Table 2.
List of guideline studies both general and especially designed to assess for neurotoxicity.
| Guideline | Study title | When required | Species [1] | Protocol timing | Nonpathology [2] | Histopathology |
| General toxicity assessment | ||||||
| 870.1100 870.1200 870.1300 | Acute oral, dermal, and inhalation toxicity | For all chemicals (inhalation not required for some) | Rat or rabbit | Acute dose to young adults and observations for 14 days | Clinical signs, body weight and mortality | Gross necropsy only |
| 870.3100 870.3150 | Subchronic oral, dermal, and inhalation dosing | For most chemicals | Rat or dog | 90 days dosing starting with young adult | Clinical signs, body weight and hematology, clinical chemistry and urinalysis and mortality | Generally hematoxylin and eosin |
| 870.3700 | Prenatal developmental | For most chemicals | Rat or rabbit | Gestation days 6–16 for rats and 6–18 for rabbits | Clinical signs, body weight, uterine data and pup data and mortality | Gross dissection for visceral and skeletal assessment of the pups |
| 870.3800 | Reproductive | For chemicals with food uses and chronic exposure | Rat | Continuous from premating through gestation, lactation and adults for two generations | Reproductive performance, clinical signs, body weight and mortality, pup growth and development | Necropsy and histopathology of the reproductive organs |
| 870.4100 870.4200 870.4300 | Chronic dosing and carcinogenicity | For chemicals with food uses or where chronic exposure is expected | Rat, dog, and mouse | 6 months for dogs, 18 months of more for mice and 24 months for rats | Clinical signs and mortality | Generally the same as for subchronic |
| Special studies for organophosphate-induced delayed neuropathy | ||||||
| 870.6100 | Acute delayed neurotoxicity for OPIDN | All organophosphate AChE inhibitors | Hen (8–14 months of age) | Single limit dose of 2 gm/kg or near lethal dose (ie, LD50). Atropine can be used to prevent death by AChE inhibition. Must have 6 survivors. Sacrifice at day 21 | Gait assessment neuropathy toxic esterase acetylcholinesterase | Whole body perfusion. Sections of medulla oblongata, spinal cord (rostral cervical, midthoracic, and lumbosacral), and peripheral nerves. “Appropriate” myelin and axon specific stains |
| 870.6100 | Subchronic delayed neurotoxicity for OPIDN | For organophosphate AChE inhibitors when the acute study is inconclusive | Limit dose of 1 gm/kg. Three dose levels required. Establish NOAEL and LOAEL | |||
| Special neurotoxicity assessments in rats* | ||||||
| 870.6200a | Acute neurotoxicity screen | Conditionally required | Rat | Single dose to young adults with assessments at predosing, optimum time of effect and at days 7 and 14 | FOB and Motor Activity at pretest, time to peak effect and days 7 and 14 | In situ perfusion with fixative. Paraffin embedding acceptable for CNS but plastic embedding required for peripheral. GFAP immunohistochemistry, Bodian's stain and Bielschowsky's silver methods recommended in addition to standard stains |
| 870.6200b | Subchronic neurotoxicity screen | Rat | Daily dosing with live assessments at predosing, weeks 4, 8 and 13 but histopathology at week 13 only | FOB and Motor activity at pretest, 4th, 8th and 13th weeks | ||
| 870.6300 | Developmental neurotoxicity | Rat | Gestation and lactational exposure. Optional direct pup gavage exposure. Maternal assessments. Pup assessments before weaning and at day ∼21 and day ∼60 | FOB, motor activity. Learning and memory. Acoustic startle response. Brain weight and morphometric | ||
| 870-6500 | Schedule-controlled operant behavior | Rarely conducted or required. Recommended for chemicals showing neurotoxicity in other studies that would be further characterized by this special test. Test can be combined with other guideline studies | Rat | Open | Special operant behavior | Not specified |
| 870.6850 | Peripheral nerve function | Rat | Peripheral nerve conduction velocity and amplitude | Not specified | ||
| 870.6855 | Neurophysiology: sensory evoked potentials | Pigmented rat strain | Implantation of electrodes in brain followed by visual, auditory or somatosensory stimuli evaluated | Not specified | ||
Most commonly used species.
For organophosphates and carbamates, plasma cholinesterase and RBC and brain acetylcholinesterase are periodically assessed.
*The guidelines recommend rats to be tested but other species can be tested under special circumstances.
Copies available at http://www.epa.gov/pesticides (see under Science and Policy-Test Guidelines).