Hair cell regeneration after local application of gentamicin at the round window of the cochlea in the pigeon

Hair cells in the basilar papilla of birds have the capacity to regenerate after injury. Methods commonly used to induce cochlear damage are systemic application of ototoxic substances such as aminoglycoside antibiotics or loud sound. Both methods have disadvantages. The systemic application of antibiotics results in damage restricted to the basal 50% of the papilla and has severe side effects on the kidneys. Loud sound damages only small parts of the papilla and is restricted to the short hair cells. The present study was undertaken to determine the effect of local aminoglycoside application on the physiology and morphology of the avian basilar papilla. Collagen sponges loaded with gentamicin were placed at the round window of the cochlea in adult pigeons. The time course of hearing thresholds was determined from auditory brain stem responses elicited with pure tone bursts within a frequency range of 0.35–5.565 kHz. The condition of the basilar papilla was determined from scanning electron micrographs. Five days after application of the collagen sponges loaded with gentamicin severe hearing loss, except for the lowest frequency tested, was observed. Only at the apical 20% of the basilar papilla hair cells were left intact, all other hair cells were missing or damaged. At all frequencies there was little functional recovery until day 13 after implantation. At frequencies above 1 kHz functional recovery occurred at a rate of up to 4 dB/day until day 21, beyond that day recovery continued at a rate below 1 dB/day until day 48 at the 5.6 kHz. Below 1 kHz recovery occurred up to day 22, the recovery rate was below 2 dB/day. A residual hearing loss of about 15–25 dB remained at all frequencies, except for the lowest frequency tested. At day 20 new hair cells were seen on the basilar papilla. At day 48 the hair cells appeared to have recovered fully, except for the orientation of the hair cell bundles. The advantage of the local application of the aminoglycoside drug over systemic application is that it damages almost all hair cells in the basilar papilla and it has no toxic side effects. The damage is more extensive than with systemic application.     

Spontaneous activity of the Purkinje cells in the pigeon cerebellum

Summary In intact and decerebrate pigeon, both under barbiturate anaesthesia, the spontaneous activity of single Purkinje cells has been analysed.The average frequency of the simple spikes was similar to that described in mammals and was essentially the same in the intact and decerebrate preparations. The average frequency of the complex spikes was higher than that found in mammals and it was significantly depressed in the decerebrate pigeon as compared with the intact one. The amount of the depression, however, was less than that described in mammals.For the simple spikes a correlation was found between the mean interspike interval and both the standard deviation and the percentage of intervals at the mode. The correlation indicates that as the frequency increases the firing tends to become more regular. The same conclusion applies to the complex spikes, although in this case the only significant correlation was between the mean interval and standard deviation.Interval histograms of simple spikes were usually unimodal, but were occasionally also bimodal in both intact and decerebrate pigeons. Interval histograms of complex spikes were usually multimodal with many peaks at regular intervals, the highest peak not necessarily being the first one. The duration of the basic interval varied in different cells from 65 to 130 ms.The probability of firing of the simple spikes is always reduced following the appearance of a complex spike. The duration of the pause is related to the frequency of the simple spikes; the higher the frequency, the shorter the pause.     

Stimuli and the texture of experience

Evidence from human language learning and stimulus control of learned and unlearned behavior suggests that generalization and categorization are based on principles of similarity that have evolved to favor the perception of recurrent events and extended objects. The perceptual similarities are typically more complex than, and only occasionally approximated by, physical similarity. In some, but not all, cases, perceptual similarity is tantamount to innate knowledge.     

Vitreal and intraretinal responses to contrast reversing patterns in the pigeon eye

The pattern electroretinogram (PERG) has been recorded vitreally and intraretinally in the pigeon eye. The amplitude of the PERG increases monotonically as pattern contrast is increased, with saturation at high levels. The PERG of the central yellow field has band-pass spatial tuning, with a high frequency cut-off at at 8 c/deg. Time-to-peak is shortest at low spatial frequencies. Both PERG and local b-wave are small and positive-going close to the retinal surface, and large and negative-going in the inner nuclear layer. The PERG and b-wave show qualitatively similar depth profiles.     

Comparative, in vitro, studies of hippocampal tissue from homing and non-homing pigeon

The purpose of this research was to characterize morphologically and electrophysiologically tissue slices obtained from the hippocampus of homing and non-homing pigeons. When hippocampal slices from the brain of homing and non-homing pigeons are observed under the dissecting microscope, diffuse fiber paths can be seen. These fiber pathways appeared to be identical with the medial fiber tract (VM) previously described histologically in the hippocampus of homing pigeon. Visualization of these tracts in living slices allowed placement of stimulating and recording electrodes in corresponding locations in these slices in both homing and non-homing pigeons. Extracellular potentials recorded from VM regions of the brains of both homing and non-homing pigeons were sensitive to CNQX indicating that glutamate may be a neurotransmitter in this area of pigeon hippocampus. These potentials could undergo long-term potentiation (LTP) following high frequency stimulation. This LTP was blocked by NMDA receptor antagonist APV in the hippocampus of homing pigeon, but was APV-resistant in the hippocampus of non-homing pigeon. Extracellular potentials from the hippocampus of homing pigeons were increased in amplitude when slices were perfused with Mg²⁺-free Ringer, while potentials recorded from hippocampal slices from non-homing pigeons were unaffected by Mg²⁺-free solutions. Intracellular recordings from the hippocampal slices of homing pigeons revealed that about half the cells demonstrated excitatory synaptic potentials evoked by extracellular stimulation. The EPSP was sometimes large enough to trigger an action potential. Neurons filled with the fluorescent dye, Lucifer Yellow, in the hippocampus of homing pigeons showed multipolar structure. The response of these cells to extracellular stimulation provides the activity responsible for the extracellular potentials which can undergo LTP.     

