Administration of muscimol into the posterior hypothalamus reduces hyperthermia induced by hippocampal neostigmine injection

Thyrotropin-releasing hormone induced thermogenesis in Syrian hamsters: Site of action and receptor subtype

Early work in our laboratory has revealed the important role played by thyrotropin-releasing hormone (TRH) in the arousal from hibernation in Syrian hamsters. In the present study, we investigated the thermogenic mechanism of TRH in Syrian hamsters. Six to 10 female Syrian hamsters were used in the respective experiments. Intracerebroventricular (icv) injection of TRH elevated the intrascapular brown adipose tissue (IBAT) temperature (T(IBAT)) and rectal temperature (T rec) in Syrian hamsters. Thermogenic response of icv TRH was suppressed by bilateral denervation of the sympathetic nerve. Icv injection of TRH increased the norepinephrin (NE) turnover rate in IBAT without affecting the total serum triiodothyronine (T3) level. Moreover, TRH microinjections into the dorsomedial hypothalamus (DMH), preoptic area (PO), anterior hypothalamus (AH) and ventromedial hypothalamus (VMH) induced T(IBAT) and T(rec) increases. However, neither T(IBAT) nor T rec was affected by similar TRH administrations into the lateral hypothalamus and posterior hypothalamus. Interestingly, although TRH-induced hyperthermia was suppressed by pretreatment of anti-TRH-R1 antibodies, no changes were induced by anti-TRH-R2 antibodies. These results suggest that the sites of action of TRH associated with thermogenesis are probably localized in the DMH, PO, AH and VMH. In addition, TRH-induced thermogenesis is probably elicited by facilitation of the sympathetic nerve system via the central TRH-R1 irrelevant of T3.

Evidence that GABAergic neurons in the spinal trigeminal nucleus are involved in the transmission of inflammatory pain in the rat: a microdialysis and pharmacological study

The aim of this experiment was to investigate the role of the gamma-aminobutyric acid (GABA)-ergic transmission in the nociception within the spinal trigeminal nucleus. The formalin test was used as an animal model of inflammatory pain. Two groups of six rats were used. The behavioural response to the labial injection of formaldehyde (50 microl of a 5% solution) (group 1) or saline (group 2) was evaluated by recording the time spent in facial grooming during a period of 8 min (one period before and seven consecutive periods after the injection). The extracellular concentration of GABA in the trigeminal caudalis nucleus was evaluated, during the formalin test, on samples of 30 microl each (one sample before and three samples after the labial injection) obtained by microdialysis and analysed by HPLC with electrochemical detection of the o-phtalaldeyde pre-column derivate. Subsequently, three more groups of six rats each were injected with saline, muscimol (GABAa receptor agonist), or bicuculline (GABAa receptor antagonist) in the trigeminal caudalis nucleus, before performing the formalin test. The injection of formaldehyde induced a biphasic behavioural response and an increase of the GABA levels at 15-45 min. The injection of bicuculline, but not muscimol or saline, strongly decreased the behavioural response of the formalin test. These findings suggest that GABAergic neurons in the trigeminal caudalis nucleus are involved in the transmission of nociceptive information.

An aversive diet as thiamine-free food blocks food-induced release of excitatory amino acids in the accumbens

AIMS

As the nucleus accumbens shell plays an important role in the control of eating behaviour, the aim of this study was to evaluate the changes in: (a) the level of aspartic and glutamic acids in the accumbens shell of conditioned rats after the presentation of an aversive diet containing thiamine-free food; (b) the temperature of interscapular brown adipose tissue, effector of thermogenesis related to food intake.

METHODS

The concentration of aspartic and glutamic acids in the accumbens shell, and brown adipose tissue temperature were monitored in conditioned male Sprague-Dawley rats before and after the presentation of thiamine-free food or standard laboratory food. The aspartic and glutamic acids were collected using a microdialysis probe and quantified by HPLC. Food intake was also measured.

RESULTS

The results indicated that an intake of standard laboratory food induced an increase in the level of aspartic and glutamic acids, and an elevation in temperature of brown adipose tissue; whereas an intake of thiamine-free food blocks these increases in the conditioned animals.

CONCLUSION

The thiamine-free diet modifies the release of excitatory amino acids in the nucleus accumbens of conditioned animals. This diet also affects thermogenesis.