The ventromedial hypothalamic nucleus (VMH) is an important central effector site involved in activating brown adipose tissue (BAT) or non-shivering thermogenesis. VMH neurons have previously been shown to be thermally responsive to changes in local temperature of the preoptic area/anterior hypothalamus (PO/AH). However, the thermoresponsiveness of VMH neurons of room temperature acclimatized and cold acclimatized rats to peripheral thermal stimulation has not been tested. In this thesis, a series of studies was designed to determine the thermoresponsiveness of VMH neurons to peripheral (scrotal) thermal stimulation of rats. Extracelluiar VMH neuronal activity was recorded from urethane anaesthetized male Sprague-Dawley rats, which were acclimatized either to room temperature (21°C for 4 weeks) or to cold (4°C for 4 weeks) prior to testing, during scrotal cooling and heating with glass-micropipettes filled with 0.5 M sodium acetate containing 2% pontamine sky blue. The rats' colonic temperatures were kept at normothermia (37°C), or hypothermia (33-35°C) during scrotal thermal stimulation. In the room temperature acclimatized rats, VMH neurons were temperature responsive to scrotal heating and cooling and were classified as warm responsive (WRN), cold responsive (CRN) and temperature non-responsive neurons (TNRN), based on their thermal coefficients. The ratio of VMH WRNs and CRNs was similar to that of thermoresponsive neurons observed in other brain regions (eg, the PO/AH and thalamus). VMH WRNs and CRNs were further classified as biphasic or monophasic in nature according to their thermal responses to scrotal heating and cooling. VMH neurons sustained their thermoresponsiveness to repeated trials of scrotal thermal stimulation with colonic temperatures maintained at 37°C or when colonic temperatures were acutely lowered from 37°C to 35°C and 33°C. In addition, scrotal thermal signals specifically altered neuronal activity of VMH thermoresponsive neurons, as changes in EEG activity did not occur with changes in VMH neuronal activity. Scrotal thermal inputs were functionally shown to be transmitted via the medial preoptic nucleus (MPO) prior to reaching the VMH nucleus because thermoresponsive VMH neuronal activity was blocked with the pretreatment of lidocaine into the MPO. Scrotal heating or cooling to 21°C-acclimatized rats did not increase IBAT temperatures, inferring that scrotal cooling had not evoked IBAT thermogenesis in this group. In cold acclimatized (CA) rats, prolonged (over 2 hours) and transient localized scrotal cooling caused IBAT temperatures to increase, inferring that scrotal cooling activated BAT thermogenesis. Mean basal firing rates of all recorded VMH neurons of CA-groups significantly increased, compared to those of VMH neurons observed in room temperature acclimatized (RA) groups. More VMH CRNs than WRNs were recorded in the CA-group and the thermoresponsiveness (ie, thermal coefficient) of VMH CRNs significantly increased during localized scrotal cooling in the cold acclimatized group, compared to thermal coefficients of VMH CRNs of the RA-groups. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-10212004-000223 |
| Date | 01 January 1996 |
| Creators | Li, Qiang |
| Contributors | Thornhill, James |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-10212004-000223 |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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