Neurotoxicity of 1,3,5-trinitrobenzene (TNB): Immunohistochemical study ofcerebrovascular permeability

1,3,5-Trinitrobenzene (TNB) is a soil and water contaminant at certain mili tary installations. Encephalopathy in rats given 10 daily oral doses of TNB has been reported. The lesion was bilaterally symmetric vacuolation and mi crocavitation in the cerebellar roof nuclei, vestibular nuclei, olivary nuc lei, and inferior colliculi. The contribution of the blood-brain barrier (B BB) in the genesis of these lesions remains uncertain. One of the main goal s of the present work was to evaluate the functional state of the BBB. Male Fischer 344 rats (five rats/group) were euthanatized after four, five, six , seven, eight, or 10 daily doses of TNB (71 mg/kg). A different set of rat s (five rats/group) was allowed to recover for 10 or 30 days after receivin g 10 doses of TNB. Integrity of the BBB was assessed by immunohistochemical staining for extravasated plasma albumin on paraffin-embedded sections. Ra ts euthanatized after four to eight doses had no lesions, and albumin extra vasation in the susceptible regions of the brain was minimal. Rats receivin g 10 daily doses of TNB had bilaterally symmetric vacuolation and microcavi tation in the cerebellar nuclei, vestibular nuclei, and inferior colliculi in association with multifocal, often confluent foci of extravasated albumi n in susceptible nuclei. Albumin was present in vascular walls, extracellul ar space, and neurons. Immunoreactivity in neurons was of two types: cytopl asmic staining representing pinocytic uptake and homogenous staining of the entire neuron (nucleus and cytoplasm) due to uncontrolled albumin leakage through the damaged cell membrane. In rats allowed to recover for 10 days, the microcavitated foci were infiltrated by glial and gitter cells. Albumin immunoreactivity was present as extracellular granular debris, and neurona l staining (for albumin) was mild. In rats allowed to recover for 30 days, immunoreactivity to albumin was not seen. This study demonstrates that TNB- mediated tissue damage is accompanied by breakdown of the BBB. The presence of vacuolation and associated extravasated serum proteins in TNB-treated r ats is an indication of vasogenic brain edema, which appears to be a critic al event in TNB toxicity. Additional studies are needed to determine the re ason for selective regional vulnerability and brain microvasculature suscep tibility to TNB.