Biomedical subjects

I Halvorson

Publications and source records attributed to I Halvorson.

12 recordsLinked to original sources

PubMed1994

Activation of shivering and non-shivering thermogenesis by electrical stimulation of the lateral and medial preoptic areas.

Experiments were conducted to determine if the area of stimulation within the preoptic area and/or the magnitude of the electrical stimulus applied to the preoptic region would selectively alter the evoked thermogenic responses of normothermic and hypothermic rats. Urethane anesthetized male, Long-Evans rats kept at 37 degrees C, and later cooled to 34 degrees C, were given unilateral electrical stimulation (0.5 ms pulses of 200 microA at 50 Hz for 30 and 300 s) into either the medial preoptic area (MPO) or the lateral preoptic area (LPO). Temperature changes of intrascapular brown adipose tissue, TIBATs; of gastrocnemius muscle, Tms, tail, Tts and colonic Tcs via thermistor probes were recorded before and after stimulation along with differential, multi-unit EMG activity of the gastrocnemius muscle via implanted stainless steel electrodes. The group kept at 37 degrees C and given MPO electrical stimulations evoked graded increases in TIBATs above core dependent on the duration of the electrical stimulus but shivering did not occur and Tms did not rise. When kept at 34 degrees C the MPO-stimulated group showed greater increases in TIBATs than respective responses seen when the same stimuli were applied at 37 degrees C. The group maintained at 37 degrees C and given LPO stimuli over 300 s increased Tms as shivering occurred, yet no change in TIBATs were observed. When cooled to 34 degrees C LPO stimulation (30 or 300 s duration) showed greater shivering activity. Interesting, LPO stimulation of animals maintained at 34 degrees C also caused TIBAT to increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗

PubMed1994

Electrical stimulation of the posterior and ventromedial hypothalamic nuclei causes specific activation of shivering and nonshivering thermogenesis.

Experiments were designed to determine in the same animal whether electrical stimulation of the posterior hypothalamus and ventromedial hypothalamic nucleus could specifically evoke shivering and nonshivering (brown adipose tissue) thermogenesis, respectively, in anesthetized, normothermic rats. Urethane-anesthetized, male Long-Evans rats, kept at 37 degrees C, had colonic (Tc), gastrocnemius muscle (Tm), intrascapular brown adipose tissue (TIBAT), and tail (Tt) temperatures measured via thermistor probes, and electromyogram activity (differential multiunit activity from bipolar recording electrodes within gastrocnemius muscle) recorded, before and after unilateral electrical stimulation (monophasic 0.5-ms pulses of 200 microA at 50 Hz for 30 s) of the posterior hypothalamus and ventromedial hypothalamic nucleus (via stereotaxically implanted concentric stimulating electrodes). Each rat showed shivering (increased electromyogram activity) following posterior hypothalamic stimulation, which caused an immediate rise in Tm values with no change in TIBAT or Tt values. Electrical stimulation of the ventromedial hypothalamic nucleus of the same animals elicited no shivering activity, but significant increases in TIBAT values occurred with no change in Tm or Tt values. Results confirm that stimulation of the posterior and ventromedial hypothalamic nuclei in rodents specifically activates shivering and nonshivering (brown adipose tissue) effector mechanisms, respectively, to raise core temperature.

Adipose Tissue, Brown↗

PubMed1994

Brown adipose tissue thermogenesis evoked by medial preoptic stimulation is mediated via the ventromedial hypothalamic nucleus.

Experiments were designed to determine if a functional ventromedial hypothalamic nucleus was required for the activation of brown adipose tissue thermogenesis evoked by medial preoptic stimulation. Male, urethane-anesthetized Long--Evans rats, maintained at 37 degrees C, had temperatures (thermistor probes for gastrocnemius, Tm; intrascapular brown adipose tissue, TIBAT; colonic, Tc; and tail, Tt), gastrocnemius electromyogram activity (via stainless steel recording electrodes), and systemic blood pressure and heart rate (via a femoral arterial catheter) measured before and after a series of unilateral medial preoptic electrical stimulations (monophasic 0.5-ms pulses of 300 microA at 50 Hz for 30 s). Measurements were made (i) after an initial control medial preoptic electrical stimulation, (ii) after medial preoptic stimulation was applied 1 min following an intracranial injection of 300 nL of sterile saline or buffered 2% Lidocaine into the ipsilateral posterior hypothalamic nucleus or the ipsilateral ventromedial hypothalamic nucleus, and (iii) after recovery medial preoptic stimulation 45 min after Lidocaine was injected into the ventromedial hypothalamic nucleus. TIBAT and blood pressure rose significantly (p < 0.05) above the corresponding prestimulation control values with all protocols, except when Lidocaine was injected into the ventro-medial hypothalamic nucleus prior to medial preoptic stimulation. Shivering (electromyogram) activity was not evoked following medial preoptic stimulation and Tm and Tt did not significantly change from the corresponding prestimulation values. A recovery medial preoptic stimulation 45 min after Lidocaine treatment of the ventromedial hypothalamic nucleus again evoked significant increases in TIBAT above the core temperature, similar to the rise in TIBAT seen after the first control medial preoptic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗

