Environmental Modulation of Reproductive Function

Birdbrained Research

Research

Most living things use cues from the environment to time their reproductive efforts. For example, many seasonally breeding animals increase the secretion of reproductive hormones in response to lengthening days (light cues) in the spring. Other species use different kinds of cues, such as social context or food availability. How such signals are processed by the brain, and particularly how these signals are transduced into an endocrine response, is not well understood. Using a marker for new protein synthesis (Egr-1), we can map the brain’s response to cues in the lab. By studying a model organism that responds to light cues with increases in hormone release, we can see that after just one long day, the mediobasal hypothalamus, a region at the base of the brain where reproductive hormones are released into the bloodstream, is actively producing Egr-1 (see figure below). The Egr-1 indicates that this brain region is actively engaging in new gene transcription; in other words, responding to the environmental signal. 

We are currently investigating whether the mediobasal hypothalamus is involved in the reproductive response to other kinds of signals besides light. If so, then this mechanism may be important for all animals (including humans) responding to all kinds of cues. Since our model organism uses auditory communication signals from members of the same species to time reproductive development, we are playing recordings of those signals to females in the lab in order to map the brain response. We have found that within minutes, Egr-1 expression does increase, relative to controls listening to synthetic tones, in regions of the mediobasal hypothalamus known to be synthesizing protein during photo-induced hormone release (below right). We also found that reproductive hormones are released rapidly in response to the auditory signals (below left). Our results suggest that activation of this region serves as a final common pathway for both kinds of stimulation (light and sound). The research helps us to understand how the brain uses information from the external environment to cause adaptive changes in the organism, and also informs the study of human fertility by elucidating how the environment affects reproductive function in all vertebrates.

The mediobasal hypothalamus after exposure to winter-like short days (left) or one long spring-like day (right). The black dots represent the expression of Egr-1, a marker for new protein synthesis.  IN= infundibular nucleus; ME = median eminence; v.III = third ventricle.

Short days

One long day

Hearing an auditory courtship signal (yellow bars) causes new protein synthesis in the mediobasal hypothalamus (right) and the release of reproductive hormones (left). Hearing computer-generated tones (blue bars) does not have the same effects.  IN = infundibular nucleus; ME = median eminence; LH = luteinizing hormone.

This work is funded by the National Science Foundation.