oxytocin, or to altered gonadal hormone levels all have
been shown to impact social behaviors (Axelson et al. 1999;
Stribley and Carter 1999; Catalani et al. 2000; Lonstein
and De Vries 2000a; Kramer et al. 2003). Even substances
consumed by the dam can affect the social behavior of off-
spring (Kelly and Tran 1997). Given the recent evidence
that a variety of manmade chemicals in the environment can
mimic the effects of endogenous substances, the study of so-
cial behavior in rodents may become even more important
by providing a means to study the effects of anthropogenic
substances on biologically important behaviors.
Summary
Social behavior in rodents is regulated by complex inter-
actions between a number of brain regions and by a variety
of neurotransmitter systems within the central nervous sys-
tem. The combined behavioral output of these systems must
be capable of responding appropriately to a wide variety of
stimuli, not the least of which are the responses of the indi-
viduals with which an animal interacts. Research over the
past 20 years has provided a basic framework upon which
our current understanding of the neural basis of social be-
havior rests. Two loosely defined systems appear to interact
to modulate a large percentage of social interactions. The
first system may be defined as a “recognition circuit,” and
is responsible for distinguishing between individuals such
that appropriate behavioral responses, in some cases based
on past interactions, may be displayed. The second circuit,
an “incentive circuit,” may serve to determine the intensity
of the interaction. Together these circuits may act to deter-
mine the valence and /or intensity of the interaction, that
is, approach or avoidance, aggressive versus passive behav-
ior, and so forth. Ongoing research is attempting to elabo-
rate central changes underlying the formation and mainte-
nance of social bonds, the effects of perinatal influences on
adult social behavior, and the role of genetics in determin-
ing species- and individual-specific social behaviors.194 Chapter Sixteen