| dc.contributor.author | Dick, Susan Heather. | en_US |
| dc.date.accessioned | 2014-10-21T12:33:59Z | |
| dc.date.available | 1999 | |
| dc.date.issued | 1999 | en_US |
| dc.identifier.other | AAINQ49254 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55633 | |
| dc.description | The dorsal column medial lemnsicus (DC-ML) system is a critical pathway for discriminative aspects of light touch. The dorsal column nuclei (DCN) receive sensory input via direct and indirect pathways. The indirect pathway is characterized by a relay in the spinal cord dorsal horn and is referred to as the post-synaptic dorsal column (PSDC) system. To date, descriptions of PSDC neuronal properties have been limited to the rat and cat. The raccoon is an excellent alternative model in which to study the PSDC system because of the highly differentiated somatosensory system and the presence of large glabrous skin areas on the forepaw digits and palm. | en_US |
| dc.description | In this study, single-unit extracellular recordings were made from 102 antidromically identified PSDC neurons and 51 cuneate neurons in response to receptive field (RF) stimulation and during spontaneous discharge. The PSDC neurons studied had RFs on glabrous skin of forepaw digits and/or palm. The RFs were discrete and well defined (9.4 mm2) but were significantly larger than those observed for cuneate neurons in the same animals (6.7 mm 2). There was no difference in the latency of response of PSDC neurons (8.2 ms) vs. cuneate neurons (8.7 ms) in response to electrical stimulation of the RF (i.e., on-focus digit). Similarly, there was no difference between PSDC (9.9 ms) and cuneate (9.9 ms) neurons with respect the latency of response to off-focus stimulation. | en_US |
| dc.description | Little is known about the contribution of the PSDC pathway to the DC-ML system in the processing of mechanosensory information. Using cross-correlation and frequency response analyses, a functional interaction between PSDC and cuneate neurons was identified that occurred only during spontaneous discharge. In 26 of the 51 neuron pairs examined, PSDC neuron activity appeared to be correlated with that of neurons in the cuneate nucleus. When the interaction between PSDC and cuneate neuron pairs was significant, most had overlapping RFs (19/26) and few did not (only 7/26). The mean coherence between PSDC input and cuneate output signals of the spinocuneate connection was 0.3, indicating partial linearity in the PSDC to cuneate interaction. One interpretation of these results is that the PSDC system exerts a somatotopically organized tonic facilitation of cuneate neuron activity, perhaps to control cuneate mechanosensory neuron RF size and excitability. | en_US |
| dc.description | It is known that reorganization of the cuneate nucleus occurs following permanent deafferentation in raccoon. The mechanisms responsible for these changes are unknown but could involve the unmasking of ineffective input to PSDC neurons from an adjacent digit. In this way, deafferented cuneate neurons could become responsive to input from an adjacent digit via a PSDC to cuneate connection. To test this hypothesis, lidocaine was injected into the digit containing the PSDC neuron RF and the response of these cells to stimulation of the adjacent digit was monitored before and during temporary deafferentation. The results indicated that PSDC neurons become even less responsive to stimulation of the adjacent digit during deafferentation, indicating that immediate unmasking of connections does not occur. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1999. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Neuroscience. | en_US |
| dc.title | Functional properties of post-synaptic dorsal column neurons in raccoon. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
