Theophylline-induced changes in the mouse brainstem auditory evoked potential

Auditory brainstem responses are resistant to pharmacological modulation in Sprague Dawley wild-type and Neurexin1α knockout rats

Sensory processing in the auditory brainstem can be studied with auditory brainstem responses (ABRs) across species. There is, however, a limited understanding of ABRs as tools to assess the effect of pharmacological interventions. Therefore, we set out to understand how pharmacological agents that target key transmitter systems of the auditory brainstem circuitry affect ABRs in rats. Given previous studies, demonstrating that Nrxn1α KO Sprague Dawley rats show substantial auditory processing deficits and altered sensitivity to GABAergic modulators, we used both Nrxn1α KO and wild-type littermates in our study. First, we probed how different commonly used anesthetics (isoflurane, ketamine/xylazine, medetomidine) affect ABRs. In the next step, we assessed the effects of different pharmacological compounds (diazepam, gaboxadol, retigabine, nicotine, baclofen, and bitopertin) either under isoflurane or medetomidine anesthesia. We found that under our experimental conditions, ABRs are largely unaffected by diverse pharmacological modulation. Significant modulation was observed with (i) nicotine, affecting the late ABRs components at 90 dB stimulus intensity under isoflurane anesthesia in both genotypes and (ii) retigabine, showing a slight decrease in late ABRs deflections at 80 dB stimulus intensity, mainly in isoflurane anesthetized Nrxn1α KO rats. Our study suggests that ABRs in anesthetized rats are resistant to a wide range of pharmacological modulators, which has important implications for the applicability of ABRs to study auditory brainstem physiology.

Brainstem auditory evoked potentials characteristics in mice: the effect of genotype

Brainstem auditory evoked potentials (BAEPs) elicited by sound clicks were recorded as a function of stimulus intensity in pentobarbital anesthetized C57BL/6J and BALB/c male mice, 2.5 months old. At high stimulus intensities the BAEPs of both strains consisted of 4 positive and 4 negative waves (labelled P1-P4 and N1-N4, correspondingly). However, great interstrain differences were observed. BALB/c mice were characterized by higher thresholds, less amplitudes, beginning with P1 peak, longer latencies and steeper in slope latency-intensity profiles. The data suppose that by this age C57BL/6J mice have better auditory acuity, than BALB/c, and in BALB/c mice the pronounced abnormalities appear to arise in cochlear-auditory nerve system. Analysis of BAEPs using interpeak latencies (IPLs) and amplitude ratios intensities (ARs) profiles technique demonstrated no general trend that could fit for all IPLs as well as for all Ars changes by varying stimulus intensity. The obtained interstrain and interpeak differences in BAEPs parameters suggest that auditory information processing may vary greatly as a function of brainstem level.

Effects of cocaine on the brain-stem auditory evoked potential in the Long-Evans rat

The present study examined the effects of an acute psychoactive dose of cocaine hydrochloride (HCl) in the rat, using the brain-stem auditory evoked potential (BAEP) as an objective, quantitative measure of this substance's effects on brain and auditory electrophysiology. The animals were 8 adult Long-Evans rats (4 female, 4 male). BAEPs were recorded from skull screw electrodes during a baseline period as well as 30-90 min after cocaine HCl treatment (10 mg/kg, i.p.). Normothermia was maintained to control for possible temperature-related effects. Cocaine's effects on the BAEP were examined over a broad range of stimulus intensities (intensity profiles) and repetition rates (rate profiles). Cocaine prolonged latencies of several BAEP components at low stimulus intensities and shortened these latencies at high stimulus intensities. The average BAEP threshold was also increased by cocaine treatment. These results were not strong, but were suggestive of a recruitment type change in auditory function. Cocaine treatment had no convincing effects on the BAEP as a function of stimulus repetition rate.

Dose-dependent effects of atropine sulfate on the brainstem and cortical auditory evoked potentials in the rat

Because brainstem auditory evoked potentials (BAEPs) are frequently recorded in anesthetized animals and humans, it is important to become familiar with the effects on the BAEP of drugs used during anesthesia, including pre-anesthetics. The dose-dependent and stimulus intensity-dependent effects on the BAEP of a pre-anesthetic, atropine sulfate, were studied in the unanesthetized rat. The animal subjects were 11 adult female Long-Evans rats. BAEPs in response to 0.1 ms clicks (12.5/s) were recorded from skull screw electrodes during a baseline period, as well as after saline and atropine treatments. Atropine sulfate was given i.p. in doses ranging from 0.250 to 40 mg/kg. Contrary to a prior report, doses in the standard pre-anesthetic range (i.e. 0.250-1.000 mg/kg) did not convincingly influence the BAEP. Only the highest dose (40 mg/kg) produced a significant and noteworthy change in the BAEP. This effect was characterized by significant amplitude increases in the P1, P2 and P3 components, but not in the P4, P5 and P6 components. This selective effect occurred at the highest stimulus intensity of 110 dB peak equivalent sound pressure level, but not at lower intensities. There were no convincing atropine-induced changes in BAEP latencies. Atropine-induced changes in the cortical auditory evoked potential (CAEP) were characterized by amplitude decrements. Thus, atropine seemed to have an excitatory effect on the BAEP and an inhibitory or depressive effect on the CAEP.

Effects of ketamine anesthesia on the rat brain-stem auditory evoked potential as a function of dose and stimulus intensity

Because ketamine is both an abused substance and a commonly used veterinary anesthetic, its effects on brain and sensory functions are of interest. The present study examined the dose-dependent effects of ketamine anesthesia in the rat, using the brain-stem auditory evoked potential (BAEP) as an objective, quantitative measure of this substance's acute effects on brain and sensory electrophysiology. The animal subjects were 11 young adult female Long-Evans rats. BAEPs were recorded from skull screw electrodes during a baseline period as well as after saline and ketamine treatments. Ketamine was administered (i.p.) in 2 serial doses. The first dose (100 mg/kg) was followed 30-40 min later by a second dose (also 100 mg/kg). Equal volumes of normal saline were also injected serially. An interval of 1-2 weeks occurred between the saline and ketamine treatments, with treatment order counterbalanced. Normothermia was maintained to control for possible temperature-related effects. Ketamine produced prolongations in the latencies of all BAEP components (P1 through P6) that were statistically significant relative to baseline values. These latency shifts were progressively greater for waves P1 through P4 (shifts in P5 and P6 approximated the P4 shift). The effect of the second ketamine injection was to nearly double the latency shifts. Ketamine also had significant and complex effects on BAEP amplitudes that were dependent on dose and stimulus intensity. The results of the present study challenge the belief that the BAEP is resistant to the effects of anesthetics and suggest that the BAEP is useful in characterizing the CNS and sensory effects of these pharmacological agents.