Imagine a poison was ingested that destroyed the hypothalamic cells that produce TRH (thyroid-releasing hormone). The effects on the anterior pituitary and thyroid glands would result in

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 will not be released and thus TSH and thyroid hormone secretion will also decrease.