Age- and hormone-regulation of opioid peptides and synaptic proteins in the rat dorsal hippocampal formation.

Circulating estrogen levels and hippocampal-dependent cognitive functions decline with aging. Moreover, the responses of hippocampal synaptic structure to estrogens differ between aged and young rats. We recently reported that estrogens increase levels of post-synaptic proteins, including PSD-95, and opioid peptides leu-enkephalin and dynorphin in the hippocampus of young animals. However, the influence of ovarian hormones on synaptic protein and opioid peptide levels in the aging hippocampus is understudied. Here, young (3- to 5-month-old), middle-aged (9- to 12-month-old), and aged (about 22-month-old) female rats were ovariectomized and then, 4 weeks later, subcutaneously implanted with a silastic capsule containing vehicle or 17ß-estradiol. After 48 h, rats were subcutaneously injected with progesterone or vehicle and sacrificed 1 day later. Coronal sections through the dorsal hippocampus were processed for quantitative peroxidase immunohistochemistry of leu-enkephalin, dynorphin, synaptophysin, and PSD-95. With age, females showed opposing changes in leu-enkephalin and dynorphin levels in the mossy fiber pathway, particularly within the hilus, and regionally specific changes in synaptic protein levels. 17ß-estradiol, with or without progesterone, altered leu-enkephalin levels in the dentate gyrus and synaptophysin levels in the CA1 of young but not middle-aged or aged females. Additionally, 17ß-estradiol decreased synaptophysin levels in the CA3 of middle-aged females. Our results support and extend previous findings indicating 17ß-estradiol modulation of hippocampal opioid peptides and synaptic proteins while demonstrating regional and age-specific effects. Moreover, they lend credence to the "window of opportunity" hypothesis during which hormone replacement can modulate hippocampal structure and circuitry to improve cognitive outcomes.

Cellular and subcellular localization of estrogen and progestin receptor immunoreactivities in the mouse hippocampus.

Estrogen receptor-alpha (ERalpha), estrogen receptor-beta (ERbeta), and progestin receptor (PR) immunoreactivities are localized to extranuclear sites in the rat hippocampal formation. Because rats and mice respond differently to estradiol treatment at a cellular level, the present study examined the distribution of ovarian hormone receptors in the dorsal hippocampal formation of mice. For this, antibodies to ERalpha, ERbeta, and PR were localized by light and electron immunomicroscopy in male and female mice across the estrous cycle. Light microscopic examination of the mouse hippocampal formation showed sparse nuclear ERalpha and PR immunoreactivity (-ir) most prominently in the CA1 region and diffuse ERbeta-ir primarily in the CA1 pyramidal cell layer as well as in a few interneurons. Ultrastructural analysis additionally revealed discrete extranuclear ERalpha-, ERbeta-, and PR-ir in neuronal and glial profiles throughout the hippocampal formation. Although extranuclear profiles were detected in all animal groups examined, the amount and types of profiles varied with sex and estrous cycle phase. ERalpha-ir was highest in diestrus females, particularly in dendritic spines, axons, and glia. Similarly, ERbeta-ir was highest in estrus and diestrus females, mainly in dendritic spines and glia. Conversely, PR-ir was highest during proestrus, mostly in axons. Except for very low levels of extranuclear ERbeta-ir in mossy fiber terminals in mice, the labeling patterns in the mice for all three antibodies were similar to the ultrastructural labeling found previously in rats, suggesting that regulation of these receptors is well conserved across the two species.

Ultrastructural localization of extranuclear progestin receptors relative to C1 neurons in the rostral ventrolateral medulla.

To better understand the role of progestins in the C1 area of the rostral ventrolateral medulla (RVLM), immunocytochemical localization of progestin receptors (PRs) was combined with tyrosine hydroxylase (TH) in single sections of RVLM from proestrus rat brains prepared for light and electron microscopy. By light microscopy, PR-immunoreactivity (-ir) was detected in a few nuclei that were interspersed between TH-labeled perikarya and dendrites. Electron microscopy revealed that PR-ir was in several extranuclear locations. The majority of PR-labeling was in non-TH immunoreactive axons (51+/-9%) near the plasma membrane. Additional dual labeling studies revealed that PR-immunoreactive axons could give rise to terminals containing the GABAergic marker GAD65. PR-ir also was found in non-neuronal processes (29+/-9%), some resembling astrocytes. Occasionally, PR-ir was in non-TH-labeled terminals (10+/-3%) affiliated with clusters of small synaptic vesicles, or in patches contained in the cytoplasm of dendrites (10+/-1%). These findings suggest that progestins can primarily modulate neurons in the C1 area of the RVLM by presynaptic mechanisms involving GABAergic transmission. Moreover, they suggest that PR activation may contribute to progestin's effects on arterial blood pressure during pregnancy as well as to sex differences in central cardiovascular regulation.