A number of environmental chemicals are estrogenic or androgenic, acting through synergistic interaction with the steroid-receptor complex. Until now, assays for these environmental signals have been based largely on transgenic expression systems, such as the yeast estrogen system. Here, we investigate the possibility that synergistic low dose exposure to environmental chemicals interfering with steroid-associated responses may be detectable by transient activational effects on steroid-dependent calling behavior during early development in the precocial avian model.

Dietary and systemic applications of a number of steroids reorganize the synaptic connectivities of neurons within the intercollicular area in galliform birds. These neurons seem to control the expression of at least two distinct types of calls: one isolation-induced juvenile calling pattern (distress calls), and one typically adult and male expression (crowing). After hatching, exposure of chicks to androgenic steroids leads to a sonographically clear transition from distress-calling to crowing within hours. The change in the time-frequency pattern of single calls becomes associated with a modified pattern of inter-call intervals - that is, there are previously undetected modifications in the temporal evolution of single events.

Here, we show how to register the temporal pattern of single calls by extracting event-tuning curves from real-time sonographic records. Changes in the time-resolved calling patterns, available from the evolution of call-tuning curves, seem to be highly sensitive to the onset of steroid-dependent reorganization of call-control areas. In fact, this type of time-resolved vocal analysis can signal effects that are below 'threshold' for time-frequency changes of single calls, and may be suitable for assaying the long-term action of low dose combinations of certain environmental chemicals. At the scale of behavioral motoric expressions, the present methods reflect similar aspects that have been found by introducing temporal aspects into the study of neural coding principles at the scale of single brain cell activities.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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