Central connections of the pineal organ in the three-spined stickleback, Gasterosteus aculeatus L. (teleostei).

Central connections of the pineal organ of the three-spined stickleback, Gasterosteus aculeatus L., were studied by the use of horseradish peroxidase (HRP) for anterograde tracing. The pineal tract terminates bilaterally in the habenular nuclei, area praetectalis, dorsal and ventral thalamic nuclei, periventricular hypothalamus, and dorsal tegmentum. Furthermore, fibers were traced into the rostral hypothalamus, tuberal nuclei and deep tegmentum. No pinealopetal connections were observed.