An abnormal distribution of melatonin receptors in the newborn rat with inherited prenatal hydrocephalus.

Melatonin binding in the brain of hydrocephalic H-Tx rats was examined by autoradiography. At the time of birth, hydrocephalic animals showed an abnormality in the distribution of high-affinity melatonin receptors dorsal to the cerebral aqueduct when compared to controls. Whereas newborn rats of the H-Tx strain that were unaffected by hydrocephalus had melatonin receptors in a tectal midsagittal strip overlying the aqueduct and spanning the anterior half of the tectum, hydrocephalic rats lacked melatonin receptors in the most anterior part of this region. In these animals, the length of the aqueduct over which receptors were missing was compressed and was additionally occluded by dystrophic ependyma. The first signs of ventricular expansion characteristic of hydrocephalus were evident.