Estrogen Receptor Expression in Laryngeal Muscle in Relation to Estrogen-Dependent Increases in Synapse Strength

Abstract

In Xenopus laevis, the laryngeal neuromuscular synapse is the final effector for sexually differentiated song production. Females have stronger laryngeal synapses than males, and synapse strength is estrogen dependent. Estrogen-induced increases in synaptic strength require at least 3 weeks of exposure, suggesting that the hormone acts via a classical genomic mechanism involving the estrogen receptor (ER). The locus of the sex difference in synapse strength, determined using quantal analysis, is presynaptic, leading to the prediction that estrogen acts directly on vocal motor neurons. However, laryngeal motor neurons do not accumulate estrogen. Estrogen might instead affect motor neuron transmitter release via a retrograde signal from its target muscle. To test this hypothesis, we determined whether laryngeal muscle expresses ER. With RT-PCR using primers that recognize highly conserved domains of the ERα, mRNA products of the predicted size were amplified from laryngeal muscle as well as from other classical target tissues (forebrain and oviduct). Northern blots using a portion of the PCR product as primer revealed the same-sized band in oviduct and laryngeal muscle. Immunocytochemistry and Western blots confirmed the presence of ER protein in laryngeal muscle fibers and revealed several proteins in laryngeal muscle, brain and liver; among these was an approximately 66-kD protein – presumed to be full-length ER – that was the only one found in oviduct. Estrogen treatment of juveniles resulted in an upregulation of the 66-kD ER protein concomitant with an increase in quantal content. Taken together, these experiments strongly suggest that the ER is expressed by laryngeal muscle; this receptor could mediate estrogen-dependent changes in synaptic strength via retrograde signaling.

Differences in neuromuscular junctions of laryngeal and limb muscles in rats

“…This may reflect possible correlates of higher synapse strength with the specialized NMJ clusters. In support of this concept, synapse strength of laryngeal muscles is higher in females and can be increased by the female hormone, estrogen 28, 29. In our study, the TA muscle in female rats had more AChR clusters than in male rats, which strongly suggests a correlation between larger numbers of AChR clusters and higher synapse strength.…”

Estrogenic support of motoneuron dendritic growth via the neuromuscular periphery in a sexually dimorphic motor system

“…While neonatal BC/LA muscles express androgen receptors (Fishman et al, 1990), the presence of estrogen receptors during postnatal development has not been demonstrated. Additionally, muscle cells may not be the only possible estrogen target in the neuromuscular periphery, as estrogen receptors have been located within Schwann cells (Jung-Testas et al, 1993) and at neuromuscular junctions (Wu et al, 2003). Subsequent descriptive studies of the type(s) of estrogen receptors present, and on what specific cells and cellular parts in the neuromuscular periphery, will be required in order to fully describe the site(s) and mechanism(s) of estrogenic action.…”

Histopathological effects of estrogen deficiency on larynx mucosa in ovariectomised rats

“…A significant number of sex steroid receptors have been detected in human larynx tissues [3,10,11] suggesting a probable effect of these hormones on phonatory function and justifying their specific role in the development of the larynx [12]. During childhood the ovaries are not producing significant amounts of sex hormones as a result of hypothalamic and pituitary suppression.…”