Stress Affects a Gastrin-Releasing Peptide System in the Spinal Cord That Mediates Sexual Function: Implications for Psychogenic Erectile Dysfunction

Many men suffering from stress, including post-traumatic stress disorder (PTSD), report sexual dysfunction, which is traditionally treated via psychological counseling. Recently, we identified a gastrin-releasing peptide (GRP) system in the lumbar spinal cord that is a primary mediator for male reproductive functions.To ask whether an acute severe stress could alter the male specific GRP system, we used a single-prolonged stress (SPS), a putative rat model for PTSD in the present study. Exposure of SPS to male rats decreases both the local content and axonal distribution of GRP in the lower lumbar spinal cord and results in an attenuation of penile reflexes in vivo. Remarkably, pharmacological stimulation of GRP receptors restores penile reflexes in SPS-exposed males, and induces spontaneous ejaculation in a dose-dependent manner. Furthermore, although the level of plasma testosterone is normal 7 days after SPS exposure, we found a significant decrease in the expression of androgen receptor protein in this spinal center.We conclude that the spinal GRP system appears to be a stress-vulnerable center for male reproductive functions, which may provide new insight into a clinical target for the treatment of erectile dysfunction triggered by stress and psychiatric disorders

Stress-response of the GRP system in the upper lumbar spinal cord.

<p>(A, B) The number of GRP-immunoreactive neurons was greater in control males than in females in the upper lumbar spinal cord (L3–4). In contrast to overall concentrations of GRP, no significant difference between control and SPS-exposed males was observed in the number of GRP-immunoreactive neurons (B). However, the density of immunoreactive dendrites was decreased (A). Scale bar, 100 µm.</p

Stress-response of the GRP system in the lower lumbar spinal cord.

<p>(A–D) ICC reveals a sexual dimorphism in GRP-immunoreactive fiber distribution in lower lumbar spinal cord autonomic nuclei, as males have more GRP-immunoreactive fibers in the SPN (magenta inset) and the DGC than do females. SPS-exposure decreased the distribution of GRP-immunoreactive fibers (B), but not nNOS expression (C), to a level intermediate between control males and females (E). nNOS serves as a marker for autonomic preganglionic neurons, and double ICC reveals close appositions of GRP containing fibers with the cell bodies and proximate dendrites of nNOS-immunoreactive neurons in the SPN (D). GRP-immunoreactive fibers in a non-autonomic region of the spinal cord, the DH, are equivalent in males, females and SPS-exposed males (E). *<i>P</i><0.01 compared with control males. Scale bars, 200 µm (A); 50 µm (D).</p

Stress affects the expression of AR and ERα protein in the upper lumbar spinal cord after SPS exposure.

<p>Representative Western immunoblot results are shown in (A). The calculated ODs of the protein bands corresponding to AR and ERα protein were normalized to each GAPDH OD and expressed as a ratio (B). The expression of AR, but not ERα, protein in the upper lumbar spinal cord (L3–4) was significantly decreased 7 days after SPS exposure (B). *<i>P</i><0.05 compared with control males.</p

Stress and GRP involvement in male sexual reflexes.

<p>(A) SPS-exposure in male rats reduces spinal reflexes of the penis, including simple erections and cup-like flaring erections of the distal glans. Systemic treatment of SPS-exposed males with a specific agonist for GRP-R (rGRP_20–29) restores erections and appears to affect cups and flips. (B) Spontaneous ejaculations during tests for penile reflexes are also increased by systemic rGRP_20–29 treatment in a dose-dependent manner. *<i>P</i><0.05 compared with control males. †<i>P</i><0.05 compared to SPS-exposed males. Data are presented as means±s.e.m. (A); and as % (B).</p

Sex difference and stress-response of GRP spinal neurons.

<p>(A) Schematic drawing summarizing the GRP system in the lumbar spinal cord that controls male reproductive functions <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004276#pone.0004276-Sakamoto1" target="_blank">[20]</a>. Using a competitive ELISA for GRP, we quantified the local contents of GRP in two separate regions of the lumbar spinal cord by dividing the lumbar spinal cord into the upper (L3–4; somal region of GRP neurons; A–C) and lower (L5–6; axonal region of GRP neurons; A, B, D) spinal regions. Both in the upper and lower lumbar spinal cord, the concentrations of GRP in control males was greater than that in females (E, F). Seven days after SPS exposure, in males, GRP was significantly reduced in both the upper and lower lumbar spinal cord (E, F). *<i>P</i><0.05 compared with control males. Scale bars, 1 mm (B); 100 µm (C); 200 µm (D). AR, androgen receptor; GRP-R, GRP receptor; SNB, spinal nucleus of the bulbocavernosus; SPN, sacral parasympathetic nucleus.</p

Stress does not have a prolonged effect on circulating steroid hormones.

<p>Plasma concentrations of T (A) and CORT (B) in male rats were not significantly different 7 days after SPS exposure.</p