Rhesus monkeys with late-onset hydrocephalus differ from non-impaired animals during neonatal neurobehavioral assessments: Six-year retrospective analysis

Background and Purpose: A recent case study indicated that a hydrocephalic rhesus monkey had abnormal response patterns in a standardized neonatal pri mate assessment, We conducted a retrospective study to determine whether th is assessment could also differentiate neonatal rhesus monkeys that appeare d normal but developed signs of hydrocephalus later in life from neonates w ith normal development and no evidence of hydrocephalus. Methods: One-hundred eighty-two rhesus monkeys were assessed on postnatal d ays 7, 14, 21, and 30, As neonates, clinical signs of hydrocephalus or othe r illnesses were not evident in any animal. Six monkeys developed signs of hydrocephalus between 5 months and 5 years of age, and each received confir med diagnoses of hydrocephalus at necropsy. Results: Compared with colony norms, the monkeys that developed hydrocephal us had diminished orientation abilities, more muscle tension, less behavior al evidence of distress, and more pronounced responses to some reflex-evoki ng stimuli, and difficulty in self-righting (day 7 only). Discriminant func tion analysis comparing the hydrocephalic animals with a matched control gr oup provided a high probability of correct group assignment at days 7, 14, and 21. Conclusions: Some as yet undetermined factor may predispose some monkeys to develop hydrocephalus, which may also be reflected in different scores on neurodevelopmental test items during early infancy.