Five feet of snow fell on Breckenridge, Colorado, during the 33rd Annual Winter Conference on Brain Research (WCBR), held January 22-29, 2000. For most of the more than 600 scientists attending the conference, this was a major benefit. The small meeting size, compared with Society for Neuroscience meetings, which typically have 24,000 people, was a second benefit.

"It's a small meeting that allows direct personal contact between scientists," said Tom Dunwiddie of the University of Colorado Health Sciences Center. "This allows in-depth discussion of specific research issues and more productive interaction, making it a first-rate meeting."

"I've attended the winter brain conference for 22 years." Dunwiddie added, "The first year, as a brand new postdoc, I stayed in a snow cave. I'd only worked for my new boss two weeks, so I couldn't ask him to send me to a meeting, but I really wanted to go."

The program consisted of panels, each with three or four scientists presenting in-depth discussions of selected topics, and workshops, with more informal discussions of current issues.

One panel, organized by James Joseph of the US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, considered factors that predispose the aging brain to deficits in neuronal functions (signal transduction) and in behavioral functions (memory loss). The panel also examined putative nutritional and pharmacological interventions used to prevent neuronal changes and possibly prevent the development of neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's.

One of the more novel presentations at WCBR questioned the hypothesis that the hippocampus loses neurons and synapses with increasing age. Don Ingram of the National Institute of Aging presented a review of stereological studies of the brain that have unseated an old hypothesis: that the hippocampus loses neurons and synapses with increasing age. His analyses of two parts of the hippocampus, the CAI and dentate gyrus, showed no significant age-related change in the number of neurons or synapses in mice. Studies from other labs have confirmed the stability of such counts in rats, monkeys, and Homo sapiens. Ingram presented an alternative theory, that with increasing age:

(1) Neurons shrink and lose dendrites.
(2) Neurons are less metabolically active.
(3) Neuron signal transduction pathways operate less efficiently. Speed of transmission from neuron to neuron decreases, and thus efficiency of communication decreases.

Ingram stated that a general breakdown of the entire signal transduction mechanism accounts for why acetylcholinesterase (AChE) inhibitors are not always effective therapeutics. "They give people an enzyme to prevent AChE breakdown and thus amplify the signal," Ingram said. "But it might not solve the problem completely because the remaining parts of the signal transduction pathway aren't working right."

"It's like being deaf. Someone says, turn up the volume," Ingram continued. "It just doesn't work." Ingram concluded that neuronal loss is not a major factor in brain aging.

Joseph noted that age-related changes in membrane biophysics, in part due to alteration by cholesterol, might contribute to motor deterioration. "Cholesterol moves from the membrane inner leaflet to the outer leaflet," Joseph said. "Membrane fluidity changes and then receptor signaling changes. If you alter the membrane receptor, trafficking will change." He noted that sphingolipids show regional selective alteration in brain aging. This could be important since metabolites of sphingomyelin increase oxidative stress and reduce one of the brain's major antioxidants (glutathione).

As we understand more age-related changes in the nervous system, the next question becomes, Are there interventions which retard or prevent some of the observed changes? Joseph searched for nutritional supplements and natural products that could enhance neuronal function. Blueberries topped the list.

He showed that blueberries, when about one percent of a rat's diet (one cup per day for humans), increase release of dopamine, a neurotransmitter, in the striatum. Spinach and strawberries have a similar effect, but less than blueberries.

Blueberries also protected against damage by inflammatory agents such as tissue necrosis factor-alpha (TNF-alpha). Joseph looked at calcium uptake using 6- and 24-month old cells in culture. Both oxidative stressors (dopamine) and inflammatory agents (TNF-alpha) impaired the cells' ability to regulate calcium. However, if they applied blueberry extract to the cells before applying TNF-alpha, the cell retained its ability to lower its calcium levels. Blueberry extract was most effective, with strawberry next and then vitamin E. He plans to test these nutritional supplements in vivo.

The next panelist, Sue Griffin of the Geriatric Research, Education, and Clinical Center at the McClellan Veterans Affairs Medical Center and the Geriatric Department at the University of Arkansas for Medical Sciences, examined factors that stress or injure neurons - direct injury due to accidents or epilepsy, and age-related wear and tear.

"Stresses to neurons have one thing in common," said Griffin. "Neurons increase their synthesis and translation of beta-amyloid precursor protein (bAPP). This causes release of the secreted fragment of beta-amyloid precursor protein (sAPP) and beta-amyloid (or amyloidogenic fragment). This in turn activates microglia to make more interleukin-1 (IL-1), which then drives further bAPP synthesis." IL-1 also activates astrocytes and induces astrocyte expression of S-100 beta, a neurite growth-promoting factor.

"The amyloidogenic fragment is deposited," said Griffin. "And the S-100 beta is the driving factor for the growth of neurites and the conversion of the amyloid deposit into the diagnostic neuritic plaque, which ultimately results in Alzheimer's disease."

Griffin presented data showing that vitamin E can inhibit the activity of microglia and the accompanying production of IL-1, suggesting that beneficial effects of vitamin E may result from the changed microglial response to neuronal stress.

Mark Smith, of Case Western Reserve University, focused on the epidemiology of AD. "The number one risk factor is old age," said Smith. "You need to be old. The young don't get Alzheimer's." Smith looked at age-related changes in neuronal signal transduction pathways and the cell division cycle.

Smith was surprised to find specific increases in signal transduction components such as cyclin-dependent kinase 7 (CDK7), which are normally associated with the cell division cycle. "These were totally unexpected findings since neurons in the adult brain are terminally differentiated and should not attempt to divide," Smith said.

CDK7 and other cell cycle markers were specific for areas of the brain affected by the disease, and expression during aging paralleled disease susceptibility. Smith suggested that, "Inappropriate reentry into the cell cycle is likely a key event in the neuronal degeneration characteristic of Alzheimer's disease."

He proposed that the neuron is sensitized to reenter the cell cycle, followed by cell cycle arrest and eventual atrophy. During active cell division, organelles proliferate. To test the hypothesis, Smith looked at mitochondrial DNA levels. These increased, which could support the hypothesis of organelle proliferation and active cell division.

A workshop on Thursday evening, "Beta-amyloid and Alzheimer Disease: The X-Files of Brain Research" followed the afternoon panel. This workshop, organized by Smith, took the form of a debate between the pro-beta-amyloid team, Griffin and Jean Lording (Arcos Bioscience and Incyte Pharmaceuticals) and Smith and Rachael Neve (Harvard Medical School).

Griffin's team presented the evidence that beta-amyloid deposition causes the neuronal degeneration seen in AD. Smith's team, on the other hand, questioned the logic behind this assumption. If people with Alzheimer's disease have beta-amyloid, and neuronal loss causes Alzheimer's disease, then can we assume that beta-amyloid causes neuronal loss? "No, we cannot," said Smith. "There is no correlation between beta-amyloid and neuronal death." "Amyloid-beta is very toxic in vitro," continued Smith. "In vivo, it doesn't do much."

Neve presented the alternate hypothesis that AD is a derangement of normal processes. Smith concluded, "APP is important. APP processing is important. But it's not clear that amyloid-beta is important." "We have concentrated on amyloid and tau for too long," said Smith.

The debate did not resolve whether beta-amyloid causes AD. Clearly, we need more research before we answer this question.