Neural Substrates of Sexual Motivation and Performance as Revealed by Neural Immediate-Early Gene Expression

Re: Neuronal Colocalization of Androgen Receptor and, Mating-Induced Fos: Hormone-sensitive Neurons Link Spinal, Cord, Midbrain, and Forebrain Structures Regulating, C

on behalf of D Edwards

On Sat Dec 12, michael baum wrote
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>You show nicely that there is considerable overlap in the population of neurons at all levels of the 'mating circuit' (ranging from spinal cord to preoptic area) which are Androgen receptor containing and which express Fos after mating. What about the correspondence between AR-containing cells and odor-induced Fos--esp. in the medial amygdala and BNST?

Michael,

I tried to use the REPLY box on the toolbar so that this response would
be posted with your message. I then clicked on SUBMIT to post it but
nothing good happens. So, I'll send this directly to you and try again
to post it later (if you have a helpful hint about this please pass it
on).

There is correspondence (i.e., Fos found in AR neurons) in these two
structures (and in the MPN as well) where we have reason to believe that
Fos expression is increased as a consequence of exposure to odors from
receptive females, but I am cautious about saying the Fos-expression is
"odor-induced."

In some of our studies we have what we call "Social Controls." These
are males placed with a receptive female where physical contact is
prevented by a wire mesh divider which separates the testing jar into
two compartments. These males are tested at the same time as males who
are allowed to mate normally, and they're killed within a few minutes of
the mated males so that the duration of the tests for the mated males
and the Social Controls is nearly identical. Although the barrier
prevents prevents mating, a typical male in this situation will show 4-5
penile erections in the first 30 minutes of the test session. For
convenience call these noncontact erections (NCE). Fos-ir neurons in
brain and spinal cord vary according to group -- Mated Males Social
Controls Isolated males. For Social Controls, as for Mated males, the
vast majority (85%)of the Fos-ir neurons are also AR-ir (at least for
the areas of brain and spinal cord where we have counted them).

We know from work that Ben Sachs has done that volatile odors from
estrous females are necessary and sufficient to elicit NCEs. And he has
evidence that the MNA and BNST are important parts of the central
olfactory pathway through which volatile odors elicit NCE. So, it's
easy to imagine that the enhanced Fos expression in the MNA and BNST
relative to isolated males is "odor-induced." But what does one say
about the elevated Fos expression in the spinal cord? Well, that
probably results from somatosensory input related to erection and/or the
penile grooming associated with it (although we cannot discount the
possibility of a contribution via brain afferents to the cord). But the
erections themselves surely reflect some degree of brain-mediated sexual
arousal, perhaps correlated with Fos expression in different brain
regions. And to the extent that sexual arousal is enhanced by erection
and/or the penile grooming that accompanies it we may expect an
additional enhancement of Fos expression in the same brain structures.

The point of this rather long response is that I don't think we have yet
clearly discriminated Fos expression that is odor-induced from that
which results from behavior and/or the sexual arousal which forms the
basis it.

--
David A. Edwards
Department of Psychology

Mon Dec 14