PubMed1994

Role of mast cell histamine in brown adipose tissue thermogenic response to VMH stimulation.

Electrical stimulation of the ventromedial hypothalamic area in rats caused a significant but transient increase in interscapular brown adipose tissue temperature. This response was markedly reduced by cimetidine, a histamine H2-receptor antagonist, but not by pyrilamine, an H1-receptor antagonist. Histamine is present in substantial amounts within mast cells in brown adipose tissue as injections of compound 48/80, which cause degranulation of connective tissue mast cells, reduced the tissue histamine content by > 85%. In contrast, histamine content in brown adipose tissue was not affected by loss of sympathetic neural input (with 6-hydroxydopamine) or sensory neural input (with capsaicin). Neither cimetidine nor histamine had any effect on basal and norepinephrine-stimulated rates of O2 consumption by isolated brown adipocytes. These results indicate that histamine released from mast cells acting on H2-receptors may play an important but indirect role in the thermogenic response of brown adipose tissue to stimulation of the ventromedial hypothalamic area.

Adipocytes↗

PubMed1993

Intrascapular brown adipose tissue (IBAT) temperature and blood flow responses following ventromedial hypothalamic stimulation to sham and IBAT-denervated rats.

Intrascapular brown adipose tissue temperature (TIBAT) and capillary blood flow along with colonic (Tc) and tail (Tt) temperatures as well as blood pressure and heart rate responses were measured simultaneously in groups of age-matched, anesthetised, sham control and IBAT-denervated Long-Evans rats following VMH electrical stimulation. Unilateral VMH electrical stimulation (0.5 ms pulses of 100 microA at 50 Hz for 30 s) evoked rises in TIBAT (above core) and IBAT blood flow in the Long-Evans sham control group, along with increases in blood pressure and heart rate. Rises in IBAT temperature and capillary blood flow were absent in the surgical denervated group following VMH electrical stimulation whereas the evoked pressor and tachycardic responses were left intact and were similar to those responses seen in the sham control group. The results indicate that acute bilateral sectioning of the IBAT intercostal nerves blocks the IBAT temperature and capillary blood flow increases evoked by VMH electrical stimulation.

Adipose Tissue, Brown↗

PubMed1993

Posterior hypothalamic stimulation of anesthetized normothermic and hypothermic rats evokes shivering thermogenesis.

Normothermic (37 degrees C), anesthetized Long Evans rats given unilateral electrical stimulation (0.5 ms monophasic pulses of 100-300 microA at 50 Hz for 30 s) of the posterior hypothalamus (PH) had graded, sustained increases in EMG electrical activity of the gastrocnemius muscle (i.e. shivering). In a current-related manner, gastrocnemius muscle temperatures (Tm) immediately increased following PH stimulation, surface temperatures (Tt) did not change and colonic (core, Tc) temperatures initially fell, then subsequently rose after the applied stimulus. A biphasic pressor response occurred after PH electrical stimulation associated with tachycardia. PH electrical stimulation (0.5 ms pulses at 50 Hz for 30 s of only 40 microA) induced shivering in anaesthetized, hypothermic Long Evans rats undergoing acute cold exposure. When these same hypothermic rats were cooled further to cause shivering, PH electrical stimulation (0.5 ms pulses at 50 Hz for 30 s of only 40 microA) induced further increases in the shivering response (increases EMG area of gastrocnemius muscle) from the shivering response before PH stimulation. Results indicate that electrical stimulation of the PH can evoke shivering in anesthetized normothermic rats. Stimulation of the PH with lower current intensity can induce or increase shivering of hypothermic rats previously exposed to the cold.

Anesthesia↗

PubMed1992

Brown adipose tissue temperature responses following electrical stimulation of ventromedial hypothalamic and lateral preoptic areas or after norepinephrine infusion to Long Evans or Sprague-Dawley rats.

