GABA is one of the two main inhibitory neurotransmitters in the central nervous system, CNS (along with glycine, which has a major role in the brainstem and spinal cord). GABA regulates a number of functions in the CNS, and in the spinal cord, it is responsible for presynaptic inhibition of primary afferents and postsynaptic inhibition of neurons. GABA is produced by decarboxylation of L-glutamate by glutamate decarboxylase (GAD). Two GAD isoforms have been identified, GAD65 and GAD67. Antibodies raised against glutaraldehyde conjugates of GABA have been used to investigate the distribution of GABAergic cell bodies, whilst the distribution of GABAergic terminals has been examined with antibodies against GAD. Although GABAergic cell bodies are detected throughout the spinal grey matter, these are concentrated in laminae I-III of the spinal dorsal horn. GAD is present in axon terminals in all laminae of the rat spinal cord, but only a few immunoreactive cell bodies have been detected in the superficial dorsal horn. This differs from the situation in the brain, where many GAD-immunoreactive cell bodies can be found. Studies in the brain suggest that while most (if not all GABAergic neurons) synthesise both GAD isoforms, many have relatively high levels of one or other isoform. It is not known whether this is the case in the spinal cord. Until recently, most studies that have looked at the distribution of GAD have used antibodies that do not differentiate between the two isoforms, and such studies in the spinal cord have been qualitative and no attempt has been made to quantify GAD levels in individual laminae, or examine the co-localisation of GAD isoforms in individual boutons. The recent availability of antibodies that are directed against each isoform separately enables detailed studies to be performed that compare the distribution and co-localisation of the two isoforms, in this study, immunocytochemistry and confocal microscopy were used to examine the distribution and co-localisation of GAD65 and GAD67 in individual axonal boutons in each lamina of the rat spinal grey matter. The main finding of this part of the study was that although most GAD- immunoreactive boutons were labelled with both GAD65 and GAD67 antibodies, some showed similar intensities of both types of immunoreactivity whilst others appeared to have relatively higher levels of one or other of the GAD isoforms. This suggests that GAD-immunoreactive neurons are a heterogeneous population. Also, GAD-immunoreaetivity differed between each lamina of the spinal cord e.g. in the superficial dorsal horn, boutons that had relatively higher levels of either GAD65 or GAD67 were frequently found. In contrast, most boutons in the ventral horn displayed relatively high levels of GAD67, although discrete clusters of boutons that had high levels of GAD65 immunoreactivity were detected in lamina IX.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:433081 |
| Date | January 2006 |
| Creators | Mackie, Margaret |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/9059/ |
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