Estrogen plays a profound role in regulating the structure and function of many neuronal systems in the adult rat brain. The actions of estrogen were thought to be mediated by a single nuclear estrogen receptor (ER) until the recent cloning of a novel ER (ER-beta). To ascertain which ER is involved in the regulation of different brain regions, the present study compared the distribution of the classical (ER-alpha) and novel (ER-beta) forms of ER mRNA-expressing neurons in the central nervous system (CNS) of the rat with in situ hybridization histochemistry. Female rat brain, spinal cord, and eyes were frozen, and cryostat sections were collected on slides, hybridized with [35S]-labeled antisense riboprobes complimentary to ER-alpha or ER-beta mRNA, stringently washed, and opposed to emulsion. The results of these studies revealed the presence of ER-alpha and ER-beta mRNA throughout the rostral-caudal extent of the brain and spinal cord. Neurons of the olfactory bulb, supraoptic, paraventricular, suprachiasmatic, and tuberal hypothalamic nuclei, zona incerta, ventral tegmental area, cerebellum (Purkinje cells), laminae III-V, VIII, and IX of the spinal cord, and pineal gland contained exclusively ER-beta mRNA. In contrast, only ER-alpha hybridization signal was seen in the ventromedial hypothalamic nucleus and subfornical organ. Perikarya in other brain regions, including the bed nucleus of the stria terminalis, medial and cortical amygdaloid nuclei, preoptic area, lateral habenula, periaqueductal gray, parabrachial nucleus, locus ceruleus, nucleus of the solitary tract, spinal trigeminal nucleus and superficial laminae of the spinal cord, contained both forms of ER mRNA. Although the cerebral cortex and hippocampus contained both ER mRNAs, the hybridization signal for ER-alpha mRNA was very weak compared with ER-beta mRNA. The results of these in situ hybridization studies provide detailed information about the distribution of ER-alpha and ER-beta mRNAs in the rat CNS. In addition, this comparative study provides evidence that the region-specific expression of ER-alpha, ER-beta, or both may be important in determining the physiological responses of neuronal populations to estrogen action.

Comparative distribution of estrogen receptor-alpha and -beta mRNA in the rat central nervous system.

The distribution of cells that express mRNA encoding the androgen (AR) and estrogen (ER) receptors was examined in adult male and female rats by using in situ hybridization. Specific labeling appeared to be largely, if not entirely, localized to neurons. AR and ER mRNA-containing neurons were widely distributed in the rat brain, with the greatest densities of cells in the hypothalamus, and in regions of the telencephalon that provide strong inputs in the medial preoptic and ventromedial nuclei, each of which is thought to play a key role in mediating the hormonal control of copulatory behavior, as well as in the lateral septal nucleus, the medial and cortical nuclei of the amygdala, the amygdalohippocampal area, and the bed nucleus of the stria terminalis. Heavily labeled ER mRNA-containing cells were found in regions known to be involved in the neural control of gonadotropin release, such as the anteroventral periventricular and the arcuate nuclei, but only a moderate density of labeling for AR mRNA was found over these nuclei. In addition, clearly labeled cells were found in regions with widespread connections throughout the brain, including the lateral hypothalamus, intralaminar thalamic nuclei, and deep layers of the cerebral cortex, suggesting that AR and ER may modulate a wide variety of neural functions. Each part of Ammon's horn contained AR mRNA-containing cells, as did both parts of the subiculum, but ER mRNA appeared to be less abundant in the hippocampal formation. Moreover, AR and ER mRNA-containing cells were also found in olfactory regions of the cortex and in both the main and accessory olfactory bulbs. AR and ER may modulate nonolfactory sensory information as well since labeled cells were found in regions involved in the central relay of somatosensory information, including the mesencephalic nucleus of the trigeminal nerve, the ventral thalamic nuclear group, and the dorsal horn of the spinal cord. Furthermore, heavily labeled AR mRNA-containing cells were found in the vestibular nuclei, the cochlear nuclei, the medial geniculate nucleus, and the nucleus of the lateral lemniscus, which suggests that androgens may alter the central relay of vestibular and auditory information as well. However, of all the regions involved in sensory processing, the heaviest labeling for AR and ER mRNA was found in areas that relay visceral sensory information such as the nucleus of the solitary tract, the area postrema, and the subfornical organ. We did not detect ER mRNA in brainstem somatic motoneurons, but clearly labeled AR mRNA-containing cells were found in motor nuclei associated with the fifth, seventh, tenth, and twelfth cranial nerves. Similarly, spinal motoneurons contained AR but not ER mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

https://onlinelibrary.wiley.com/doi/pdf/10.1002/cne.902940107

Distribution of androgen and estrogen receptor mRNA‐containing cells in the rat brain: An in situ hybridization study