Thermoregulatory (brown adipose tissue temperature) experiments were conducted in age-matched anesthetized, male Sprague-Dawley and Long Evans rats kept at 37 degrees C given unilateral electrical stimulation of the ventromedial hypothalamic nucleus or the lateral preoptic area or after intravenous infusion of norepinephrine HCl (50 micrograms/kg total dose). Unilateral electrical stimulation (0.5 ms pulses of 250 microA at 50 Hz for 30 s) of the ventromedial nucleus or lateral preoptic area caused significant rises (greater than 0.6 degrees C) of intrascapular brown adipose tissue temperature in the Long Evans group only. Norepinephrine infusion (0.1 ml/min for 10 min), or intravenous bolus injection of propranolol HCl (2.5 mg/kg) caused significant yet similar increases (greater than 1.0 degrees C) and decreases (greater than -0.3 degrees C), respectively, of intrascapular brown adipose tissue temperature from pre-administration control temperatures in both Long Evans and Sprague-Dawley groups. The results demonstrate that intrascapular brown adipose tissue sensitivity towards exogenous norepinephrine or propranolol administration is similar between Sprague-Dawley and Long Evans rats acclimated to 21 degrees C as determined by increases in temperature in the intrascapular brown adipose tissue pad. However, intrascapular brown adipose tissue thermogenesis of 21 degrees C-acclimated Long Evans rats is also activated after CNS electrical stimulation of the ventromedial nucleus or lateral preoptic area, an activation not seen in Sprague-Dawley rats suggestive that the latter group has some inhibition of neural pathways that activate brown adipose tissue thermogenesis.

Adipose Tissue, Brown↗

PubMed1992

Differences in brown adipose tissue thermogenic responses between Long-Evans and Sprague-Dawley rats.

Temperature experiments of 4- and 21 degrees C-acclimated conscious and anesthetized Sprague-Dawley (SD) and Long-Evans (LE) rats revealed that the LE groups or SD rats acclimated to 4 degrees C had significant increases in intracapsular brown adipose tissue (IBAT) temperature above core after ventromedial hypothalamic nucleus (VMH) electrical stimulation or after norepinephrine (NE) infusion (50 micrograms/kg total dose), whereas IBAT temperatures of SD rats (acclimated to 21 degrees C) rose only after intravenous NE. Another study of 21- or 4 degrees C-acclimated SD rats revealed that only the 4 degrees C-acclimated group showed graded increases in IBAT temperature after VMH electrical stimulation as current amplitude or total current duration (not pulse frequency) of the electrical stimulus was increased. In vitro analysis of isolated IBAT tissues of age-matched anesthetized LE or SD rats acclimated to 21 degrees C showed that many indicators of thermogenic capacity including mitochondrial uncoupling protein were significantly lower in the SD group. The results demonstrate that lean male SD rats acclimated to 21 degrees C have suppressed IBAT temperature responses to VMH electrical stimulation compared with lean LE rats due to a reduced thermogenic capacity of that tissue.

Acclimatization↗

PubMed1990

Brown adipose tissue thermogenesis is activated by electrical and chemical (L-glutamate) stimulation of the ventromedial hypothalamic nucleus in cold-acclimated rats.

Experiments were conducted to determine if both electrical and chemical stimulation of the ventromedial hypothalamic nucleus (VMH) could activate brown adipose tissue (BAT) thermogenesis. Age-matched, room-acclimated (21 degrees C) and cold-acclimated (4 degrees C for 3 weeks prior to testing) male Sprague-Dawley rats were given unilateral electrical or chemical stimulation to the VMH by way of a 'chemotrode apparatus'. The devised 'chemotrode' allowed both electrical stimulation (insulated piano wire stimulating electrode) and chemical stimulation (23 gauge stainless steel intracranial cannula of equal length) to be performed at the same VMH site using a common 19 gauge stainless steel outer guide tube. The first unilateral VMH electrical stimulation (0.5 ms pulse, 50 Hz and 120 microA for 30 s) caused no significant rise in interscapular brown adipose tissue temperature (TIBAT) colonic (Tc) or tail surface temperatures (Tt), compared to respective prestimulation control values in rats acclimated to 21 degrees C. In the 4 degrees C-acclimated group the first VMH electrical stimulation caused a significant rise in IBAT temperature. L-Glutamate administration to the same VMH site (60 nmol in 600 nl volume) also caused a significant increase in IBAT temperature in the 4 degrees C but not the 21 degrees C-acclimated rats. The rise in IBAT temperature following the L-glutamate injection to the 4 degrees C-acclimated group was similar to that found following the first electrical stimulation to this group. Interestingly, a second unilateral electrical stimulation of the VMH to 4 degrees C-acclimated rats could not evoke a similar increase in IBAT temperature suggesting that overall L-glutamate was acting in vivo as an excitotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1990

Brown adipose tissue thermogenic responses of rats induced by central stimulation: effect of age and cold acclimation.

