A 5-year-old boy has developed persistent food-seeking behavior over the past few months. His mother initially thought that the boy was undergoing a growth spurt, but despite how much she fed him he never seemed satisfied. He has gained more than 4.5 kg (10 lb). The patient has also started complaining of a headache and nausea in the morning. His physical examination is significant for BMI of 32 kg/m². Temperature is 37.2 C (99 F), blood pressure is 100/70 mm Hg, pulse is 92/min, and respirations are 16/min. His pediatrician becomes concerned about possible central nervous system involvement. This patient's food-seeking behavior could be explained by a lesion causing impairment of which hypothalamic nucleus?

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11ec160b_359d_fb74_9249_27edb820214e_MD0001_00 The hypothalamus is in the diencephalon at the base of the brain. It is a key region involved in homeostasis; including the regulation of temperature, appetite, emotion, growth, and circadian rhythm. The ventromedial and lateral nuclei are involved in the regulation of food intake. The ventromedial nucleus is vital in monitoring blood glucose and mediates satiety. Lesions of this area of the hypothalamus (eg, trauma, infection, brain tumors) can result in hyperphagia and obesity. Conversely, the lateral nucleus signals hunger. Lesions can result in loss of appetite (eg, failure to thrive) (Choice B). (Choices A and C) The anterior and posterior nuclei are involved in temperature control through regulation of the autonomic nervous system. The anterior nucleus coordinates cooling via inhibition of adrenergic input, causing vasodilation and stimulation of cholinergic pathways (eg, sweating). Destruction of this nucleus can cause uncontrolled hyperthermia. Conversely, the posterior nucleus regulates heat conservation and heat production via vasoconstriction and shivering. Destruction can lead to hypothermia. (Choice D) The suprachiasmatic nucleus is located immediately above the optic chiasm and receives visual input directly from the retina. It helps regulate circadian rhythms by relaying light information to other hypothalamic nuclei and to the pineal gland. (Choice E) The supraoptic and paraventricular nuclei project axons into the posterior pituitary gland (neurohypophysis), producing vasopressin (antidiuretic hormone) and oxytocin. Oxytocin is associated with uterine contractions and milk letdown; vasopressin regulates fluid balance via reabsorption of water from the kidneys. Educational objective: The hypothalamus is a key region responsible for homeostasis. The ventromedial nucleus mediates satiety; lesions of this area of the hypothalamus can result in hyperphagia and obesity. __________ References: Role of ventromedial hypothalamus in high fat diet induced obesity in male rats: association with lipid profile, thyroid profile and insulin resistance. (http://www.ncbi.nlm.nih.gov/pubmed/25206074) Metabolic mystery: aging, obesity, diabetes, and the ventromedial hypothalamus. (http://www.ncbi.nlm.nih.gov/pubmed/23791973)

A 5-Year-Old Boy Has Developed Persistent Food-Seeking Behavior Over the Past