Toxicology and the Nervous System: What You Need to Know
Excerpted with permission from Environmental Health Nursing
The nervous system is highly susceptible to xenobiotic injury because a large number of toxic chemicals, many of which are lipophilic (fat-soluble), target this system. Nerves are composed of fat which predisposes them to damage from these chemicals (Rae, 1996). Because of structural and functional differences within the nervous system, xenobiotics have varied effects, depending on the area of the system targeted by the agent (Marieb, 1995). In order for the body to remain healthy and combat xenobiotic injury, all body systems must be in balance. The nerves innervate organs within every body system and must integrate with the endocrine and immune systems for detoxification to take place. If there is an imbalance in the body systems, the nervous, immune, and endocrine systems become impaired, altering the body’s ability to detoxify (Rae, 1996).
The Blood-Brain Barrier
The blood-brain barrier is a mechanical barrier that protects the nervous system from exposure to toxic substances. It is selective and prevents the passage of metabolic wastes from the blood into the brain tissue. In addition, the brain, spinal cord, and the peripheral nerves are surrounded by special cells that limit the entry of molecules from surrounding tissues. Penetration of xenobiotics and/or their metabolites into the nervous system is largely dependent on their lipid solubility and ability to pass through the membranes that form this barrier (Anthony & Graham et al, 1991; Marieb, 1995).
Maintenance of Lipid-rich Environment
Myelin requires the maintenance of a lipid-rich environment through the metabolism and synthesis of proteins specific to the nervous system. The nerves are composed of fat and are predisposed to damage because many chemicals are lipophilic (Anthony & Graham, 1991). For example, the lipophilic nature of the nerves make them more prone to damage by solvents, compounds that demonstrate high levels in the blood of many patients with environmental illness (Greenberg, 1997; Ma & Chambers, 1994).
Behavioral/Emotional Responses
The behavioral/emotional states encountered in the patient with environmental illness are reproducible by challenge and are therefore not psychosomatic. Rather these problems stem from heightened arousal of the immune system, nervous system, and neuroendocrine systems. An excess of xenobiotics in the body has the ability to:
- Act as neurotransmitters.
- Trigger neurotransmitters.
- Block neurotransmitter production.
- Damage neurotransmitter receptors, causing them to function improperly in a hyperactive manner or not at all.
Chronic and continuous exposure to an incitant may cause symptoms that do not necessarily resolve when the triggering agent is resolved (Stollery & Flindt, 1988; Valciukas et al, 1985).
Cognitive Responses
Common toxic chemicals are known to alter learning. The most common symptoms include recent short-term memory loss, episodic confusion, and poor concentration.
Brain fog is an early symptom of chemical sensitivity. Some impairments are temporary. For example, pesticide exposure results in changes in brain function and learning that can be improved with the removal of the pesticide. Formaldehyde impairs memory that directly affects learning. The effects of formaldehyde exposure can last for days after the initial contact (Rae, 1996).
The patient may make unreasonable decisions after pollutant exposure even though intelligence measures above average. Although the patient normally exhibits adequate problem-solving abilities, these are immobilized after xenobiotic exposure. The patient also demonstrates decreased comprehension and verbalization. Brain function tests show depression of cognitive function, recent memory loss, and loss of ability to remember numbers (Rae, 1996).
Typical Behavioral/Emotional Responses in Environmental Illness
- Angry outbursts
- Anxiety/tension
- Depression
- Disorientation
- Excitability
- Indecisiveness
- Inebriation
- Irritability
- Libido changes
- Loss of confidence
- Panic attacks
- Personality changes
- Sleep disturbance/insomnia
- Restlessness
- Uncontrolled crying
Typical Cognitive Responses in Environmental Illness
- Intermittent confusion
- Decreased alertness (not feeling “sharp”), intellectual functioning, productivity, perceptual accuracy, vigilance
- Lack of focus or concentration: brain fog
- Decreased ability to organize knowledge or evaluate past experiences
- Impaired judgment: memory loss, poor decision making/problem solving
- Speech changes: slurred, slow
Xenobiotic: A xenobiotic is a substance, natural or man-made, that is foreign to the body. An individual is constantly exposed to an array of these substances or toxins during an ordinary day. Constant or even intermittent exposure can result in the accumulation of xenobiotics in the body unless the individual has an effective means of eliminating these compounds…. (Rea, 1992)
