Lesions of the iodomelatonin-binding sites of the mediobasal hypothalamus spare the lactotropic, but block the gonadotropic response of male Syrian hamsters to short photoperiod and to melatonin.

Endocrinology ◽  
1995 ◽  
Vol 136 (1) ◽  
pp. 144-153 ◽  
Author(s):  
E S Maywood ◽  
M H Hastings
Keyword(s):  
Binding Sites ◽  
Short Photoperiod ◽  
Mediobasal Hypothalamus ◽  
Syrian Hamsters

GDP binding to hamster brown fat mitochondria is reduced during hibernation

1985 ◽  
Vol 249 (6) ◽  
pp. R689-R693 ◽  
Author(s):  
B. A. Horwitz ◽  
J. S. Hamilton ◽  
K. S. Kott
Keyword(s):  
Binding Sites ◽  
Mitochondrial Protein ◽  
Substantial Reduction ◽  
Brown Fat ◽  
Short Photoperiod ◽  
Syrian Hamsters ◽  
Hydroxyacyl Coa Dehydrogenase ◽  
Brown Fat Mitochondria ◽  
Important Site ◽  
Thermogenic Capacity

Preparation for hibernation is accompanied by increased thermogenic capacity of brown fat (BAT), an important site of thermogenesis during arousal from hibernation. This study examined whether that thermogenic capacity is reduced in hibernation and reactivated during arousal. In one set of experiments, Syrian hamsters were exposed to short photoperiod (10:14 light-dark) and cold (7 degrees C). Those not hibernating at death (n = 10) served as controls for those that were (n = 9). A third group (n = 10) was killed 80–90 min after arousal was initiated by manual perturbation. Mitochondrial GDP binding (nmol/mg mitochondrial protein) was used to estimate thermogenic capacity. In a second experimental series, BAT citrate (si)-synthase and 3-hydroxyacyl-CoA dehydrogenase activities were measured in hibernating and nonhibernating hamsters. Although there were no differences in the maximum activities of these enzymes, GDP binding was markedly lower in the hibernators relative to the nonhibernators (0.214 +/- 0.031 vs. 0.535 +/- 0.039). However, in the partially aroused hamsters, GDP binding had doubled (0.438 +/- 0.04). Thus hibernation is accompanied by a substantial reduction of BAT thermogenic capacity (as manifested by GDP binding), which is reversed during arousal. The rapidity of this reversal indicates that it does not involve the synthesis of new GDP binding sites.

Melatonin increases the ratio of 5-hydroxyindoleacetic acid to serotonin in the hypothalamus and brainstem concurrently with gonadal involution in male Syrian hamsters

1991 ◽  
Vol 69 (4) ◽  
pp. 1004-1009 ◽  
Author(s):  
J. Vriend
Keyword(s):  
Luteinizing Hormone ◽  
Thyroid Hormones ◽  
Serum Levels ◽  
Mediobasal Hypothalamus ◽  
Serotonergic Neurons ◽  
Catecholamine Synthesis ◽  
Syrian Hamsters ◽  
Catecholamine Turnover ◽  
Hydroxyindoleacetic Acid

Gonadal involution, with reduced serum levels of luteinizing hormone and prolactin, was induced in male Syrian hamsters by daily injections of melatonin, given in the evening. Highly significant increases in daytime concentrations of 5-hydroxyindoleacetic acid (5-HIAA) and in the ratio of 5-HIAA to serotonin (5-HT) were noted in extracts of mediobasal hypothalamus of melatonin-treated hamsters. An increase in the 5-HIAA/5-HT ratio, with decreased 5-HT concentrations, was found in brainstem extracts of hamsters treated with melatonin. The increase in the 5-HIAA/5-HT ratio was not prevented by inhibition of catecholamine synthesis with α-methyl-p-tyrosine, which suggests that the melatonin-induced increase in the 5-HIAA/5-HT ratio was not due to changes in catecholamine turnover. These results are consistent with the view that serotonergic neurons terminating in the hypothalamus mediate the melatonin-induced inhibition of luteinizing hormone, prolactin, and thyroid hormones accompanying gonadal involution.

Circadian and Photoperiodic Time Measurement in Male Syrian Hamsters Following Lesions of the Melatonin-Binding Sites of the Paraventricular Thalamus

1992 ◽  
Vol 7 (3) ◽  
pp. 241-254 ◽  
Author(s):  
Francis J. P. Ebling ◽  
Elizabeth S. Maywood ◽  
Trevor Humby ◽  
Michael H. Hastings
Keyword(s):  
Binding Sites ◽  
Time Measurement ◽  
Syrian Hamsters ◽  
Paraventricular Thalamus
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