ABSTRACT
Competition between adult males for limited resources such as food and receptive females is shaped by the male pattern of pituitary growth hormone (GH) secretion that determines body size and the production of urinary pheromones involved in male-to-male aggression. In the brain, dopamine (DA) provides incentive salience to stimuli that predict the availability of food and sexual partners. Although the importance of the GH axis and central DA neurotransmission in social dominance and fitness is clearly appreciated, the two systems have always been studied unconnectedly. Here we conducted a cell-specific genetic dissection study in conditional mutant mice that selectively lack DA D2 receptors (D2R) from pituitary lactotropes (lacDrd2KO) or neurons (neuroDrd2KO). Whereas lacDrd2KO mice developed a normal GH axis, neuroDrd2KO mice displayed fewer somatotropes; reduced hypothalamic Ghrh expression, pituitary GH content, and serum IGF-I levels; and exhibited reduced body size and weight. As a consequence of a GH axis deficit, neuroDrd2KO adult males excreted low levels of major urinary proteins and their urine failed to promote aggression and territorial behavior in control male challengers, in contrast to the urine taken from control adult males. These findings reveal that central D2Rs mediate a neuroendocrine-exocrine cascade that controls the maturation of the GH axis and downstream signals that are critical for fitness, social dominance, and competition between adult males.
Subject(s)
Body Size/physiology , Growth Hormone/metabolism , Pituitary Gland/metabolism , Prolactin/metabolism , Receptors, Dopamine D2/metabolism , Analysis of Variance , Animals , Benzamides/pharmacokinetics , Body Size/drug effects , Body Size/genetics , Body Weight/drug effects , Body Weight/genetics , Case-Control Studies , Catatonia/chemically induced , Catatonia/metabolism , Dopamine Antagonists/pharmacology , Eating/drug effects , Eating/genetics , Eating/physiology , Female , Haloperidol/pharmacology , Insulin-Like Growth Factor I/metabolism , Intermediate Filament Proteins/genetics , Male , Mice , Mice, Inbred C57BL , Mice, Transgenic , Nerve Tissue Proteins/genetics , Nestin , Oligodeoxyribonucleotides, Antisense/pharmacology , Pheromones/urine , Pituitary Gland/drug effects , Prolactin/genetics , Protein Binding/drug effects , Protein Binding/genetics , Proteins/metabolism , Radioimmunoassay , Receptors, Dopamine D2/deficiency , Receptors, Dopamine D2/genetics , Social Dominance , Territoriality , Tritium/pharmacokineticsABSTRACT
Obesity is a chronic metabolic disorder affecting half a billion people worldwide. Major difficulties in managing obesity are the cessation of continued weight loss in patients after an initial period of responsiveness and rebound to pretreatment weight. It is conceivable that chronic weight gain unrelated to physiological needs induces an allostatic regulatory state that defends a supranormal adipose mass despite its maladaptive consequences. To challenge this hypothesis, we generated a reversible genetic mouse model of early-onset hyperphagia and severe obesity by selectively blocking the expression of the proopiomelanocortin gene (Pomc) in hypothalamic neurons. Eutopic reactivation of central POMC transmission at different stages of overweight progression normalized or greatly reduced food intake in these obesity-programmed mice. Hypothalamic Pomc rescue also attenuated comorbidities such as hyperglycemia, hyperinsulinemia, and hepatic steatosis and normalized locomotor activity. However, effectiveness of treatment to normalize body weight and adiposity declined progressively as the level of obesity at the time of Pomc induction increased. Thus, our study using a novel reversible monogenic obesity model reveals the critical importance of early intervention for the prevention of subsequent allostatic overload that auto-perpetuates obesity.
