The Journal of Neuroscience, September 15, 1999, 19(18):8027-8035
Maternal Aggression Is Reduced in Neuronal Nitric Oxide
Synthase-Deficient Mice
Stephen C.
Gammie and
Randy J.
Nelson
Departments of Psychology and Neuroscience, Behavioral
Neuroendocrinology Group, The Johns Hopkins University, Baltimore, MD
21218
Lactating females express rapid extremes in behavior, ranging from
gentle nurturance toward offspring to fiercely protective aggression
against intruders. Although males often behave aggressively against
intruders, female rodents usually express aggression only when rearing
and protecting pups. Nitric oxide (NO) inhibits male aggression;
however, its role in maternal aggression is unknown. In the present
study, female mice with targeted disruption of the neuronal nitric
oxide synthase gene (nNOS
/
) displayed significant deficits in
maternal aggression relative to wild-type (WT) mice in terms of
percentage displaying aggression, the average number of attacks against
a male intruder, and the total time spent attacking the male intruder.
The nNOS
/
mice displayed normal pup retrieval behavior. Because the
specific deficits in maternal aggression in the nNOS
/
mice
suggested a possible role for NO in maternal aggression, we combined
behavioral testing of WT mice with immunohistochemistry for citrulline,
an indirect marker of NO synthesis, to examine indirectly NO synthesis
during maternal aggression. A significant increase in the number of
citrulline-positive cells was identified in the medial preoptic
nucleus, the suprachiasmatic nucleus, and the subparaventricular zone
regions of the hypothalamus in aggressive lactating females relative to
control mice. In other regions of the brain, no changes in the number
of citrulline-positive cells were observed across either groups or
treatments. These results provide two indirect lines of evidence that
NO release is associated with maternal aggression.
Key words:
nitric oxide; neuronal nitric oxide synthase; maternal aggression; citrulline; hypothalamus; mice
Copyright © 1999 Society for Neuroscience 0270-6474/99/19188027-09$05.00/0