Hypothalamic Integration: Organization of the Paraventricular and Supraoptic Nuclei

I. Introduction II. Mechanisms of Estrogen Action A. “Genomic” and “nongenomic” mechanisms B. Steroid hormone actions on gene expression C. Subtypes of estrogen receptors D. Steroid hormone actions on putative receptors on membranes E. Rapid actions of steroids on neuronal excitability F. Steroid hormone actions via second messengers G. Neuroprotective effects of estrogens H. Summary III. Areas of the Brain Affected Outside of the Hypothalamus A. Studies of hypothalamic and extrahypothalamic actions of estrogens B. Estrogens and the cholinergic system C. Estrogens and the serotonergic system D. Catecholaminergic neurons E. Spinal cord F. Hippocampus G. Glial cells, endothelial cells, and the blood-brain barrier H. Summary IV. Effects of Estrogens on Learning and Memory V. Estrogens, Neuroprotection, and Alzheimer’s Disease VI. Conclusions

Estrogen actions in the central nervous system.

Two hours following intraperitoneal injection, estradiol-H3 is concentrated by cells in a system of limbic and hypothalamic structures. Preoptic-hypothalamic nuclei containing estrogen-concentrating cells include the medial preoptic area, medial anterior hypothalamus, ventromedial nucleus, arcuate nucleus and ventral premammillary nucleus. Limbic structures include the medial and cortical nuclei of the amygdala, lateral septum, bed nucleus of the stria terminalis, diagonal band of Broca, olfactory tubercle, ventral hippocampus, and prepiriform and entorhinal cortex. Labelled cells were also found in the lateral and ventrolateral portions of the mesencephalic central grey. Compared to these regions, most other regions of the nervous system, including the spinal cord, have very small numbers of labelled cells, which are relatively weakly labelled, and are not found in regular, specific locations. The distribution of estrogen-concentrating cells determined with the present autoradiographic method agrees with previous autoradiographic conclusions and with biochemical results from cell fractionation experiments.

The locations of estrogen-concentrating cells coincide in several brain regions with locations of estrogen-dependent neuroendocrine control mechanisms, as determined by brain implants, lesions, electrical stimulation, and electrophysiological recording. Moreover, experimental neuroanatomical studies have provided evidence for several pathways connecting regions which concentrate radioactive estradiol. Taken together, the evidence suggests a limbic-hypothalamic system of estrogen-concentrating neurons which participate in the control of mating behavior and of gonadotrophin release from the pituitary.

Atlas of estradiol-concentrating cells in the central nervous system of the female rat.

Earlier autoradiographic work resulted in the description of a limbic-hypothalamic system of cells in the female rat brain, which concentrated estradiol-H3 more highly than cells elsewhere in the brain (Pfaff, 1968a). This description was supported by scintillation counting of finely dissected brain regions after systemic estradiol-H3 injection (McEwen and Pfaff, 1970). The initial autoradiographic approach employed a combination of fixatives — formalin and osmium tetroxide — which had been found successful in preventing tritiated sex steroid translocation in thin brain sections. In the present experiment a new autoradiographic procedure, involving the direct mounting of unfixed, un-embedded frozen sections to emulsion-coated slides, was used to test the earlier conclusion that cells in certain limbic and medial hypothalamic structures show the highest estradiol retention in rat brain.

Melvyn Keiner

Papers

Atlas of estradiol-concentrating cells in the central nervous system of the female rat.

Estradiol-Concentrating Cells in the Rat Amygdala as Part of a Limbic-Hypothalamic Hormone-Sensitive System