(1/6631) Effect of morphine and naloxone on priming-induced audiogenic seizures in BALB/c mice.

1 Morphine (1-200 mg/kg s.c.) reduced the incidence and prolonged the latency of priming-induced audiogenic siezures in a dose-dependent manner. 2 This effect was reversed by naloxone (1 and 2 mg/kg) although naloxone was itself inactive. 3 This priming-induces seizure model may be useful in the study of tolerance and physical dependence.  (+info)

(2/6631) The functional anatomy of the normal human auditory system: responses to 0.5 and 4.0 kHz tones at varied intensities.

Most functional imaging studies of the auditory system have employed complex stimuli. We used positron emission tomography to map neural responses to 0.5 and 4.0 kHz sine-wave tones presented to the right ear at 30, 50, 70 and 90 dB HL and found activation in a complex neural network of elements traditionally associated with the auditory system as well as non-traditional sites such as the posterior cingulate cortex. Cingulate activity was maximal at low stimulus intensities, suggesting that it may function as a gain control center. In the right temporal lobe, the location of the maximal response varied with the intensity, but not with the frequency of the stimuli. In the left temporal lobe, there was evidence for tonotopic organization: a site lateral to the left primary auditory cortex was activated equally by both tones while a second site in primary auditory cortex was more responsive to the higher frequency. Infratentorial activations were contralateral to the stimulated ear and included the lateral cerebellum, the lateral pontine tegmentum, the midbrain and the medial geniculate. Contrary to predictions based on cochlear membrane mechanics, at each intensity, 4.0 kHz stimuli were more potent activators of the brain than the 0.5 kHz stimuli.  (+info)

(3/6631) The effects of d-amphetamine on the temporal control of operant responding in rats during a preshock stimulus.

The operant behavior of six rats was maintained by a random-interval schedule of reinforcement. Three-minute periods of noise were superimposed on this behavior, each period ending with the delivery of an unavoidable shock. Overall rates of responding were generally lower during the periods of noise than in its absence (conditioned suppression). These suppressed response rates also exhibited temporal patterning, with responding becoming less frequent as each noise period progressed. The effects of d-amphetamine on this behavioral baseline were then assessed. In four animals the relative response rates during the noise and in its absence suggested that the drug produced a dose-related decrease in the amount of conditioned suppression. However, this effect was often due to a decrease in the rates of responding in the absence of the preshock stimulus, rather than to an increase in response rates during the stimulus. Temporal patterning in response rates during the preshock stimulus was abolished, an effect that was interpreted in terms of rate-dependent effect of d-amphetamine. This study thus extends rate-dependent analyses of the effects of amphetamines to the patterns of operant behavior that occur during a preshock stimulus, and which have been discussed in terms of the disrupting effects of anxiety on operant behavior.  (+info)

(4/6631) Midbrain combinatorial code for temporal and spectral information in concurrent acoustic signals.

All vocal species, including humans, often encounter simultaneous (concurrent) vocal signals from conspecifics. To segregate concurrent signals, the auditory system must extract information regarding the individual signals from their summed waveforms. During the breeding season, nesting male midshipman fish (Porichthys notatus) congregate in localized regions of the intertidal zone and produce long-duration (>1 min), multi-harmonic signals ("hums") during courtship of females. The hums of neighboring males often overlap, resulting in acoustic beats with amplitude and phase modulations at the difference frequencies (dFs) between their fundamental frequencies (F0s) and harmonic components. Behavioral studies also show that midshipman can localize a single hum-like tone when presented with a choice between two concurrent tones that originate from separate speakers. A previous study of the neural mechanisms underlying the segregation of concurrent signals demonstrated that midbrain neurons temporally encode a beat's dF through spike synchronization; however, spectral information about at least one of the beat's components is also required for signal segregation. Here we examine the encoding of spectral differences in beat signals by midbrain neurons. The results show that, although the spike rate responses of many neurons are sensitive to the spectral composition of a beat, virtually all midbrain units can encode information about differences in the spectral composition of beat stimuli via their interspike intervals (ISIs) with an equal distribution of ISI spectral sensitivity across the behaviorally relevant dFs. Together, temporal encoding in the midbrain of dF information through spike synchronization and of spectral information through ISI could permit the segregation of concurrent vocal signals.  (+info)

(5/6631) Desynchronizing responses to correlated noise: A mechanism for binaural masking level differences at the inferior colliculus.

