The effects of cadmium chloride on organotypic cultures of rat sensory ganglia. A light and electron microscope study

Re-evaluation of acute neurotoxic effects of Cd2+ on mesencephalic trigeminal neurons of the adult rat

The mechanism of Cd2+ neurotoxicity, which is considered to be secondary to changes in blood vessels, was re-evaluated in dissociated mesencephalic trigeminal (Me5) neurons of the adult rat. Cd2+ induced morphological changes in Me5 neurons at 0.1 and 1 mM but not at 0.01 mM. The changes appeared predominantly in the cytoplasm: destruction of the cytoplasmic organelles, swelling and vacuolization of the cell body, and finally resulted in cell lysis. These observations indicate necrosis rather than apoptosis, and no sign of degraded nuclear DNA, characteristic to apoptosis, was detected by the TUNEL technique. Using a Ca2+-sensitive dye Indo-1, Cd2+ was found to elevate the intracellular Ca2+ concentration [Ca2+](i) (both in the cytoplasm and the nucleus). Both the elevation in [Ca2+](i) and the morphological alteration were inhibited either by removing Ca2+-from the bathing medium or by the application of BAPTA/AM (10 microM), a membrane-permeable intracellular Ca2+ chelator. Furthermore, neither morphological changes nor elevation in [Ca2+](i) by Cd2+ occurred in the presence of Zn2+. It is concluded that (1) Cd2+ can directly affect nerve cells, (2) toxicity of Cd2+ on Me5 neurons is mediated by continuous elevation in [Ca2+](i), (3) Cd2+ induces necrotic cell death, and (4) Cd2+ neurotoxicity can be antagonized by Zn2+.

Neurobehavioural effects of occupational exposure to cadmium: a cross sectional epidemiological study

BACKGROUND

A patient with unexplained minor behavioural changes associated with an axonal sensorimotor polyneuropathy had a history of chronic occupational exposure to cadmium (Cd). Although animal studies have shown that Cd is a potent neurotoxicant, little is known about its toxicity for the human central nervous system. The aim of this study was to investigate the toxic potential of chronic occupational exposure to Cd on neurobehavioural functions.

METHODS

A cross sectional epidemiological study was conducted ina group of Cd workers and an age matched control group. Eighty nine adult men (42 exposed to Cd and 47 control workers) were given a blinded standardised examination that consisted of computer assisted neurobehavioural tests (neurobehavioural examination system), a validated questionnaire to assess neurotoxic complaints (neurotoxicity symptom checklist--60, NSC-60), and a standardised self administered questionnaire to detect complaints consistent with peripheral neuropathy and dysfunction of the autonomic nervous system. Historical and current data on biomonitoring of exposure to Cd, either the highest value of Cd in urine (CdU in microgram Cd/g creatinine) of each Cd worker during work (CdUmax) or the current value (CdUcurrent) of each control, were available as well as data on microproteinuria.

RESULTS

Cd workers (CdUmax: mean (range), 12.6 (0.4-38.4)) performed worse than the controls (CdUcurrent: mean (range), 0.7 (0.1-2.0)) on visuomotor tasks, symbol digit substitution (p = 0.008), and simple reaction time to direction (p = 0.058) or location (p = 0.042) of a stimulus. In multiple linear regression analysis, symbol digit substitution, simple direction reaction time test, and simple location reaction time test were significantly related to CdUmax, (beta = 0.35 (p < 0.001), beta = 0.25 (p = 0.012), and beta = 0.23 (p = 0.021) respectively). More complaints consistent with peripheral neuropathy (p = 0.004), complaints about equilibrium (p = 0.015), and complaints about concentration ability (p = 0.053) were found in the group exposed to Cd than in the control group, and these variables correlated positively with CdUmax (peripheral neuropathy: beta = 0.38, p < 0.001; equilibrium: beta = 0.22, p = 0.057; concentration ability: beta = 0.27, p = 0.020).

CONCLUSION

Slowing of visuomotor functioning on neurobehavioural testing and increase in complaints consistent with peripheral neuropathy, complaints about equilibrium, and complaints about concentration ability were dose dependently associated with CdU. Age, exposure to other neurotoxicants, or status of renal function could not explain these findings. The present study also indicates that an excess of complaints may be detected in Cd workers before signs of microproteinuria induced by Cd occur.

Distribution of 109Cd in the nervous system of rats after intravenous injection

The distribution of i.v. injected 109Cd within the nervous system was studied in rats 24 h and 1 week after the injection. Measurements by gamma scintillation showed a high uptake of cadmium in peripheral sensory and autonomic ganglia, whereas the uptake was low in the brain, cerebellum, and spinal cord. The accumulation of cadmium in the sciatic nerve was significantly higher than in the brain and spinal nerve roots, but lower than in ganglia. At autoradiography no labeling was seen in the major part of the brain parenchyma, but an accumulation of the metal was observed in structures outside of the blood-brain barrier (BBB), such as the hypophysis, meninges, choroid plexus and pineal gland. Within the peripheral nervous system (PNS), autoradiography showed accumulation of cadmium in the dorsal root ganglia. The results show that the distribution of 109Cd within the nervous system is correlated to regional variations in vascular permeability, blood vessels of different regions permitting penetration of different amounts of the protein-bound cadmium into the nervous tissues. The accumulation of cadmium in certain nervous structures may have relevance for some of the neurotoxicologic effects of this metal that have been demonstrated in animal experiments.