Biomedical subjects
Publications and source records attributed to R R Capranica.
The phenomenon of two-tone suppression was studied quantitatively in the peripheral auditory system of the green treefrog (Hyla cinerea). Linear relationships were found between best excitatory and best suppressor frequency, between response thresholds at these frequencies, between Q 10dB-values of excitatory and suppressor tuning curves and best excitatory frequency, and between both Q 10dB-values.
Single fibers in eight nerve of anurans exhibit varying rates of short-term adaptation in response to long duration tonal stimuli. In this report, we show that the response of an anuran auditory nerve fiber to a short probe tone presented 10-1000 ms after a long duration adapting tone depends on the fiber's state of adaptation due to previous stimulation. These effects are most pronounced in fibers presumably originating from the amphibian papilla. Within this group of fibers, fast-adapting fibers, which are most sensitive to mid-frequency tones, showed greater response decrement than did slow-adapting fibers, which are most sensitive to low-frequency tones. Fibers tuned to higher frequency ranges, which presumably originate from the basilar papilla, showed response decrements similar to those shown by slow-adapting fibers from the amphibian papilla. These results indicate that anuran auditory nerve fibers, unlike mammalian auditory nerve fibers, are not homogeneous in their sensitivities to the effects of prior stimulation.
Binaural cells in the superior olive normally have identical frequency sensitiveness when acoustically stimulated via either ear. The precision with which central connections are reformed after auditory nerve regeneration can be determined by comparing the frequency sensitiveness of the two binaural inputs to these cells. Three months after cutting the nerve and subsequent regeneration in the leopard frog, binaural cells once again have well-matched frequency sensitivities. Thus, the specificity of central connectivity that characterizes the auditory system in normal animals is restored after regeneration.
The ability of auditory fibers in the anuran's VIIIth nerve to regenerate back into the central nervous system after their axons have been served was studied electrophysiologically and anatomically. Single unit recordings in the regenerated portion of the nerve indicate that: (1) fibers from both the amphibian and basilar papillae regenerate; (2) tuning curves of regenerated fibers, as in normal fibers, are 'V' shaped and retain their sharp frequency selectivity; (3) latency and threshold measurements of regenerated fibers are similar to values obtained in intact nerves. Filling the posterior branch of the regenerated VIIIth nerve with horseradish peroxidase indicates that fibers in this branch remain together within the nerve during regeneration and succeed in terminating in their correct target nuclei and no others.
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Two auditory responsive regions in the telencephalon of the bullfrog were localized by combining systematic evoked potential depth recordings with subsequent histological studies. Large negative potentials (n1) from the ventral striatum and large positive potentials (p1) from the medial pallium were recorded in response to complex sounds with parameters similar to those found in the species-specific vocalizations. Simple acoustic stimuli, such as clicks and single tones, failed to excite these regions. Although the source of the auditory afferents to the medial pallium is presently uncertain, based on our electrophysiological recordings and previous anatomical studies it seems likely that the ventral striatum is the next ascending area above the auditory thalamus in the anuran auditory pathway.
Male Puerto Rican treefrogs, Eleutherodactylus coqui, produce a two-note call: a 100-msec constant frequency 'Co' note, followed by a longer, upward sweeping 'Qui' note. Previous behavioral studies have shown that males respond selectively to natural and synthetic call notes of 100 msec duration, whereas preliminary results suggest that females respond preferentially to the second note in the male's call. In the present study, we first show that the basilar papilla in the inner ear is tuned differentially in males and females. Comparisons were next made between cells in the eighth nerve and midbrain torus semicircularis of firing rate vs. duration functions in order to help determine the underlying neural mechanisms responsible for the behavioral selectivity to notes of 100 msec duration. A model for detection of vocalizations of specific durations is postulated and discussed in the light of the observed calling behavior of the male as well as the response properties of a class of cells found in the torus semicircularis.
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Anurans (frogs and toads) represent an example of peripheral specialization of the auditory systems. Their inner ear contains two distinct auditory organs: the amphibian papilla and the basilar papilla. Each organ is tuned to different species-specific frequency ranges. Because of this peripheral specialization, anurans offer an excellent opportunity to explore neural decoding of complex sounds in the central auditory system.
A single 2-hour exposure to auditory stimulation at any point during the final 3 days of incubation accelerates the hatching of Japanese quail. The 3-day sensitive period includes both prenatal and perinatal stages of incubation. So far as is known these results provide the first unequivocal evidence that short-term prenatal sensory stimulation can affect the development of an avian embryo.
Right or left eye primordia of Shumway stage 16-18 Rana pipiens embryos were transplanted to the position normally occupied by the ear, where they developed into externally normal eyes. Ganglion cell density in the retina of the transplanted eye was significantly lower than the ganglion cell density in the animal's normal eyes. No significant difference was observed between normal and transplanted inner and outer nuclear layers. In several preparations a large piece of embryonic forebrain was included in the initial eye graft. Optic nerves from the transplanted eyes penetrated this transplanted forebrain and established a dorsocaudal growth trajectory relative to the ectopic tissue's original anterior-posterior and dorsal-ventral axes. After traversing the forebrain, the transplanted optic nerve fibers penetrated the medulla where they invaraibly grew dorsocaudally to take up and maintain a dorsolateral position in the white matter of the spinal cord. The consistent dorsocaudal trajectory established by the translocated optic tract in the ectopic forebrain and in the hindbrain and spinal cord is very similar to the growth trajectory in the normal diencephalon, suggesting that dorsocaudal growth relative to the three major axes of the neural tube is an inherent property of optic nerve fibers. These results also suggest that the polarity cues which guide normal optic tract growth are not unique to the diencephalic regions of the neural tube.
