Two studies investigated the transfer of respondent elicitation through equivalence classes. In Experiment 1, match-to-sample procedures were used to teach 8 subjects two four-member equivalence classes. One member of one class was then paired with electric shock, and one member of the other class was presented without shock. All remaining stimuli were then presented. Using skin conductance as the measure of conditioning, transfer of conditioning was demonstrated in 6 of the 8 subjects. In Experiment 2, similar procedures were used to replicate the results of Experiment 1 and investigate the transfer of extinction. Following equivalence training and conditioning to all members of one class, one member was then presented in extinction. When the remaining stimuli from this class were then presented, they failed to elicit skin conductance. In the final phase of the experiment, the stimulus that was previously presented in extinction was reconditioned. Test trials with other members of the class revealed that they regained elicitation function. These results demonstrate that both respondent elicitation and extinction can transfer through stimulus classes. The clinical and applied significance of the results is discussed.Key words: stimulus equivalence, transfer of function, classical conditioning, extinction, skin conductance, fear, humans Stimulus equivalence has attracted a good deal of interest recently among behavior-analytic researchers. Much of the interest stems from the contention that stimulus equivalence may provide the basis for a behavior-analytic account of symbolic behavior, language, and apparently novel behavior (e.g

The gymnotiform electric fish Brachyhypopomus pinnicaudatus communicates with a sexually dimorphic electric waveform, the electric organ discharge (EOD). Males display pronounced circadian rhythms in the amplitude and duration of their EODs. Changes in the social environment influence the magnitudes of these circadian rhythms and also produce more transient responses in the EOD waveforms. Here we show that injections of serotonin produce quick, transient, dosedependent enhancements of the male EOD characters similar to those induced by encounters with another male. The response to serotonin administered peripherally begins 5-10·min post injection and lasts approximately 3·h. The magnitude of the response to serotonin is tightly associated with the magnitude of the day-to-night swing of the circadian rhythm prior to injection. Taken together these findings suggest that the male's social environment influences his response to serotonin by altering the function of some part of the downstream chain between the serotonin receptors and the ion channels involved in control of the EOD waveform. Although chronic activation of serotonin circuitry is widely known to elicit subordinate behavior, we find that 5-HT initially increases a dominance signal in these fish. These findings are consistent with the emerging view that serotonin facilitates different adaptive responses to acute and chronic social challenge and stress.

Three experiments were conducted to investigate stimulus relations that might emerge when college students are taught relations between compound sample stimuli and unitary comparison stimuli using match-to-sample procedures. In Experiment 1, subjects were taught nine AB-C stimulus relations, then tested for the emergence of 18 AC-B and BC-A relations. All subjects showed the emergence of all tested relations. Twelve subjects participated in Experiment 2. Six subjects were taught nine AB-C relations and were then tested for symmetrical (C-AB) relations. Six subjects were taught nine AB-C and three C-D relations and were then tested for nine AB-D (transitive) relations. Five of 6 subjects demonstrated the emergence of symmetrical relations, and 6 subjects showed the emergence of transitivity. In Experiment 3, 5 college students were taught nine AB-C and three C-D relations and were then tested for nine equivalence (D-AB) relations and 18 AD-B and BD-A relations. Three subjects demonstrated all tested relations. One subject demonstrated the AD-B and BD-A relations but not the D-AB relations. One subject did not respond systematically during testing. The results of these experiments extend stimulus equivalence research to more complex cases.

We report here that melanocortin peptides appear to serve as the mechanism by which weakly electric fish couple socially regulated and stress-regulated brain pathways to unique changes in the intrinsic excitability and action potential waveform of excitable membranes in peripheral cells involved in communication. Gymnotiform electric fish modulate their electric organ discharges (EODs) by reshaping the electric discharges of excitable cells in the periphery. These fish show circadian enhancement of the EOD waveform. They also enhance their EOD waveforms within minutes in response to stressors and changes in the social environment, thus altering the communication value of the signal. Changes in the EOD waveform that occur within minutes result from changes in the discharges of individual electrocytes (EODs) mediated by the cAMP/protein kinase A (PKA) pathway acting on ion channel kinetics. What activates the cAMP/PKA pathway in electrocytes has not been identified. In vivo injections of the melanocortin peptide adrenocorticotropic hormone (ACTH) increase the amplitude and duration of the electric signal waveform of the gymnotiform Brachyhypopomus pinnicaudatus over the course of 1 h. Applied to single electrocytes in vitro, ACTH increases EOD amplitude and duration within minutes by differentially modulating the action potentials of the two excitable membranes of the electrocyte and changing the timing of these two spikes. Serotonin modulates the EOD in vivo but has no effect on the EOD in vitro. The cAMP analog 8-bromo-cAMP mimicked the effects of ACTH, whereas inhibition of PKA by protein kinase A inhibitor 14 -22 amide blocked the modulatory effects of ACTH, confirming the role of the cAMP/PKA pathway in EOD modulation by ACTH.

Weakly electric gymnotiform fish specialize in the regulation and modulation of the action potentials that make up their multi-purpose electric signals. To produce communication signals, gymnotiform fish modulate the waveforms of their electric organ discharges (EODs) over timescales spanning ten orders of magnitude within the animal's life cycle: developmental, reproductive, circadian, and behavioral. Rapid changes lasting milliseconds to seconds are the result of direct neural control of action potential firing in the electric organ. Intermediate-term changes taking minutes to hours result from the action of melanocortin peptides, the pituitary hormones that induce skin darkening and cortisol release in many vertebrates. Long-term changes in the EOD waveform taking days to weeks result from the action of sex steroids on the electrocytes in the electric organ as well as changes in the neural control structures in the brain. These long-term changes in the electric organ seem to be associated with changes in the expression of voltage-gated ion channels in two gene families. Electric organs express multiple voltage-gated sodium channel genes, at least one of which seems to be regulated by androgens. Electric organs also express multiple subunits of the shaker (Kv1) family of voltage-gated potassium channels. Expression of the Kv1 subtype has been found to vary with the duration of the waveform in the electric signal. Our increasing understanding of the mechanisms underlying precise control of electric communication signals may yield significant insights into the diversity of natural mechanisms available for modifying the performance of ion channels in excitable membranes. These mechanisms may lead to better understanding of normal function in a wide range of physiological systems and future application in treatment of disease states involving pathology of excitable membranes.