Laterally Versus Medially Projecting Spinothalamic Neurons and their Axon Collaterals to the Periaqueductal Gray and Medullary Reticular Formation in the Rat
Abstract
Fluorescent, retrograde tracing studies were undertaken to compare laterally (L-STT) versus medially (MSTT) projecting spinothalamic tract neurons in terms of their axon collaterals to the periaqueductal gray (PAG) or medullary reticular formation (MRF). The tracers used for these double-label experiments were fast blue or fluorogold in combination with rhodamine-labeled latex microspheres. Under general anesthesia, the tracers were injected into the lateral thalamus and MRF (N=6), lateral thalamus and PAG (N=S), medial thalamus and MRF (N=6), or medial thalamus and PAG (N=S). After 7 days, the animals were deeply anesthetized and perfused. The brains and spinal cords were removed and processed according to standard protocols. Locations of single- and double-labeled STT neurons were plotted for the spinal enlargements, mid-thoracic and upper cervical segments. In all segments examined, single- and double-labeled L-STT and M-STT neurons were commonly observed in contralateral laminae V-VIII and, at upper cervical levels, in ipsilateral laminae VII-VIII. The percentages of STT cells which were double-labeled (10-40%) in these areas were similar across the experimental conditions, but were generally highest in the upper cervical and lowest in mid-thoracic segments. The lateral spinal nucleus contained double-labeled STT neurons in all four experimental groups. More 1-STT than M-STT neurons were observed in lamina I in the cervical enlargement some of these were double-labeled from the PAG, but not from the MRF. In the lumbar enlargement, many L-STT neurons, none of which were double-labeled, were seen in the ventromedial dorsal horn. Such populations of exclusively single-labeled L-STT neurons were also found at upper cervical levels in the internal basilar and lateral cervical nuclei. These data suggest that many L-STT and M-STT neurons issue axon collaterals to the PAG or MRF.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 30, 1987
- Accession Number
- ADA634955
Entities
People
- Constance M. Pechura
Organizations
- Uniformed Services University of the Health Sciences