title: Neurotransmitter phenotypes of descending systems in the rat lumbar spinal cord.
abstract: Descending systems from the brain exert a major influence over sensory and motor processes within the spinal cord. Although it is known that many descending systems have an excitatory effect on spinal neurons, there are still gaps in our knowledge regarding the transmitter phenotypes used by them. In this study we investigated transmitter phenotypes of axons in the corticospinal tract (CST); the rubrospinal tract (RST); the lateral component of the vestibulospinal tract (VST); and the reticulospinal tract (ReST). They were labelled anterogradely by stereotaxic injection of the b subunit of cholera toxin (CTb) into the motor cortex, red nucleus, lateral vestibular nucleus and medial longitudinal fascicle (MLF) to label CST, RST, VST and ReST axons respectively. Neurotransmitter content of labelled axons was investigated in lumbar segments by using immunoflurescence; antibodies against vesicular glutamate transporters (VGLUT1 and VGLUT2) were used to identify glutamatergic terminals and the vesicular GABA transporter (VGAT) was used to identify GABA- and glycinergic terminals. The results show that almost all CST (96%) axons contain VGLUT1 whereas almost all RST (97%) and VST (97%) axons contain VGLUT2. Although the majority of ReST axons contain VGLUT2 (59%), a sizable minority contains VGAT (20%) and most of these terminals can be subdivided into those that are GABAergic or those that are glycinergic because only limited evidence for co-localisation was found for the two transmitters. In addition, there is a population of ReST terminals that apparently does not contain markers for the transmitters tested and is not serotoninergic. We can conclude that the CST, RST and VST are 'pure' excitatory systems whereas the ReST consists of a heterogeneous population of excitatory and inhibitory axons. It is anticipated that this information will enable inputs to spinal networks to be defined with greater confidence.
authors.affiliation: Spinal Cord Group, Institute of Neuroscience and Psychology, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
authors.forename: A
authors.initials: A
authors.lastname: Du Beau
authors.forename: S
authors.initials: S
authors.lastname: Shakya Shrestha
authors.forename: B A
authors.initials: BA
authors.lastname: Bannatyne
authors.forename: S M
authors.initials: SM
authors.lastname: Jalicy
authors.forename: S
authors.initials: S
authors.lastname: Linnen
authors.forename: D J
authors.initials: DJ
authors.lastname: Maxwell
mesh_terms: D000818:Animals; D002772:Cholera Toxin / Q000378:metabolism; D004525:Efferent Pathways / Q000502:physiology*; D050485:GABA Plasma Membrane Transport Proteins / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000378:metabolism; D008161:Lumbosacral Region; D008297:Male; D018377:Neurotransmitter Agents / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism; D013116:Spinal Cord; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism; D050599:Vesicular Glutamate Transport Protein 2 / Q000378:metabolism
chemical_list: D050485:GABA Plasma Membrane Transport Proteins; D018377:Neurotransmitter Agents; C493475:Slc17a6 protein, rat; C493466:Slc17a7 protein, rat; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D012701:Serotonin; D002772:Cholera Toxin; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1