Pars tuberalis cells that contain stainable luteinizing hormone (LH) and thyrotropin have been observed in several species. In regard to neuroendocrine regulation, electrical stimulation of the hippocampus can modify pituitary secretion of LH, and the morphology of the synaptic input from hippocampus to preoptic area differs between sexes in the rat. In contrast, gonadotrophs may be either monohormonal or bihormonal, secreting LH and/or follicle-stimulating hormone (FSH), and there are species differences as regards the relative proportions of these monohormonal and bihormonal gonadotrophs. Although the coexistence of LH and FSH in one gonadotroph was initially surprising, each hormone contains one subunit that occurs in the other hormone. Fiber tracts that connect the hypothalamus with the hypophysis are very important in neuroendocrinology. The hypothalamus mediates the linkage between neuronal functions of the limbic system and the hormonal functions of the hypophysis.