Estrogen receptor-α and -β immunoreactive neurons in the brainstem and spinal cord of male and female mice: Relationships to monoaminergic, cholinergic, and spinal projection systems

For many populations of estrogen-sensitive neurons it remains unknown how they are associated with central nervous system circuitries that mediate estrogen-induced modulation of behavioral components. With the use of double-labeling immunohistochemistry and tracing techniques, the relationships of estrogen receptor (ER)-α- and ER-β-immunoreactive (IR) neurons in the mouse brainstem and spinal cord to monoaminergic, cholinergic, and spinal projection systems are explored. Similar distributions of ER-IR neurons were present in females and males, with differences in labeling intensity of ER-α immunoreactivity among males and estrogen-, and oil-treated females. Barrington's nucleus, the ventrolateral medulla, and the nucleus of the solitary tract contained spinal-projecting ER-α-IR neurons, whereas ER-α-IR neurons in the periaqueductal gray, parabrachial nucleus, and catecholaminergic A1 cell group received spinal input. Numerous tyrosine hydroxylase (TH)-IR ER-α-IR neurons were present in the ventral periaqueductal gray, nucleus of the solitary tract, A1 cell group, and lumbosacral cord. The dorsal raphe nucleus contained ER-α-IR and ER-β-IR neurons that colocalized with serotonin (5HT), and the reticulotegmental nucleus contained 5HT-IR ER-α-IR neurons. Fibers IR for vesicular acetylcholine transporter (VAChT), TH, and 5HT were located among ER-α-IR neurons in the dorsal horn and spinal autonomic regions. Robust staining for TH and VAChT, but not 5HT, was present among ER-α-IR neurons in the lumbosacral lateral collateral pathway. Possible modulatory actions of estrogen on each of these ER-IR populations are discussed in the context of their specific function, including micturition, sexual behavior, ejaculation, cardiovascular and respiratory control, tactile and nociceptive sensory processing, anti-nociception, endocrine regulation, and feeding.