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PubMed1987

[Characteristics of the areas of synchronization of the neuronal responses of the inferior colliculi in greater horseshoe bats to the presentation of amplitude-modulated stimuli].

Response areas of synchronized discharges measured at different values of modulation rates were studied in inferior colliculus of bats (Rhinolophus ferrumequinum). Single neurons showed a variety of synchronized response areas to sinusoidally amplitude-modulated stimuli (thresholds of synchronized discharge plotted versus modulation rates, carrier frequency and modulation depth are constant). All neurons showed best modulation frequency where minimal thresholds could be obtained. Synchronized response areas measured in collicular units were sharply or widely tuned, some showed upper thresholds, tuning curves were symmetrical or asymmetrical. The data suggest that response features of studied units prove to be well suited for processing echoes produced by wing beats of flying insects.

Acoustic Stimulation↗
PubMed1981

[Ultrastructural organization of projection zones AI and AIV of the cat auditory cortex to the inferior colliculi].

By the method of anterograde degeneration, distribution of projections of functionally definite AI and AIV zones of the cat auditory cortex have been studied in the posterior calculi of the tectum opticum. It has been demonstrated electron microscopically that an essentially part of the degenerating boutons are found in the middle and caudal thirds of the colliculi, and the remaining ones terminate on the dendrites with large- and middle-size diameters and on the spines. A supposition is made that there exist two systems of the corticofugal auditory fibres. Peculiarities of the degenerative rates, specific for short- and long-axonal systems of the fibres and possible mechanisms for the influence of the auditory cortex on the neurons of the posterior colliculi of the tectum opticum are discussed.

Animals↗
PubMed1993

40-Hz steady state response in awake cats after bilateral chronic lesions in auditory cortices or inferior colliculi.

To reveal the generators of 40-Hz steady state response, the following investigations in awake cat were performed: (i) analyses of 40-Hz SSR without any lesions, and study of stimulus rate; (ii) effect of chronic lesions in the bilateral auditory cortex; (iii) effect of chronic lesions in the bilateral inferior colliculus. The maximum amplitudes were obtained at stimulus rates of 40-50 Hz. In cat with lesions in the bilateral auditory cortex, the wave configurations and the phase were retained but the amplitude was reduced to 90%. In cat with lesions in the inferior colliculus, the wave configurations and the phase were retained but the amplitude was reduced to 60%. These data suggest the following conclusions: (i) cat was a suitable animal model for human's 40-Hz SSR; (ii) the auditory cortex could be one of the generators of 40-Hz SSR; (iii) the inferior colliculus could be an important generator of 40-Hz SSR; (iv) 40-Hz SSR seems to be generated through not only primary auditory pathways, but also nonspecific auditory pathways, which receive auditory information in parallel from the brainstem, thalamus, and cerebrum.

Animals↗
PubMed1997

Fos-immunoreactive responses in inferior colliculi of rats with experimental audiogenic seizure susceptibility.

Audiogenic seizure (AGS) susceptibility is a reflex epilepsy of rodents in which acoustic stimulation evokes wild running attacks and subsequent convulsions. Susceptibility can be induced in non-susceptible strains by treatments causing transient or permanent hearing losses as long as these occur during the neonatal period. The defect which is the basis of susceptibility has been proposed to be a failure of developmental organization of inferior colliculus (IC) into frequency selective zones. That is, high frequency stimuli evoke responses in broader arrays of neurons in ICs of susceptible rats than in those of neonatally untreated (non-susceptible) controls. Nonetheless, this observation has been made only in rats in which susceptibility was induced by exposure to intense noise on postnatal day (PND) 14. By contrast, the present study examines whether unusually broad topographic responses are also characteristic in ICs of rats made susceptible by the neonatal administration of low doses of the ototoxic antibiotic, kanamycin (KM). Patterns of Fos-like immunoreactivity (Foslir) induced by seizures or pure tone stimuli were compared in ICs of adult Wistar rats which neonatally had been (a) sham-treated; (b) noise-exposed on PND 14; or (c) injected on PNDs 9-12 with 100 mg/kg KM. It was found that sound-triggered seizures in the two experimental groups resulted in induction of Foslir primarily within cortical areas of IC. By contrast, pure tones evoked unusually broad responses in the central nucleus of ICs of both susceptible groups but not in those of controls. Additionally, in the KM-treated rats, the range of frequencies evoking abnormal responses extended one octave lower than was characteristic of noise-exposed rats. The earlier schedule of treatments in the KM model may account for this inasmuch as low frequency response domains undergo development at younger ages. The similarity of results in the two models suggests failure of development of frequency selective fields in IC is indeed the common basis of experimentally induced susceptibility to sound-triggered seizures.

