Metamodulation of the biogenic @entity4478 : second-order modulation by @entity134 hormones and XXXX cocktails.

@entity4079 @entity935 @entity6115 @entity4478 @entity11879 @entity134 @entity11088 @entity750
An evolutionarily conserved feature of neural systems is that they can be modified by neuromodulators. These modulatory chemical signals include the biogenic @entity4478 , @entity11879 (OA), @entity750 ( @entity750 ) and @entity935 (DA). Such modulation effectively broadens the operational range in which specific neural circuits can function adaptively. This report discusses how these @entity4478 are themselves modulated; for example, by the @entity134 hormone @entity11088 (20-E) or by the addition of a second biogenic @entity6115 . Such second-order neuromodulation, termed metamodulation, is discussed in the context of two well-studied invertebrate systems: the @entity4079 moth @entity4079 , a model of neurodevelopment and plasticity, and the medicinal leech Hirudo medicinalis, a long-favored preparation used to study neural circuits at the level of identified neurons. A portion of this article reviews our previous research of @entity4079 that shows that the 'preadult' rise in 20-E is both necessary and sufficient for the increased levels of @entity11879 observed in the adult. Such elevated levels likely play an important role in the production and modulation of adult behaviors. The somatic growth of median octopaminergic neurons and the late expression of OA-immunoreactivity by novel lateral neurons are also demonstrated to be dependent on 20-E. New immunocytochemical results of stained dopaminergic neurons in the larval and adult moth brain are provided as well, and the potential influence of 20-E on the developmental expression of this neuromodulator is presented. Turning attention to the leech, data indicate that the actions of OA are dramatically altered when @entity750 is combined with OA in the bath surrounding the isolated nervous system. Although either OA or @entity750 alone induces fictive swimming behavior, a cocktail of these two @entity4478 strongly inhibits the generation of swimming. Subsequent removal of such a mixture induces nearly continuous swimming and constitutes the best swim-inducing stimulus encountered to date. To understand better how these nonadditive effects are achieved, new results are discussed that indicate that the leech brain is the target of metamodulation by the two @entity4478 . Both the arthropod and annelid systems presented here highlight the multiple levels of metamodulation that can exist in nervous systems, and the diverse ways that a modulator's actions can become altered over short or long time periods.