We examined the adequacy of decorrelation of the responses to dichotic noise as an explanation for the binaural masking level difference (BMLD). The responses of 48 low-frequency neurons in the inferior colliculus of anesthetized guinea pigs were recorded to binaurally presented noise with various degrees of interaural correlation and to interaurally correlated noise in the presence of 500-Hz tones in either zero or pi interaural phase. In response to fully correlated noise, neurons' responses were modulated with interaural delay, showing quasiperiodic noise delay functions (NDFs) with a central peak and side peaks, separated by intervals roughly equivalent to the period of the neuron's best frequency. For noise with zero interaural correlation (independent noises presented to each ear), neurons were insensitive to the interaural delay. Their NDFs were unmodulated, with the majority showing a level of activity approximately equal to the mean of the peaks and troughs of the NDF obtained with fully correlated noise. Partial decorrelation of the noise resulted in NDFs that were, in general, intermediate between the fully correlated and fully decorrelated noise. Presenting 500-Hz tones simultaneously with fully correlated noise also had the effect of demodulating the NDFs. In the case of tones with zero interaural phase, this demodulation appeared to be a saturation process, raising the discharge at all noise delays to that at the largest peak in the NDF. In the majority of neurons, presenting the tones in pi phase had a similar effect on the NDFs to decorrelating the noise; the response was demodulated toward the mean of the peaks and troughs of the NDF. Thus the effect of added tones on the responses of delay-sensitive inferior colliculus neurons to noise could be accounted for by a desynchronizing effect. This result is entirely consistent with cross-correlation models of the BMLD. However, in some neurons, the effects of an added tone on the NDF appeared more extreme than the effect of decorrelating the noise, suggesting the possibility of additional inhibitory influences.  (+info)

(6/6631) Corticofugal amplification of facilitative auditory responses of subcortical combination-sensitive neurons in the mustached bat.

Recent studies on the bat's auditory system indicate that the corticofugal system mediates a highly focused positive feedback to physiologically "matched" subcortical neurons, and widespread lateral inhibition to physiologically "unmatched" subcortical neurons, to adjust and improve information processing. These findings have solved the controversy in physiological data, accumulated since 1962, of corticofugal effects on subcortical auditory neurons: inhibitory, excitatory, or both (an inhibitory effect is much more frequent than an excitatory effect). In the mustached bat, Pteronotus parnellii parnellii, the inferior colliculus, medial geniculate body, and auditory cortex each have "FM-FM" neurons, which are "combination-sensitive" and are tuned to specific time delays (echo delays) of echo FM components from the FM components of an emitted biosonar pulse. FM-FM neurons are more complex in response properties than cortical neurons which primarily respond to single tones. In the present study, we found that inactivation of the entire FM-FM area in the cortex, including neurons both physiologically matched and unmatched with subcortical FM-FM neurons, on the average reduced the facilitative responses to paired FM sounds by 82% for thalamic FM-FM neurons and by 66% for collicular FM-FM neurons. The corticofugal influence on the facilitative responses of subcortical combination-sensitive neurons is much larger than that on the excitatory responses of subcortical neurons primarily responding to single tones. Therefore we propose the hypothesis that, in general, the processing of complex sounds by combination-sensitive neurons more heavily depends on the corticofugal system than that by single-tone sensitive neurons.  (+info)

(7/6631) Effects of chronic administration of kanamycin on conditioned suppression to auditory stimulus in rats.

The conditioned suppression technique was employed to study the ototoxic effects of chronic administration of the antibiotic, kanamycin. Lever pressing behavior for food reinforcement of rats was suppressed in the presence of an auditory stimulus (sound) or visual stimulus (light) that had been previously paired with electric shocks. Repeated administration of kanamycin at the dose of 400 mg/kg/day for more than 50 days significantly attenuated the conditioned suppression to auditory stimulus but did not attenuate the conditioned suppression to visual stimulus. This finding suggests that the attenuating effect of chronic administration of kanamycin on conditioned suppression to auditory stimulus can be interpreted in terms of the selective action of the drug on the auditory system.  (+info)

(8/6631) Blockade of N-methyl-D-aspartate receptor activation suppresses learning-induced synaptic elimination.

Auditory filial imprinting in the domestic chicken is accompanied by a dramatic loss of spine synapses in two higher associative forebrain areas, the mediorostral neostriatum/hyperstriatum ventrale (MNH) and the dorsocaudal neostriatum (Ndc). The cellular mechanisms that underlie this learning-induced synaptic reorganization are unclear. We found that local pharmacological blockade of N-methyl-D-aspartate (NMDA) receptors in the MNH, a manipulation that has been shown previously to impair auditory imprinting, suppresses the learning-induced spine reduction in this region. Chicks treated with the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid (APV) during the behavioral training for imprinting (postnatal day 0-2) displayed similar spine frequencies at postnatal day 7 as naive control animals, which, in both groups, were significantly higher than in imprinted animals. Because the average dendritic length did not differ between the experimental groups, the reduced spine frequency can be interpreted as a reduction of the total number of spine synapses per neuron. In the Ndc, which is reciprocally connected with the MNH and not directly influenced by the injected drug, learning-induced spine elimination was partly suppressed. Spine frequencies of the APV-treated, behaviorally trained but nonimprinted animals were higher than in the imprinted animals but lower than in the naive animals. These results provide evidence that NMDA receptor activation is required for the learning-induced selective reduction of spine synapses, which may serve as a mechanism of information storage specific for juvenile emotional learning events.  (+info)