of Blood Glucose Levels During Heart Surgery
An anesthesiology research team at Columbia completed the first human study to show that aprotinin, a protease inhibitor, lowered blood glucose levels during coronary artery bypass graft (CABG) surgery.
The association of aprotinin with reduced glucose levels during CABG surgery is an important finding for diabetic patients. Of the more than half a million patients who undergo cardiac surgery in the United States every year, one-third of them have diabetes and many others are likely to be obese or suffer from impaired glucose tolerance. For diabetic patients undergoing CABG surgery, abnormally high levels of blood glucose can lead to serious complications including cardiac disease, renal dysfunction, and retina damage as well as an increased risk of infection. For all patients undergoing CABG surgery, elevated glucose levels during the surgery also have been associated with longer hospital stays and increased hospitalization costs.
The research showed that CABG patients receiving aprotinin had 24 percent lower blood glucose levels and a decrease in perioperative insulin resistance compared with patients not receiving aprotinin.
“We are very enthusiastic about these results as our ultimate research goal is to study if aprotinin leads to better outcomes in diabetic patients undergoing CABG surgery,” said Robert J. Frumento, M.S., MPH, lead investigator of the study and a researcher in the P&S anesthesiology department. “The next step will be to conduct a larger, randomized trial on nondiabetic patients before expanding studies to the more vulnerable diabetic patient population. We believe that aprotinin may hold the potential to be a standard of care for patients with diabetes undergoing this surgery.”
The research was presented in October 2005 at the annual meeting of the American Society of Anesthesiologists.