We carried out a series of experiments to investigate the effect of RFR exposure on neurotransmitters in the brain of the rat. The main neurotransmitter we investigated was acetylcholine, a ubiquitous chemical in the brain involved in numerous physiological and behavioral functions.
We found that exposure to RFR for 45 min decreased the activity of acetylcholine in various regions of the brain of the rat, particularly in the frontal cortex and hippocampus. Further study showed that the response depends on the duration of exposure. Shorter exposure time (20 min) actually increased, rather than decreasing the activity. Different brain areas have different sensitivities to RFR with respect to cholinergic responses [Lai et al., 1987b, 1988b, 1989a,b].
In addition, repeated exposure can lead to some rather long lasting changes in the system: the number of acetylcholine receptors increase or decrease after repeated exposure to RFR to 45 min and 20 min sessions, respectively [Lai et al., 1989a].
Changes in acetylcholine receptors are generally considered to be a compensatory response to repeated disturbance of acetylcholine activity in the brain. Such changes alter the response characteristic of the nervous system. Other studies have shown that endogenous opioids are also involved in the effect of RFR on acetylcholine [Lai et al., 1986b, 1991, 1992b, 1996.]
Since acetylcholine in the frontal cortex and hippocampus is involved in learning and memory functions, we carried out experiments to study whether exposure to RFR affects these behavioral functions in the rat. Two types of memory functions: spatial “working” and “reference” memories were investigated.
Acetylcholine in the brain, especially in the hippocampus, is known to play an important role in these behavioral functions. In the first experiment, “working” memory (short-term memory) was studied using the radial arm maze. This test is very easy to understand. Just imagine you are shopping in a grocery store with a list of items to buy in your mind. After picking up the items, at the check out stand, you find that there is one chicken at the top and another one at the bottom of your shopping cart. You had forgotten that you had already picked up a chicken at the beginning of your shopping spree and picked up another one later. This is a failure in short-term memory and is actually very common in daily life and generally not considered as being pathological. A distraction or a lapse in attention can affect short-term memory.
This analogy is similar to the task in the radial arm maze experiment. The maze consists of a circular center hub with arms radiating out like the spokes of a wheel. Rats are allowed to pick up food pellets at the end of each arm of the maze. There are 12 arms in our maze, and each rat in each testing session is allowed to make 12 arm entries. Re-entering an arm is considered to be a memory deficit. The results of our experiment showed that after exposure to RFR, rats made significantly more arm re-entries than unexposed rats. [Lai et al., 1994.]
This is like finding two chickens, three boxes of table salt, and two bags of potatoes in your shopping cart.
In another experiment, we studied the effect of RFR exposure on reference memory (long-term memory) [Wang and Lai, submitted for publication]. Performance in a water maze was investigated. In this test, a rat is required to locate a submerged platform in a circular water pool. It is released into the pool, and the time taken for it to land on the platform is recorded. Rats were trained in several sessions to learn the location of the platform. The learning rate of RFR-exposed rats was slower, but, after several learning trials, they finally caught up with the control (unexposed) rats. However, the story did not end here. After the rats had learned to locate the platform, in a last session, the platform was removed and rats were released one at a time into the pool. We observed that unexposed rats, after being released into the pool, would swim around circling the area where the platform was once located, whereas RFR-exposed rats showed more random swimming patterns.
To understand this, let us consider another analogy. If I am going to sail from the west coast of the United States to Australia, I can learn to read a map and use instruments to locate my position, in latitude and longitude, etc. However, there is an apparently easier way: just keep sailing southwest. But, imagine, if I sailed and missed Australia. In the first case, if I had sailed using maps and instruments, I would keep on sailing in the area that I thought where Australia would be located hoping that I would see land. On the other hand, if I sailed by the strategy of keeping going southwest, and missed Australia, I would not know what to do. Very soon, I would find myself circumnavigating the globe.
Thus, it seems that unexposed rats learned to locate the platform using cues in the environment (like using a map from memory), whereas RFR-exposed rats used a different strategy (perhaps, something called ‘praxis learning’, i.e., learning of a certain sequence of movements in the environment to reach a certain location. It is less flexible and does not involve cholinergic systems in the brain).
Thus, RFR exposure can completely alter the behavioral strategy of an animal in finding its way in the environment.
… What is significant is that the effects persist for sometime after RFR exposure. If I am reading a book and receive a call from a mobile phone, it probably will not matter if I cannot remember what I had just read. However, the consequence would be much serious, if I am an airplane technician responsible for putting screws and nuts on airplane parts. A phone call in the middle of my work can make me forget and miss several screws. Another adverse scenario of short-term memory deficit is that a person may overdose himself on medication because he has forgotten that he has already taken the medicine.
Lastly, I like to briefly describe the experiments we carried out to investigate the effects of RFR on DNA in brain cells of the rat. We [Lai and Singh 1995, 1996; Lai et al., 1997] reported an increase in DNA single and double strand breaks, two forms of DNA damage, in brain cells of rats after exposure to RFR. DNA damages in cells could have an important implication on health because they are cumulative. Normally, DNA is capable of repairing itself efficiently. Through a homeostatic mechanism, cells maintain a delicate balance between spontaneous and induced DNA damage. DNA damage accumulates if such a balance is altered. Most cells have considerable ability to repair DNA strand breaks; for example, some cells can repair as many as 200,000 breaks in one hour. However, nerve cells have a low capability for DNA repair and DNA breaks could accumulate. Thus, the effect of RFR on DNA could conceivably be more significant on nerve cells than on other cell types of the body.
Cumulative damages in DNA may in turn affect cell functions. DNA damage that accumulates in cells over a period of time may be the cause of slow onset diseases, such as cancer. … Cumulative damage in DNA in cells also has been shown during aging. Particularly, cumulative DNA damage in nerve cells of the brain has been associated with neurodegenerative diseases, such as Alzheimer’s, Huntington’s, and Parkinson’s diseases.
Since nerve cells do not divide and are not likely to become cancerous, more likely consequences of DNA damage in nerve cells are changes in functions and cell death, which could either lead to or accelerate the development of neurodegenerative diseases. Double strand breaks, if not properly repaired, are known to lead to cell death. Indeed, we have observed an increase in apoptosis (a form of cell death) in cells exposed to RFR (unpublished results).
However, another type of brain cells, the glial cells, can become cancerous, resulting from DNA damage. This type of response, i.e., genotoxicity at low and medium cumulative doses and cell death at higher doses, would lead to an inverted-U response function in cancer development and may explain recent reports of increase [Repacholi et al., 1997], decrease [Adey et al., 1996], and no significant effect [Adey et al., 1997] on cancer rate of animals exposed to RFR.
Understandably, it is very difficult to define and judge what constitute low, medium, and high cumulative doses of RFR exposure, since the conditions of exposure are so variable and complex in real life situations.
Interestingly, RFR-induced increases in single and double strand DNA breaks in rat brain cells can be blocked by treating the rats with melatonin … [Lai and Singh, 1997]. Since it is a potent, free radical scavenger, this data suggest that free radicals may play a role in the genetic effect of RFR. [Lai and Singh, 1998].