Psychoacoustic tests: effects of atropine]

The efferent pathways exert a control action on the function of the cochlear nucleus and hair cells. Acetylcholine is the neurotransmitter of the centrifugal system and its action can be blocked by atropine. In order to give a contribution to the knowledge of the function of the efferent bundle and of the cochlea efficiency we examined 10 young normal subjects before and after infusion of 1 mg of atropine i.v. a battery of three psychoacoustical tests (Remote Masking, Critical Ratio and Brief Tone Audiometry). After infusion of atropine we have shown an increase of 0.25 Hz hearing threshold, an increase of RC values and a decrease of RM values. It can be concluded that the pharmacological block of the olivo-cochlear bundle determines a stiffness of outer hair cells and basilar membrane; this finding means that the atropine can inhibit the facilitating activity of the efferent system on the cochlear performance.     

Brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 10 common marmosets (Callithrix jacchus) to investigate the effects of recording electrode configurations, stimulus rate, and stimulus frequency on BAEP wave forms and peak latencies. Tone burst stimulations were used to evaluate the effects of pure tone on BAEP wave forms. Five positive peaks superimposed on positive and negative slow potentials were identified in the BAEP recorded at the linkage between the vertex and the dorsal base of the ear ipsilateral to a monaural stimulus. When the reference electrode was placed at the ipsilateral mastoid or the neck, the amplitudes of positive and negative slow potentials and the incidence of wave I increased. There were no significant changes in peak latencies of BAEP waves with changes in stimulus rate from 5 to 20/s. It was possible to record the BAEPs in response to tone burst stimulations at frequencies extending from 0.5 to 99 kHz. Wave I appeared apparently at high stimulus frequencies; while waves III to V, at low frequencies. Wave II was recorded at frequencies ranging from 0.5 to 99 kHz and comprised a superposition of 2 or 3 potentials.     

Brain-stem evoked potentials and noise effects in seagulls

Brain-stem auditory evoked potentials (BAEP) recorded from the seagull were large-amplitude, short-latency, vertex-positive deflections which originate in the eighth nerve and several brain-stem nuclei. BAEP waveforms were similar in latency and configurations to that reported for certain other lower vertebrates and some mammals. BAEP recorded at several pure tone frequencies throughout the seagull's auditory spectrum showed an area of heightened auditory sensitivity between 1 and 3 kHz. This range was also found to be the primary bandwidth of the vocalization output of young seagulls. Masking by white noise and pure tones had remarkable effects on several parameters of the BAEP. In general, the tone- and click-induced BAEP were either reduced or obliterated by both pure tone and white noise maskers of specific signal to noise ratios and high intensity levels. The masking effects observed in this study may be related to the manner in which seagulls respond to intense environmental noise. One possible conclusion is that intense environmental noise, such as aircraft engine noise, may severely alter the seagull's localization apparatus and induce sonogenic stress, both of which could cause collisions with low-flying aircraft.     

Evoked acoustic oto-emissions: effects of atropine

The Evoked Otoacoustic Emissions (EOE) are a sinusoidal wave complex coming from the contractile properties of the cochlea and particularly of the outer hair cells. This activity is influenced by the centrifugal pathways whose transmitter is acetylcholine. In order to study the effects of the functional block of the cochlea, ten young normal subjects were examined recording the EOE before and ten mins after the i.v. infusion of 1 mg of atropine. The statistical analysis of the results has shown a significant decrease only in EOE appearance threshold in absence of modifications of the saturation level. These data have led us to believe that atropine blocking of the centrifugal pathways causes a disfunction of the outer hair cells that accept less energy to be transduced into a neural stimulus and on the other hand more energy as EOEs.     

Evoked potentials and electric resistance of the cerebral cortex under the effects of strychnine and atropine]

The effect of strychnine and atropine on the amplitude of the evoked potentials (EP) of the cerebral cortex was studied. It was shown, that both drugs increased amplitude of the EP. When we used strychnine, increased amplitude of the EP determined modification of the electrical resistance and current sources of the electrical field of the EP. Atropine did not change electrical resistance and in this case only electrical current sources determined modification of the EP.     

Brain-stem listeriosis: a comparison of SPECT and MRI findings

Listeria monocytogenes, although uncommon as a cause of illness in the general population, can result in serious illness when it affects pregnant women, neonates, the elderly, and immunocompromised individuals. Typically, it is a food-borne organism. This report describes a case of brain-stem listeriosis in a previously healthy 51-year-old woman. The diagnosis was based on clinical findings, the results of cerebrospinal fluid (CSF) analysis, CSF culture, and magnetic resonance imaging (MRI) findings. MRI demonstrated upper brain stem and cerebellar peduncle involvement. In addition, Tc-99m exametazime (HMPAO)-labeled single photon emission computed tomography (SPECT) of the brain revealed bilateral cerebellar hypoperfusion. Antibiotic therapy resulted in partial clinical recovery after 3 weeks. At the end of 6 months, brain-stem findings had nearly resolved. However, although minimal residual findings were observed on MRI at 6 months, bilateral diffuse cerebellar hypoperfusion remained on Tc-99m HMPAO brain SPECT.     

Diameters and conduction velocities of fibers in the cat auditory pathways

The diameters of nerve fibers in the brachium colliculi inferioris and geniculo-cortical tract were measured. The thickness of these fibers ranges from 0.5 to 6.0 µ, and in 82–88% of them it is 1.0–3.0 µ. About 100,000 nerve fibers were found in cross-sections through the brachium colliculi inferioris. The velocity of conduction along centripetal fibers of the geniculo-cortical tract was determined. It varied from 11 to 28.6 m/sec in different fibers, and in 71% of them it was between 15 and 22 m/sec. The composition of the fibers of the geniculo-cortical tract was compared relative to their thickness and conduction velocity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 608–611, November–December, 1972.     

Carbamates, atropine, and diazepam: effects on performance in the running rat

We have reported that when rats (500 g, male) are exercised to exhaustion on a treadmill, pretreatment with the centrally acting carbamate physostigmine reduced endurance (run time, RT) and increased the rate of rise of core temperature (Tc+). Both RT and Tc+ were restored to control levels by pretreatment with either or a combination of atropine (A), and diazepam (D). Our objective in the present work was to determine whether A+D could also restore the performance and thermoregulatory decrements induced by the peripherally acting carbamate pyridostigmine (PY). After drug administration, rats were run (11 m/min, 6 degrees elevation, Ta = 26 degrees C) to exhaustion. PY treatment resulted in a reduced RT and an increased heat gain that neither A nor D alone (A+PY and D+PY) could restore to control levels. On the other hand, a combination of both A and D restored these variables to control levels. In conclusion, A+D can restore the performance and thermoregulatory decrements resulting from the administration of either a centrally or a peripherally acting carbamate.     

Inhibitory effects of atropine on serum prolactin levels after TRH stimulation

The authors have tested serum levels of PRL after administration of atropine 10' and 60' before stimulation test with TRH, in 12 male and 12 female. The administration of the drug 10' before TRH has inhibited the PRL release, in all the groups. No effect presented atropine if administered 60' before TRH test.