1. Urethane-anaesthetized, age-matched cold-(4 degrees C) and room (21 degrees C)-acclimated groups of Sprague-Dawley rats were given repeated (three) ventromedial hypothalamic electrical stimulations. Interscapular brown adipose tissue (IBAT), colonic, surface tail temperatures and blood pressure were monitored before and after each electrical stimulation. Propranolol HCl (2.5 mg kg-1 i.v.) was given 10 min prior to the last (third) ventromedial hypothalamic stimulation. 2. Repeated electrical stimulation of the ventromedial hypothalamic (VMH) nucleus to either small or large rats (kept at 21 degrees C) caused no significant change in interscapular brown fat, colonic or surface temperatures compared to respective pre-stimulation control values whereas mean arterial pressure was slightly but significantly increased during the 30 s stimulation period. 3. Electrical stimulation of the ventromedial hypothalamic nucleus of small or large rats, kept at 4 degrees C for 3 weeks prior to testing, caused significant (greater than 0.25 and greater than 0.40 degrees C, respectively) rises in interscapular BAT temperature from respective prestimulation control values. Colonic temperatures increased following ventromedial hypothalamic electrical stimulation only in the small, 4 degrees C-acclimated group whereas surface tail temperatures did not significantly change after stimulation of either cold-exposed group. Mean arterial pressures were significantly increased during ventromedial hypothalamic electrical stimulation in both 4 degrees C-acclimated groups, compared to pre-stimulation control levels and, in addition, were above those of age-matched rats kept at 21 degrees C. Intravenous propranolol, which decreased interscapular brown fat and colonic temperatures in all groups, blocked the rise in interscapular brown fat and colonic temperatures of the 4 degrees C-acclimated rats following the last electrical stimulation of the ventromedial hypothalamic nucleus. 4. In vitro biochemical analysis of the interscapular brown fat pads of another four groups of age-matched, small and large 21 and 4 degrees C-acclimated rats revealed that the thermogenic capacity of the 4 degrees C-acclimated groups was, in all cases, significantly increased from age-matched groups previously kept at 21 degrees C, as shown by significant increases in brown adipose tissue mass, BAT DNA and protein content, BAT mitochondrial protein and BAT mitochondrial GDP binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗

PubMedDate not supplied

Computerized blood pressure and heart rate recording system interfaces standard chart recorder with any micro-computer.

The designed inexpensive blood pressure recording system (BPRS) gives any microcomputer direct on-line blood pressure and heart rate recording capability that will save research time and increase the accuracy of collected data. The data is automatically stored in a file compatible with most graphic and statistical processing software. In vitro testing, over a range of 0-200 mmHg and 0-360 beats per minute showed a 0.999 intraclass correlation. In vivo testing of the BPRS used anaesthetized rats whereby their systolic and diastolic pressures were measured simultaneously with heart rate. The blood pressures and heart rate data, measured by the BPRS demonstrated excellent stability, sensitivity and accuracy when compared to those measured by standard pressure transducers in conjunction with a Grass polygraph and a sphygmomanometer.

Animals↗

PubMedDate not supplied

Computer interface and software analysis for multi-channel, on-line temperature recording to any micro-computer.

A simple, inexpensive computer interface designed for in vitro or in vivo researchers with limited electronic experience allows direct on-line multi-channel temperature recording from thermistor probes to any micro-computer. The designed system saves time and increases the accuracy of collected data that are ready for storage in files compatible with graphic and statistical software. In vitro testing of the designed interface, over a range of 25-45 degrees C, showed a 0.999 intraclass correlation to reference water bath temperatures. In vivo testing using anesthetized rats involved simultaneous measurements of: (1) a thermogenic tissue, interscapular brown adipose temperature (IBAT), (2) core (colonic) temperature, and (3) surface (tail) temperature, a heat loss tissue. The temperatures measured by the designed computer-interface demonstrate excellent stability, sensitivity and accuracy when compared to respective temperatures measured by a YSI telethermometer.

Animals↗