Details

Autor(en) / Beteiligte

• Woods, A.J

Titel

Thermal and vasomotor responses to hypothalamic stimulation

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1991

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Experiments were undertaken to investigate interscapular brown adipose tissue (IBAT) temperature responses to hypothalamic electrical stimulation. It was found that low frequency electrical stimulation of the ventromedial hypothalamus (VMH; 15Hz, 7 A, 0.5ms) produced a biphasic temperature response in IBAT. The first phase (Phase 1) was a rapid decrease, which was maintained as long as the stimulus was applied. The second phase (Phase 2) was a marked and rapid increase in temperature that occurred immediately after the stimulus was removed; both phases require an intact sympathetic nerve supply to IBAT. This rise is known, and was confirmed to be a -adrenergic mediated response. The decrease in temperature (Phase 1) was previously thought to be an -adrenergic mediated response, but this was not confirmed, and evidence was obtained to suggest an involvement of a -adrenergic mediated mechanism. It was found that Phase 1 could be abolished by electrolytic lesions of the lateral hypothalamus (LH), demonstrating a reciprocal interplay between the VMH and the LH. It was also found that Phase 1 could be mimicked by central (icv) injection of dopamine, and blocked by the dopamine antagonists, haloperidol and pimozide. Phase 1 could also be mimicked by peripheral injection of substance P, and blocked by a substance P antagonist. Thiorphan, an inhibitor of substance P degradation, potentiated the decrease in temperature. These results suggest that dopamine may be a central mediator, and substance P (possibly in conjunction with a -adrenergic mechanism) a peripheral mediator of the Phase 1 response. Blood flow measurements using both 14C-DDT and dual-labelled microspheres showed that during Phase 1 there was a decrease in capillary blood flow, whilst there was a large increase in capillary flow during Phase 2. In addition, substance P was shown to cause a large reduction in capillary flow to IBAT but not to perirenal or periaortic BAT. Measurements of oxygen tension in the venous blood draining interscapular BAT during both phases were also carried out.