Acoustic Stimulation↗
PubMedDate not supplied

[Effect of sectioning the brachia of the inferior colliculi on the formation of auditory conditioned reflexes to amplitude-modulated stimuli].

Elaboration of differentiation of tonal and amplitude-modulated stimuli with a frequency modulation of 5 Hz conducted on laboratory rats in five months after section of brachii colliculi proved to be impossible. The rate of correct reactions did not differ from the probability of random choice during 500 presentations of conditioned stimuli but significantly differed from the values obtained during differentiation of these signals in rats after control operation. Electrophysiological control showed that while in the control group and in intact animals at the presentation of amplitude-modulated stimuli with modulation frequency of 1-20 Hz summary potentials were recorded in the auditory cortex synchronized with their modulation frequency,--in rats after section of brachii colliculi only on- and off-responses were observed. It may be suggested that sensory providing of conditioned activity during the action of amplitude-modulated stimuli with low modulation frequency may be achieved only with the participation of specific pathways.

Acoustic Stimulation↗
PubMedDate not supplied

[Role of the inferior colliculi in the formation of conditioned reflexes to amplitude-modulated stimuli in rats].

After a bilateral ablation of the rat auditory cortex, differentiation of a tonal signal from an amplitude-modulated stimulus with 50 c/s modulation frequency is preserved, while ablation of the posterior colliculi completely abolishes differentiation of these signals, without subsequent restoration in six months after the operation. At the same time the same rats are able to elaborate a differentiation of a tonal signal from an amplitude-modulated signal with a 500 c/s modulation frequency. The results obtained show that the posterior colliculi are at the level of the auditory system, where the coding of signals with a modulation frequency of 50 c/s amplitude is accomplished, whereas stimuli with a higher frequency of amplitude modulation are coded at a lower level of the auditory system.

Animals↗
PubMed1985

[Overall synchronized response of the inferior colliculi to lateralization of complex sounds].

Interaural differences in time, intensity or phase introduced into a different frequency component of complex sounds results in changes of amplitude and form of the frequency following response depending on the frequency and phase ranges of the sounds. This relationship may be due to physical differences in stimulation of both ears, i. e. to differences in the sound wave forms and, consequently, in conditions of the convergence of both monaural afferent inflows.

Animals↗
PubMedDate not supplied

[The role of the temporal areas in conditioned reflex activity following section of the brachia of the inferior colliculi].

The role of the neocortex temporal areas in the closing function was studied in chronic experiments on cats in the norm and after section of the posterior colliculi brachia. The techniques of functional elimination of the temporal neocortex by cold and section of the posterior colliculi brachia were used. Functional elimination of the cortical temporal areas prevents formation of a stable conditioned reflex in the first twenty sessions with cooling. Conditioned reflexes elaborated after section of the posterior colliculi brachia are not manifested in the case of cooling of the temporal areas throughout the period of observation (18 sessions). At the same time the conditioned reflexes elaborated before the section, are restored quite rapidly (five to six sessions). Hence, the neocortex temporal areas are more important for setting up conditioned connections than for their preservation and the use of connections previously elaborated.

Animals↗
PubMedDate not supplied

Tonic organization of the inferior colliculi in the cat in conditions of simulated sound source motion.

Simulation of the motion of a sound source using a series of clicks with variable interaural delays was used to study movement effects as changes in the amplitude of sequential focal evoked potentials (EP) in series of EP arising in response to the signal. These experiments showed that a) in 25% of cases the movement effect depended on the direction of the simulated motion; b) the movement effect was better represented on the wide ipsilateral to the site of EP recording; left- and right-sided movement effects were identically dependent on the rate of motion; c) the phenomenon of the movement effect was associated with the dominance of contralateral afferentation compared with ipsilateral afferentation; d) the movement effect was accompanied by inhibitory manifestations consisting of suppression of monaural afferentation in conditions of binaural stimulation; e) marked movement effects were seen mainly in the ventrocentral part of the central nucleus, located very close to the positions of large multipolar neurons, while mild and moderate movement effects were distributed quite uniformly though the volume of the nucleus, following the distribution of the "basic" neurons; it is suggested that movement effects of different strengths are associated with differences in the ratios of the effectivenesses of ipsi- and contralateral stimulation, which depend on the properties of multipolar and "basic" neurons in the central nucleus of the inferior colliculus in relation to their responses to ipsi- and contralateral stimulation.

