Fig. 5. Phase response curves obtained in response to 15 pmol of -aminobutyric acid (GABA), 0.15 pmol of Mas-allatotropin and control injections. Data were merged into 2 h bins. Mean ± S.E.M. transmitter-dependent phase shifts (black squares) and phase shifts following control injections (grey circles) are plotted (see Table 1 for values of N) in the middle of each 2 h bin. Asterisks indicate significant transmitter-dependent phase shifts (see values marked a in Table 1).