Neurochemical and electrophysiological diagnosis of reversible neurotoxicity in earthworms exposed to sublethal concentrations of CL-20.
OBJECTIVE
Hexanitrohexaazaisowurtzitane (CL-20) is a relatively new energetic compound sharing some degree of structural similarity with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a known neurotoxic compound. Previously, we demonstrated using a noninvasive electrophysiological technique that CL-20 was a more potent neurotoxicant than RDX to the earthworm Eisenia fetida. In the present study, we investigated the effect of CL-20 exposure and subsequent recovery on muscarinic acetylcholine receptors (mAChRs) to further define the mechanism of reversible neurotoxicity of CL-20 in E. fetida.


METHODS
We used a noninvasive electrophysiological technique to evaluate neurotoxicity in CL-20-treated worms, and then measured how such exposures altered levels of whole-body mAChR in the same animals.


CONCLUSIONS
A good correlation exists between these two types of endpoints. Effect on mAChR levels was most prominent at day 6 of exposure. After 7 days of recovery, both conduction velocity and mAChR were significantly restored. Our results show that sublethal concentrations of CL-20 significantly reduced mAChR levels in a concentration- and duration-dependent manner, which was accompanied with significant decreases in the conduction velocity of the medial and lateral giant nerve fibers. After 7-day post exposure recovery, worms restored both neurochemical (mAChR) and neurophysiological (conduction velocity) endpoints that were reduced during 6-day exposures to CL-20 concentrations from 0.02 to 0.22 microg/cm(2).


CONCLUSIONS
Our findings support the idea that CL-20 induced neurotoxic effects are reversible, and suggest that CL-20 neurotoxicity may be mediated through the cholinergic system. Future studies will investigate other neurotransmission systems such as GABA, glutamate, and monoamine. Ion channels in the nerve membrane should be examined to further define the precise mechanisms underlying CL-20 neurotoxicity.
Gong
Ping
P
SpecPro Inc., 3909 Halls Ferry Road, Vicksburg, MS 39180, USA. ping.gong@us.army.mil
Basu
Niladri
N
Scheuhammer
Anton M
AM
Perkins
Edward J
EJ
D000818:Animals; D001372:Aza Compounds / Q000378:metabolism / Q000633:toxicity*; D015306:Biogenic Monoamines / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology / Q000379:methods*; D004781:Environmental Exposure / Q000009:adverse effects*; D053834:Explosive Agents / Q000378:metabolism / Q000633:toxicity*; D018698:Glutamic Acid / Q000378:metabolism; D006571:Heterocyclic Compounds / Q000378:metabolism / Q000633:toxicity*; D007928:Lethal Dose 50; D020258:Neurotoxicity Syndromes / Q000175:diagnosis / Q000503:physiopathology; D009498:Neurotoxins / Q000378:metabolism / Q000633:toxicity*; D009835:Oligochaeta / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D043587:Receptor, Muscarinic M3 / Q000378:metabolism; D013997:Time Factors; D018675:Toxicity Tests; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
C482139:2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane; D001372:Aza Compounds; D015306:Biogenic Monoamines; D053834:Explosive Agents; D006571:Heterocyclic Compounds; D009498:Neurotoxins; D043587:Receptor, Muscarinic M3; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid