Light and electron microscopic immunocytochemistry of β-endorphin/β-LPH-like immunoreactive neurons in the arcuate nucleus and surrounding areas of the rat hypothalamus

β-Endorphin/β-LPH-like immunoreactive neurons in the hypothalamic arcuate nucleus and its surrounding areas were visualized by light and electron microscopic immunocytochemistry. Immunoreactive processes were found in the vicinity of the pia mater, in the lateral part of the external layer of the median eminence and near the lateral wall of the third ventricle. Neuronal perikarya contained immunoreactive dense granules as well as developed cell organellae. They received neuronal inputs from other neurons through axoplasmic and axodendritic synapses. Immunoreactive neuronal processes containing dense granules and mitochondria were found as preterminal elements on non-immunoreactive neuronal soma and dendrites. Immunoreactive processes also make intimate contact with capillaries in the arcuate nucleus near the median eminence.