A quantitative study of brainstem projections from lamina I neurons in the cervical and lumbar enlargement of the rat.
Lamina I of the rat spinal cord contains neurons that project to various brain areas including thalamus, periaqueductal grey matter (PAG), lateral parabrachial area (LPb), caudal ventrolateral medulla and a region in dorsal medulla that includes the nucleus tractus solitarius and dorsal reticular nucleus. We have shown that spinothalamic lamina I neurons are infrequent in rat lumbar enlargement, where they constitute approximately 5% of the estimated 400 projection neurons on each side of the L4 segment (Al-Khater and Todd, 2009). They are more numerous in cervical enlargement, but the total number of lamina I projection neurons in this region was not known. Here we have used paired injections of retrograde tracers into the brainstem to estimate the number of lamina I projection cells in the C7 segment. Our results suggest that there are approximately 215 lamina I projection cells per side, and that spinothalamic cells therefore make up approximately 42% of this population. The proportion of lamina I projection neurons labelled from PAG is higher in cervical than lumbar enlargement, while the proportion labelled from dorsal medulla is similar in the two regions. We also found that lamina I cells in L4 that project to the dorsal medulla are included in the population retrogradely labelled from LPb, thus confirming the estimate that there are around 400 lamina I projection cells in this segment.
Neuroscience and Molecular Pharmacology, Faculty of Biomedical and Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, UK.
Erika
E
Polgár
Lorna L
LL
Wright
Andrew J
AJ
Todd
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D001933:Brain Stem / Q000502:physiology*; D002452:Cell Count; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D008297:Male; D018613:Microscopy, Confocal; D056325:Neuronal Tract-Tracers; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000502:physiology*; D013133:Spinothalamic Tracts / Q000502:physiology; D013788:Thalamus / Q000502:physiology*
D005456:Fluorescent Dyes; D056325:Neuronal Tract-Tracers