Journal of Neuroscience, Vol 15, 6619-6630, Copyright © 1995 by Society for Neuroscience
Altered sexual partner preference in male ferrets given excitotoxic lesions of the preoptic area/anterior hypothalamus
RG Paredes and MJ Baum
Department of Biology, Boston University, Massachusetts 02215, USA.
Numerous experiments suggest that perinatal exposure of male vertebrates to
testosterone (T), or its estrogenic metabolites, masculinizes aspects of
coital function, including males' characteristic preference to seek out and
mate with a female as opposed to another male conspecific. Other research
has shown that this perinatal action of sex steroids also masculinizes
aspects of neuronal morphology in the medial preoptic area/anterior
hypothalamus (mPOA/AH). We asked whether neurons of the mPOA/AH contribute
to males' preference to mate with a female. The ferret is an ideal species
in which to ask this question. When tested in a T-maze after gonadectomy
and treatment with estradiol benzoate (EB), female ferrets prefer to
approach and receive neck grips from a stimulus male whereas males prefer
to approach and neck grip an estrous female. In the minority of trials when
EB-treated males approach a stimulus male, they occasionally receive a neck
grip to which they display receptive postures as opposed to agonistic
behaviors. In Experiment 1 castrated, EB-treated male ferrets which
received bilateral infusions of the NMDA excitotoxin, quinolinic acid aimed
at the dorsomedial POA/AH, preferred to approach a stimulus male
significantly more often than groups of control males which either received
a sham lesion, received a unilateral mPOA/AH lesion or in which bilateral
infusions of quinolinic aci produced no histologically detectible
excitotoxic damage to the mPOA/AH. Males with bilateral mPOA/AH lesions
also displayed neck gripping on a significantly lower percentage of trials
than control males when they approached the stimulus female.
Ovariectomized, EB-treated female ferrets with bilateral mPOA/AH lesions,
like control females, preferred to approach and receive neck grips from a
stimulus male. The males used in Experiment 1 had never experienced
circulating levels of T characteristic of the breeding season. Therefore,
in Experiment 2 prepubertally gonadectomized males and females were treated
chronically with a high dose of T propionate (TP) and tested several times
with a receptive female prior to brain surgery. Males which received
bilateral excitotoxic lesions of the mPOA/AH neck gripped and mounted
stimulus females significantly less than control males. Again, when given
EB followed by T-maze tests of partner preference, males with bilateral
mPOA/AH lesions, like sham-operated female controls, preferred to approach
the sexually active stimulus male significantly more often than control
males, which preferred to approach the stimulus female. Our results suggest
that neurons in the mPOA/AH play an important role in the integration of
sensory cues which determine heterosexual partner preference in the male
ferret, in addition to facilitating masculine coital performance.