The mammalian ventrobasal thalamus (VB) is the location of the final processing of somatosensory information before it is relayed to the cerebral cortex. Most of our knowledge of the somatosensory thalamus relates to thalamocortical relay (TCR) neurons while relatively little is known about the local circuit neurons (LCNs) which comprise approximately 25% of the VB neuronal population. As the LCNs are known to be GABAergic and constitute a major component of the inhibitory processes in the thalamus these neurons play a central role in thalamic function. Knowledge of the anatomical and physiological organization of the VB is necessary to understand the bases of somatic sensation and particularly the differences between the relay of noxious (pain producing) and non- noxious stimuli. The research proposed here is designed to study the morphology of local circuit neurons (LCNs) in the cat VB complex. The study will use both anatomical and physiological methods to examine the synaptic input to LCNs. In the anatomical studies, LCNs will be identified immunocytochemically by the presence of GABA. The number and distribution of synaptic terminals derived from the dorsal column nuclei (DCN), spinothalamic tract (STM, cerebral cortex and thalamic reticular nucleus (TRN) will be determined using axonal transport (PHA-L) or degeneration methods. A second series of experiments involve the physiological characterization (i.e. receptive field properties) and subsequent intracellular HRP filling of LCNs. The morphology and axonal projections of the filled LCNs will be studied at the LM level. This study will provide information on the synaptic connectivity of LCNs similar to that presently available for TCR neurons. It will be determined in what way the synaptic organization and response properties of LCNs may affect the transfer of somatosensory information through the thalamus. Differences between the organization of pathways associated with noxious and non-noxious sensation will provide insight into the role of the thalamus in pain mechanisms.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS026488-03
Application #
3412362
Study Section
Neurology B Subcommittee 2 (NEUB)
Project Start
1990-09-28
Project End
1994-08-31
Budget Start
1992-09-01
Budget End
1994-08-31
Support Year
3
Fiscal Year
1992
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Type
Schools of Medicine
DUNS #
073133571
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Meng, X W; Ohara, P T; Ralston 3rd, H J (1998) Nitric oxide synthase containing neurons in the ventral lateral geniculate of the rat project to the optic pretectal nuclei. Neurosci Lett 256:89-92
Meng, X W; Ohara, P T; Ralston 3rd, H J (1996) Nitric oxide synthase immunoreactivity distinguishes a sub-population of GABA-immunoreactive neurons in the ventrobasal complex of the cat. Brain Res 728:111-5
Ohara, P T; Havton, L A (1996) Dendritic arbors of neurons from different regions of the rat thalamic reticular nucleus share a similar orientation. Brain Res 731:236-40
Ohara, P T; Ralston 3rd, H J; Havton, L A (1995) Architecture of individual dendrites from intracellularly labeled thalamocortical projection neurons in the ventral posterolateral and ventral posteromedial nuclei of cat. J Comp Neurol 358:563-72
Havton, L A; Ohara, P T (1994) Cell body and dendritic tree size of intracellularly labeled thalamocortical projection neurons in the ventrobasal complex of cat. Brain Res 651:76-84
Ohara, P T; Havton, L A (1994) Preserved features of thalamocortical projection neuron dendritic architecture in the somatosensory thalamus of the rat, cat and macaque. Brain Res 648:259-64
Williamson, A M; Ohara, P T; Ralston, D D et al. (1994) Analysis of gamma-aminobutyric acidergic synaptic contacts in the thalamic reticular nucleus of the monkey. J Comp Neurol 349:182-92
Havton, L A; Ohara, P T (1994) Dendritic orientation of thalamocortical projection neurons in the ventrobasal complex of macaques. Brain Res 638:126-32
Ohara, P T; Lieberman, A R (1993) Some aspects of the synaptic circuitry underlying inhibition in the ventrobasal thalamus. J Neurocytol 22:815-25
Havton, L A; Ohara, P T (1993) Quantitative analyses of intracellularly characterized and labeled thalamocortical projection neurons in the ventrobasal complex of primates. J Comp Neurol 336:135-50

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