J. Astl et al., COMPARISON OF RESPONSE PROPERTIES OF NEURONS IN THE INFERIOR COLLICULUS OF GUINEA-PIGS UNDER DIFFERENT ANESTHETICS, Audiology, 35(6), 1996, pp. 335-345
Responses of the inferior colliculus (IC) neurons to acoustical stimul
ation were recorded in anesthetized guinea pigs Three kinds of anesthe
sia were used: (1) urethane (8 ml/kg b.w of 20 per cent solution i.p.)
; (2) ketamine-xylazine combination (1 ml/kg b.w of mixture 2:1); and
(3) pentobarbital (25 mg/kg i.p.) combined with intramuscular injectio
n of fentanyl (0.5 mi) and droperidol (1 mi). The frequency tuning of
neurons evaluated on the basis of Q(10) values and the composite neura
l audiogram represented by points of lowest thresholds of individual I
C neurons were similar for guinea pigs treated with any of the anesthe
tics. The number of spontaneously active IC neurons was significantly
larger with ketamine than with urethane or pentobarbital. The response
latencies to tone bursts at characteristic frequency (CF) were shorte
st in animals anesthetized with pentobarbital. Whereas with ketamine a
nd urethane many neurons were recorded in which response latencies wer
e longer than 40 ms, in pentobarbital-anesthetized animals the latenci
es usually did not exceed 25 ms. The occurrence of neurons with an ons
et type of response was significantly larger with pentobarbital than w
ith the other two anesthetics. In ketamine and urethane anesthesia, th
resholds of units with sustained response were significantly lower tha
n thresholds of units with onset response. Our results suggest that in
experiments where the level of spontaneous activity, latency and type
of responses are important parameters, the kind of anesthesia should
be taken into account.