Stretch receptor responses to sinusoidal stimuli depend critically on modulation depth and background length

Signal transduction and nonlinearities revealed by white noise inputs in the fast adapting crayfish stretch receptor

“…1A and 2A) with point modifications of sensitivities, frequency filtering properties, and nonlinearities, which may serve to enhance the detectability of the functionally relevant signal in each natural situation. The analysis verified differences, and disclosed similarities between RM2 and RM1 (Bufio et al 1983(Bufio et al , 1984(Bufio et al , 1978Diez Martinez et al 1983;Segundo et al 1985aSegundo et al , 1985b; analogies increased with prestretch and GWN amplitude. Differences between the RM1 and RM2 also deserve attention.…”

“…Both the low counts on the extreme left of the interval histograms and the trough in the atttocorrelation histograms were due to the refractory bounds present in all spike trains. Figure 2 shows that, increasing prestretch from 153 to 459gm, increased the discharge rate from 3.30 to 4.87 ips, indicating sensitivity to sustained elongation (Built et al 1983(Built et al , 1978Segundo and Diez Martinez 1985a). This sensitivity was absent when the constant length stimuli were delivered alone without GWN added to them (e.g., Fig.…”

“…Subsequent observations (Bufio et al 1983(Bufio et al , 1978 demonstrated that when perturbed by fast, small, random stretches, the RM2 shows an important qualitative modification, responding to both transients and sustained elongations, and thus becomes veritably tonic. Such changes, noted also in other phasic mechanoreceptors, imply nonlinear properties (Bufio et al 1983(Bufio et al , 1978(Bufio et al , 1981Segundo and Diez Martinez 1985a). This paper describes the consequences of subjecting the RM2 to GWN inputs of different bandwidths and amplitudes, after setting it at different lengths, or prestretches.…”

“…However, a clearcut tonic sensitivity of the encoder to sustained lengths had been demonstrated by Bufio, Fuentes and Segundo (1978) when GWN was superimposed, and the lengthfiring rate relationships were determined by Bufio, Bustamante and Fuentes (1983) and Diez Martinez, Kohn and Segundo (1983). Furthermore, sensitivity to length had been noted also with sinusoidal stimulation (Segundo and Diez Martinez 1985a).…”

“…The RM2 signal conversion is complex, thus requiring a multicomponent model. Several models have been proposed to explain its behavior, and that of its companion the RM1 (Brown and Stein 1966;Chaplain et al 1971 ;Diez Martinez et al 1983;Fohlmeister 1979;Gestrelius 1983;Houk et al 1981 ;Krnjevic and Van Gelder 1961 ;Nakajima and Onodera 1969;Poppele 1981 ;P6pel and Querfurth 1984;Segundo and Diez Martinez 1985a), as well as other mechanoreceptors (Bufio et al 1981a(Bufio et al , 1981. A complete model of the RM2 should include the following elements (in addition to those providing hysteretic, compressive and limiting nonlinearities; Segundo and Diez Martinez 1985a): (a) linear high and tow-pass filters added to provide the slowly adapting and tonic properties of the transducer (they may be due to the mechano-electrical conversion); (b) a threshold element to account for the encoder properties and rectification (i.e., the spike generator); (c) a nonlinear gain element to explain the increasing sensitivity with constant elongation (it may reside in the increased stiffness as a function of elongation (Poppele 1981), or in membrane characteristics (Barrio, Clarac and Bufio 1991;Bufio et al 1981a;P6pel and Querfurth 1984;Querfurth 1986; Barrio, Bustamante and Bufio, unpublished observations); (at) nonlinear frequency-filtering elements to explain the decrease in phasic sensitivity and the damping ratio changes with prestretch and GWN amplitude.…”