The release of thyroid stimulating hormone i.e. TSH from  the anterior pituitary will be decreased and in turn thyroid glands will not release thyroxine in adequate amounts.
Explanation:
Hypothalamus secretes certain hormones that triggers the release of certain hormones from the pituitary glands. Among these hypothalamic hormones , Thyrotropin releasing hormone (TRH) is responsible for stimulating the release of TSH and prolactin from anterior pituitary. If hypothalamic cells are damaged ,TRH Â will not be released and thus TSH and thyroid hormone secretion will also decrease.