Acoustic Stimulation↗
PubMed2005

A three-dimensional digital atlas database of the adult C57BL/6J mouse brain by magnetic resonance microscopy.

A comprehensive three-dimensional digital atlas database of the C57BL/6J mouse brain was developed based on magnetic resonance microscopy images acquired on a 17.6-T superconducting magnet. By using both manual tracing and an atlas-based semi-automatic segmentation approach, T2-weighted magnetic resonance microscopy images of 10 adult male formalin-fixed, excised C57BL/6J mouse brains were segmented into 20 anatomical structures. These structures included the neocortex, hippocampus, amygdala, olfactory bulbs, basal forebrain and septum, caudate-putamen, globus pallidus, thalamus, hypothalamus, central gray, superior colliculi, inferior colliculi, the rest of midbrain, cerebellum, brainstem, corpus callosum/external capsule, internal capsule, anterior commissure, fimbria, and ventricles. The segmentation data were formatted and stored into a database containing three different atlas types: 10 single-specimen brain atlases, an average brain atlas and a probabilistic atlas. Additionally, quantitative group information, such as variations in structural volume, surface area, magnetic resonance microscopy image intensity and local geometry, were computed and stored as an integral part of the database. The database augments ongoing efforts with other high priority strains as defined by the Mouse Phenome Database focused on providing a quantitative framework for accurate mapping of functional, genetic and protein expression patterns acquired by a myriad of technologies and imaging modalities.

Anatomy, Artistic↗
PubMed1987

Diurnal variation of cation pump enzyme activity in pineal and seven other rat brain regions.

Adult female Long-Evans rats were maintained on an automatically regulated artificial lighting schedule of light:dark (L:D) 14.5:9.5 for 12 wk. After sacrifice at 0630, 1130, 1600, 1800, 2000, 2200, 0230, or 0400, the pineals were removed, weighed, and assayed for N-acetyltransferase (NAT), melatonin, Mg++-paranitrophenylphosphatase (pNPPase), and K-pNPPase activity. The brains were quickly dissected into the following areas: cerebellum, superior colliculi, inferior colliculi, visual cortex, auditory cortex, sensorimotor cortex, and the hypothalamic area around the suprachiasmatic nucleus. These regions were weighed and 10% sucrose homogenates were prepared for determinations of protein, Mg++-pNPPase, and K+-pNPPase activity. Pineal melatonin rose over six-fold from 144 +/- 70 pg/gland at 1130 to 981 +/- 173 pg/gland at 0230. Similarly, pineal NAT activity rose over 11-fold, from 119 +/- 12 pmol/gland/h to 1315 +/- 232 pmol/gland/h at the same times. K+-pNPPase activity rose by about two-thirds, from 133 +/- 12.8 nmol/gland/h to 224 +/- 22.3 nmol/gland/h from 1600 to 0230. However, when expressed per mg protein, these differences in pNPPase activity were not significant. There were no significant daily rhythms discernible in any of the seven other brain regions across these times. We conclude that cation pump enzyme activity varies only slightly with time in the rat brain and pineal gland, in spite of definite daily rhythms of pineal melatonin and NAT activity.

4-Nitrophenylphosphatase↗
PubMed1988

Differentiation between brain lesions in experimental thiamine deficiency.

Dietary deprivation of thiamine combined with pyrithiamine administration in rats was used for pathophysiological and morphological investigations. The animals passed through three different symptomatic stages, ranging from slight neurological abnormalities to generalized seizures from day 8 up to day 11. Hypothermia was a consistent finding during the second week. Histological examination revealed two types of neuropathological lesions in the rats. Those in the colliculi inferiores and the vestibular nuclei were characterized by a bullous spongiform appearance of the neuropil with severely damaged, pale and oedematous nerve cells. Alterations in the thalamus and inferior olives, however, showed eosinophilic nerve cell necrosis of the ischemic type which resembles the thalamic pathology found in human cases of Wernicke's encephalopathy.

Animals↗