ABSTRACT
The serotonergic neurons of the dorsal raphe (DR) nucleus in the CNS are involved in fear, anxiety and depression. Depression and anxiety occur quite frequently in postmenopausal women, but estrogen replacement to correct these CNS disorders is at present not favored because estrogen carries with it an increased risk for breast cancer. Serotonin synthesis, release and reuptake in the DR are targets of pharmaceuticals in the treatment of depression. In the present study we have examined by immunohistochemistry, the expression of two nuclear receptors, that is, the estrogen receptors ERα and ERß. We found that ERß but not ERα is strongly expressed in the DR and there is no sex difference and no change with ageing in the number of tryptophan hydroxylase (TPH)-positive neurons in the DR of wild-type (WT) mice. However, in ovariectomized (OVX) WT and in ERß(-/-) mice, there was a marked reduction in the number of TPH-positive normal-looking neurons and a marked increase in TPH-positive spindle-shaped cells. These neuronal changes were prevented in mice 1-3 weeks (but not 10 weeks) after OVX by the selective ERß agonist, LY3201, given as continuous release pellets for 3 days. The ERß agonist had no effects on glucose homeostasis. Thus, the onset of action of the ERß agonist is rapid but there is a limited window in time after estrogen loss when the drug is useful. We conclude that, rather than estradiol, ERß agonists could be useful pharmaceuticals in maintaining functional DR neurons to treat postmenopausal depression.
Subject(s)
Estrogen Receptor beta/metabolism , Gene Expression Regulation/genetics , Raphe Nuclei/cytology , Serotonergic Neurons/physiology , Animals , Area Under Curve , Benzopyrans/pharmacology , Cell Count , Estradiol/pharmacology , Estrogen Receptor alpha/deficiency , Estrogen Receptor beta/agonists , Estrogen Receptor beta/deficiency , Female , Gene Expression Regulation/drug effects , Glucose Tolerance Test , Glucose Transporter Type 4/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Muscle, Skeletal/metabolism , Ovariectomy , Serotonin/metabolism , Sex Characteristics , Time Factors , Tryptophan Hydroxylase/metabolismABSTRACT
The GLUT4 transporter plays a key role in insulin-induced glucose uptake, which is impaired in insulin resistance. The objective of the present study was to investigate the tissue content and the subcellular distribution of GLUT4 protein in 4- to 12-year-old control, obese and insulin-treated diabetic mongrel female dogs (4 animals per group). The parametrial white adipose tissue was sampled and processed to obtain both plasma membrane and microsome subcellular fractions for GLUT4 analysis by Western blotting. There was no significant difference in glycemia and insulinemia between control and obese animals. Diabetic dogs showed hyperglycemia (369.9 +/- 89.9 mg/dl). Compared to control, the plasma membrane GLUT4, reported per g tissue, was reduced by 55% (P < 0.01) in obese dogs, and increased by 30% (P < 0.05) in diabetic dogs, and the microsomal GLUT4 was increased by approximately 45% (P < 0.001) in both obese and diabetic animals. Considering the sum of GLUT4 measured in plasma membrane and microsome as total cellular GLUT4, percent GLUT4 present in plasma membrane was reduced by approximately 65% (P < 0.001) in obese compared to control and diabetic animals. Since insulin stimulates GLUT4 translocation to the plasma membrane, percent GLUT4 in plasma membrane was divided by the insulinemia at the time of tissue removal and was found to be reduced by 75% (P < 0.01) in obese compared to control dogs. We conclude that the insulin-stimulated translocation of GLUT4 to the cell surface is reduced in obese female dogs. This probably contributes to insulin resistance, which plays an important role in glucose homeostasis in dogs.
Subject(s)
Adipocytes/metabolism , Diabetes Mellitus/veterinary , Dog Diseases/metabolism , Monosaccharide Transport Proteins/metabolism , Muscle Proteins/metabolism , Obesity/veterinary , Animals , Biological Transport , Blotting, Western , Cell Membrane/metabolism , Diabetes Mellitus/drug therapy , Diabetes Mellitus/metabolism , Disease Models, Animal , Dog Diseases/drug therapy , Dogs , Female , Glucose Transporter Type 4 , Hypoglycemic Agents/administration & dosage , Hypoglycemic Agents/metabolism , Insulin/administration & dosage , Insulin/metabolism , Microsomes/metabolism , Monosaccharide Transport Proteins/analysis , Muscle Proteins/analysis , Obesity/metabolism , Ovariectomy/veterinaryABSTRACT
The GLUT4 transporter plays a key role in insulin-induced glucose uptake, which is impaired in insulin resistance. The objective of the present study was to investigate the tissue content and the subcellular distribution of GLUT4 protein in 4-to 12-year-old control, obese and insulin-treated diabetic mongrel female dogs (4 animals per group). The parametrial white adipose tissue was sampled and processed to obtain both plasma membrane and microsome subcellular fractions for GLUT4 analysis by Western blotting. There was no significant difference in glycemia and insulinemia between control and obese animals. Diabetic dogs showed hyperglycemia (369.9 ± 89.9 mg/dl). Compared to control, the plasma membrane GLUT4, reported per g tissue, was reduced by 55 percent (P < 0.01) in obese dogs, and increased by 30 percent (P < 0.05) in diabetic dogs, and the microsomal GLUT4 was increased by approximately 45 percent (P < 0.001) in both obese and diabetic animals. Considering the sum of GLUT4 measured in plasma membrane and microsome as total cellular GLUT4, percent GLUT4 present in plasma membrane was reduced by approximately 65 percent (P < 0.001) in obese compared to control and diabetic animals. Since insulin stimulates GLUT4 translocation to the plasma membrane, percent GLUT4 in plasma membrane was divided by the insulinemia at the time of tissue removal and was found to be reduced by 75 percent (P < 0.01) in obese compared to control dogs. We conclude that the insulin-stimulated translocation of GLUT4 to the cell surface is reduced in obese female dogs. This probably contributes to insulin resistance, which plays an important role in glucose homeostasis in dogs.
