[Properties of single L-type Ca2+ channels in hypothalamic neurons of newborn rats].

AIM: To investigate the characteristics of single L-type Ca2+ channels in hypothalamic neurons. METHODS: The cell-attached patch-clamp technique and acute cell isolation technique were used. RESULTS: (1) L-type Ca2+ channels opened throughout an 768 ms long voltage pulse. (2) The averaged open-time constant was 0.28 ms(tau0), two closed-time constants were 2.91 (tau(c1)) and 53.22 ms(tau(c2)). (3) The conductance was (29.5 +/- 3.1) pS and (4) Bay K 8644 increased the open probability by prolonging the mean open time to 1.61 ms. CONCLUSION: L-type Ca2+ channel existed in hypothalamic neurons, with the similar properties to Ca2+ currents as previously reported, but showed its own peculiarity.

[Effects of Bay K8644 and nifedipine on L-type Ca2+ channels in hypothalamic neurons of rats].

To investigate the effects of Bay K8644 and nifedipine on L-type of Ca2+ channels in hypothalamic neurons, the cell-attached patch-clamp technique was used to record Ca2+ current from isolated neurons. The results showed that the averaged open time and NPo were markedly increased by Bay K8644, but had no effect on channel conductance. Nifedipine, on the contrary, had an inhibitory effect on the L-type Ca2+ channels.

Effects of dynamic range and amplitude mapping on phoneme recognition in Nucleus-22 cochlear implant users.

OBJECTIVE: To determine the consequences for phoneme recognition of errors in setting threshold and loudness levels in cochlear implant listeners using a 4-channel continuous interleaved sampling (CIS) speech processor. DESIGN: Three Nucleus-22 cochlear implant listeners, who normally used the SPEAK speech processing strategy participated in this study. An experimental 4-channel CIS speech processor was implemented in each listener as follows. Speech signals were band-pass filtered into four broad frequency bands and the temporal envelope of the signal in each band was extracted by half-wave rectification and low-pass filtering. A power function was used to convert the extracted acoustic amplitudes to electric currents. The electric currents were dependent on the exponent of the mapping power function and the electrode dynamic range, which was determined by the minimum and maximum stimulation levels. In the baseline condition, the minimum and maximum stimulation levels were defined as the psychophysically measured threshold level (T-level) and maximum comfortable level (C-level). In the experimental conditions, the maximum stimulation levels were fixed at the C-level and the dynamic range (in dB) was changed by varying the minimum stimulation levels on all electrodes. This manipulation simulates the effect of an erroneous measurement of the T-level. Phoneme recognition was obtained as the dynamic range of electrodes was changed from 1 dB to 20 dB and as the exponent of the power-law amplitude mapping function was changed from 0.1 to 0.4. RESULTS: For each mapping condition, the electric dynamic range had a significant, but weak effect on vowel and consonant recognition. For a strong compression (p = 0.1), best vowel and consonant scores were obtained with a large dynamic range (12 dB). When the exponent of the mapping function was changed to 0.2 and 0.4, the dynamic range producing the highest scores decreased to 6 dB and 3 dB, respectively. CONCLUSIONS: Phoneme recognition with a 4-channel CIS strategy was only mildly affected by large changes in both electric threshold and loudness mapping. Errors in threshold by a factor of 2 (6 dB) and in the loudness mapping exponent by a factor of 2 were required to produce a significant decrease in performance. In these extreme conditions, the effect of the electric dynamic range on phoneme recognition could be due to two independent factors: abnormal loudness growth and a reduction in the number of discriminable intensity steps. The decrease in performance caused by a reduced electric dynamic range can be compensated by a more expansive power-law mapping function, as long as the number of discriminable intensity steps is moderately large (e.g., >8).