When a primordial eye was transplanted to the ear position in Rana pipiens embryos, the optic nerve from the ectopic eye penetrated the medulla and invariably established a tract in the dorsolateral white matter of the ipsilateral spinal cord. In response to visual stimulation of the transplanted eye, extracellular recordings with metal microelectrodes were conducted with the spinal cords of post-metamorphic animals. Visual activity in the spinal cord could only be recorded in those experimental animals in which the transplanted optic nerve succeeded in penetrating the medulla. This activity was frequently encountered in the gray matter of the cord well below the dorsolateral position of the transplanted optic tract. The discharge characteristics and adaptation properties of the visual activity were often similar to that of optic nerve fibers from normal eyes suggesting that axons or their collaterals branch off from the transplanted optic tract and arborize within the spinal cord. However, occassionally stimulation of the transplanted eye evoked activity with adaptation and/or response characteristics unlike that of normal optic nerve fibers. Visual activity in the spincal cords of our experimental animals could be driven by moving small dark objects within circumscribed regions in the visual field of the transplanted eye. However we were unable to find any evidene of a systematic mapping of the transplanted retina within these abnormally penetrated spinal cords.
Acoustic playback experiments with calling males in their natural habitat and two-choice orientation experiments with females indicate that males and females of the neotropical tree frog Elutherodactylus coqui respond to different notes in the two-note call of the male. This functional dichotomy of the two notes in the male's call reflects a difference in the distribution of the best excitatory frequencies of primary auditory neurons for the males and females. To the best of our knowledge, Eleutherodactylus is the first known example of a vertebrate in which the peripheral auditory sensitivity shows a sexual difference.
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1. The response patterns of single cells to monaural and binaural acoustic stimuli were studied in the dorsal medullary nucleus of the bullfrog (Rana catesbeiana). This nucleus represents the first ascending center in the anuran's central auditory nervous system. 2. Of the 142 cells isolated, 75 units responded only to monaural stimulation. Approximately 80% of these monaural cells could be excited by the ipsilateral ear, while the remaining 20% received their excitatory input from the contralateral ear. The other 67 units responded to binaural stimuli. Of these binaural cells, 14 could be excited by either contralateral or ipsilateral stimuli, and the threshold and best excitatory frequency were similar for each ear (EE). The other 53 binaural cells (EI) could be excited by stimulation of one ear and inhibited by stimulation of the other ear; for almost all of these cells the contralateral ear was excitatory and the ipsilateral ear was inhibitory. The best inhibitory frequency for one ear was approximately the same as the best excitatory frequency for the other ear, and the threshold for inhibition was near the threshold for excitation. 3. The tuning curves for all of the cells in the dorsal medullary nucleus were unimodal with "Q" values ranging from 0.4 to 4. The excitatory thresholds were widely scattered between 22 and 115 dB SPL. 4. The distribution of best excitatory frequencies for the monaural cells comprised three groups: 200-300, 500-800, and 900-1,600 Hz. The best excitatory frequencies of the binaural cells were scattered over this entire range, with a broad peak around 200-800 Hz. 5. Approximately 80% of the cells in the dorsal nucleus responded tonically throughout the duration of an excitatory tone burst. The remaining 20% of the cells responded phasically during the transient stages of a tone burst over a wide intensity range. 6. Response latencies were compared for the two types of monaural cells to tones at their best exciatatory frequencies at 10 dB above threshold. The latencies for the contralaterally excitable cells were just a few milliseconds longer than the latencies for the ipsilaterally excitable cells. For binaural cells the latency for contralateral stimulation was only 1-2 ms longer than for ipsilateral stimulation. It was concluded that the contralateral input to the dorsal medullary nucleus is not of efferent descending origin from higher auditory centers. 7. All of the binaural EI cells were sensitive to small interaural intensity differences and many were also sensitive to minute interaural time differences. These cells likely play a role in localization of sounds of significance to anurans.
A new microelectrode implantation technique is described for recording electrical activity in the brains of awake, unrestrained small animals. The technique employs a miniature heating element and wax seal to enable movement of the microelectrode. Preliminary results in toads (Bufo americanus) are presented as an example of the technique.
We describe an optical technique for measurement of mechanical vibrations in the auditory organs of living animals. The technique uses light scattered from the vibrating structure and offers several new advantages. Better than 1 angstrom sensitivity, 10 micrometers spatial resolution, and > 70 decibels dynamic range are achieved. Illustrative measurements of the mechanical response of the tympanic membrane of crickets (Gryllidae) are reported.
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