Mesodiencephalic and other target regions of ascending spinal projections in the turtle, Pseudemys scripta elegans

Ascending spinal projections were investigated in turtle Pseudemys scripta elegans following injections of radioactive amino acids into the spinal cord at various levels. Experiments using S35-methionine were most successful in demonstrating various mesodiencephalic target areas. Ascending projections from lumbar and cervical segments terminated predominantly in caudal and lateral reticular fields including the perihypoglossal complex. These spinal regions also projected for a lesser extent to rostrolateral and caudomedial reticular fields and to the nucleus (n.) raphe inferior. Afferents terminated consistently within the peritoral region, the optic tectal layers, the mesodiencephalic periventricular white matter, and the ovalis complex. Occasional labeling was noted in the diencephalic white matter adjacent to the optic tract, the n. supraopticus, and in the n. commissuralis anterior. Projections to the so-called rostrolateral perirotundal complex following high cervical injections were less prominent following low cervical and lumbar injections. Cervical afferents terminated in a variable manner in the vestibular complex, the torus semicircularis n. centralis, the mesodiencephalic periventricular gray (griseum centrale, n. interstitialis commissuralis posterior and hypothalamic areas), the n. suprapenduncularis, and the n. reuniens.