| Summary: | Both feeding and sexual behaviour play a major role in the survival of a
species. Research has revealed that there may be an antagonistic relationship
between these two behaviours. For example, in times of limited food availability,
priorities in energy partitioning favour individual survival (i.e., searching for food)
over reproduction. Further, there appear to be significant interactions between
the neuroendocrine control of reproduction and the regulation of energy balance.
Research investigating the central sites that regulate sexual and feeding
behaviour has shown the hypothalamus to be of prime importance for both these
behaviours. Further, serotonin (5-HT) and norepinephrine (NE) have been
shown to influence copulatory activity and food consumption in rats. There has
been a considerable amount of controversy as to the relative involvement of
different 5-HT receptor subtypes in both sexual and feeding behaviour. This
thesis focusses on the importance of the 5-HT2 receptor subtype in feeding and
copulation in the male rat.
Experiments 1-3 were conducted in order to establish whether there is a
natural relationship between sexual and feeding behaviour in the male rat. In
these experiments, the involvement of 5-HT2 receptors was investigated by
recording the display of wet dog shakes, a behavioural indicator of 5-HT2
activity. These experiments revealed that there may be a relationship between
the natural level of sexual activity and feeding behaviour, and this may be due to
an endogenous difference in 5-HT2 receptors.
Experiments 4-9 were developed to investigate the specific receptor
subtype important for the inhibition of sexual responding and feeding behaviour
by 1-(2,5-dimethoxy-4-iodophenyl aminopropane) (DOI), a 5-HT₂/1C receptor
agonist. By employing selective 5-HT₂ antagonists, it was revealed that while 5-HT₂ receptors appear to be of prime importance in sexual activity in the male
rat, they are not as important in feeding behaviour. It may be that DOIs activity
at 5-HT₁c receptors are more important for its influence on feeding behaviour
than it's affect at 5-HT₂ receptors, while the reverse may be true of sexual
responding. Further, 5-HT may be less important in feeding than copulation as a
larger dose of DOI was required to inhibit feeding than that used in sexual
behaviour experiments.
Taken together, these studies suggest that while 5-HT appears to be
involved in both feeding and sexual responding, 5-HT may be more important in
the regulation of sexual responding than in feeding behaviour and different
receptor subtypes may mediate the influence of this neurotransmitter on feeding
and copulatory activity.
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