The Toxicology of PCB's—An Overview for Clinicians

Polychlorinated biphenyls (PCB''s) have low acute toxicity but are of public health concern because of their persistence in the environment, the bioaccumulation in human and animal tissues, and their potential for chronic or delayed toxicity.Although many questions remain unanswered, it is clear that occupational exposure, at a minimum, can produce dermatologic effects and liver dysfunction. The long half-life of PCB''s and their presence in various human tissues leaves open the possibility of substantial chronic and delayed effects analogous to those seen in animals. PCB''s are potent inhibitors of reproductive function in both rodents and nonhuman primates and produce liver tumors in animal cancer bioassays. As potent inducers of hepatic enzyme systems, PCB''s may have additional unpredictable long-term health effects.These effects have only recently begun to be studied in a rigorous manner, and although the epidemiological evidence is neither complete nor entirely consistent, there can be no question of the necessity to keep human exposures to the lowest feasible levels.     

Muscle spindles in muscle control

In a previous paper (Inbar, 1972/III) a new adaptive model was proposed for muscular control. According to that scheme muscle spindles (MS) supply continuous information about the system dynamics. In the present study integral pulse frequency modulation (IPFM) is used to correlate MS afferent signals, recorded from frog sartorius muscle, to the same muscle dynamics, in order to establish the feasibility of the proposed MS role in the adaptive muscle model.