Influence of evoked HSP70 expression on hearing function of the cochlea in guinea pigs.

OBJECTIVE: To investigate the effect of evoked heat shock protein 70 (HSP70) expression on the hearing function of the cochlea in guinea pigs. METHODS: Guinea pigs were divided into pre-exposure group (pre-treated with white noise exposure at 100 dB SPL for 45 min) and none pre-exposure group. Auditory brainstem response (ABR) thresholds were recorded at 12, 60 and 108 h after the animals in both groups were exposed to loud white noise (125 dB SPL, 90 min). RESULTS: HSP70 expression was evoked by pre-treatment with white noise (100 dB SPL, 45 min). There was no significant difference of ABR thresholds between the 2 groups (P>0.05) at 12 h after exposure to loud noise, while ABR thresholds became lower in pre-exposure group than in none pre-exposure group (P<0.01) at both 60 and 108 h. In the pre-exposure group, ABR thresholds at 108 h were significantly lower than that measured at 60 h (P<0.05), but which was not the case in none pre-exposure group. CONCLUSION: HSP70 expression induced by pre-exposure to noise protects the hearing function of the cochlea in guinea pigs.

[Modulation of gamma-aminobutyric acid receptor on medial vestibular nucleus neurons in vivo].

OBJECTIVE: To investigate modulation of gamma-aminobutyric acid (GABA) and its receptors on medial vestibular nucleus neurons in vivo. METHODS: Twenty-six male Wistar rats were used. gamma-aminobutyric acid, bicuculline (BIC, gamma-aminobutyric acid A receptor antagonist) and 2-hydroxysaclofen (SAC, gamma-aminobutyric acid B receptor antagonist) were microiontophoresed on medial vestibular nucleus (MVN) neurons to determine the effects of gamma-aminobutyric acid and its antagonists on the neuronal firing rates of medial vestibular nucleus in rats in vivo. RESULTS: Microiontophoretic application of y-aminobutyric acid at 10, 30, 50 nA electric current produced inhibitory responses on 42 MVN neurons, these responses were dose-dependent decreases, firing rates (x +/- s) of MVN neurons decreased form (14.8 +/- 5.6) times/s to (8.7 +/- 3.4) times/s, (4.1 +/- 1.6) times/s and (2.2 +/- 1.1) times/s respectively; microiontophoretic application of bicuculline in 37 MVN neurons, 86.5% (32/37) neurons produced excitatory responses, 13.5% (5/37) neurons didn't response, firing rates of MVN neurons increased form (15.3 +/- 6.3) times/s to (16.8 +/- 7.1) times/s, (25.9 +/- 10.1) times/s and (32.7 +/- 11.3) times/s respectively at 10, 30, 50 nA electric current, which were dose-dependent increases, and the inhibitory responses of gamma-aminobutyric acid on MVN neurons were blocked by bicuculline completely; however, microiontophoretic application of 2-hydroxysaclofen didn't produced responses as bicuculline did. CONCLUSIONS: Modulation of gamma-aminobutyric acid on medial vestibular nucleus neurons was mediated by y-aminobutyric acid A receptor in vivo.