Hypophagic and Dipsogenic Effects of Central 5-HT Injections in Pigeons

The present work describes a series of experiments designed to examine the possible role of central 5-HT circuits in the control of feeding and drinking in pigeons. Acute effects (within 1 h) of intracerebroventricular (ICV) injections of 5-HT (0, 9.7, 19.4, 38.7, 77.5, 155, and 310 nmol) in 24-h food-deprived (24FD) pigeons included strong hypophagic and dipsogenic responses at the three higher doses. Total food intake and the duration of feeding behavior were reduced, and latency for the start of eating increased. Total 1-h water intake in 5-HT–treated pigeons usually increases to reach a volume equivalent to 10% of their body weight. Similarly, potent dipsogenic effects of ICV 5-HT, but no food intake decreases, were observed in food-satiated animals. Feeding behavior induced by ICV injection of adrenaline (30 nmol) in satiated pigeons was abolished by previous (20 min before) ICV 5-HT (155 nmol) injections. Catecholamine treatment did not affected the dipsogenic effect of 5-HT injections. Decreases in food intake were similarly observed after ICV or subcutaneous injections of equimolar 5-HT doses (155 nmol) in 24FD pigeons, but systemic 5-HT injections evoked no drinking behavior. Central injections of the 5-HT_2a/2c agonist DOI (56 nmol) induced similar decreases in duration and amount of food intake in 24FD animals. No dipsogenic effect was observed with either DOI doses. In 24FD pigeons, the 5-HT_1a agonist 8-OH-DPAT (30.5 nmol) induced strong dipsogenic effects, as well as increase in food intake duration. These data may indicate an involvement of 5-HT circuits in food intake as well as in water intake control systems in the pigeon, and that serotoninergic effects in these functional domains are mediated by independent mechanisms.     

Lateralization of visually controlled behavior in pigeons

Pigeons were trained binocularly on two different successive pattern discrimination tasks. After reaching criterion they performed the tasks with either the left or the right eye occluded or with both eyes unobstructed. The number of responses emitted was greater when the right rather than the left eye was uncovered. Also the percent correct discrimination scores were better when seeing with the right eye than with the left one. Some pigeons originally acquired the discrimination monocularly, generally using the right eye, although both eyes were uncovered. The results are discussed in relation to brain structures that may mediate this performance.     

The visual fields of the tawny owl, Strix aluco L

The uniocular retinal field of Strix aluco is highly asymmetrical. The maximum width of 124 degrees is less than that recorded in any other vertebrate. Maximum retinal binocular field width equals 48 degrees and the optic axes diverge by 55 degrees. Maximum binocularity occurs above the bill whose tip lies outside of the visual field. The cyclopean retinal field has a maximum width of 201 degrees. Limited data on the visual fields of the pigeon are also presented. All of these data are compared with visual field widths in other species and the significance of the owl eye's tubular shape, its nasad asymmetry, and the possible factors influencing binocular field width are discussed.     

Mirror image discrimination with each eye in pigeons.

Three groups of pigeons were monocularly trained on discrimination with each eye. The animals which were trained on a mirror image discrimination with one eye and a reversed mirror image discrimination with the other eye, and the animals which were trained on a mirror image discrimination with one eye and a horizontal-vertical discrimination with the other eye did not show any difficulty in learning of these tasks. There is no significant difference between the two groups in the numbers of training sessions necessary to reach the criterion. On the other hand, the animals which were trained on a same mirror image discrimination with each eye showed difficulty in learning of the task. This group required longer training to learn the task than did the other two groups. These results suggest that the mirror image reversal effect appeared as a disturbing effect but not as a facilitative effect during the parallel learning with each eye.     

The spatial organization of the excitatory regions in the visual receptive fields of the pigeon's optic tectum

Summary The spatial location of the excitatory regions in the receptive field of cells in the pigeon's optic tectum was analyzed with light and dark edges moving at a constant velocity. The tectal cells were classified into two main groups: 1-cells showing spatially overlapping light and dark excitatory regions in their receptive field (60%); cells showing spatially separated light and dark excitatory regions in their receptive field (32%). A small number of cells discharged only to one sign of contrast. These results were confirmed by testing the cells with light bars of various widths. Latency studies were carried out with single edges moving at a series of constant velocities. In most cases, for any given cell the light and the dark edge discharges were shown to have similar latencies. These results also indicate that the relative location of the excitatory regions in the receptive field of most tectal cells was not significantly affected by the latency of the discharges.Supported by grants from the CNRS (ERA No. 333; ATP No. 4185) and from DGRST (79.7.1075)