摘要:

The paratympanic organ (Vitali organ) is a small sensory organ in the middle ear of birds. It possesses a sensory epithelium with hair cells similar to those of the inner ear. Injection of fluorescent carbocyanine tracers into the paratympanic organ of 9- to 11-day-old chick embryos labeled ganglion cells in the facial ganglia. Paratympanic nerve fibers enter the brainstem with the facial nerve but proceed to vestibular brainstem nuclei. A dorsal branch terminates in ventral areas of the cerebellum, while a ventral component projects to the descending vestibular nucleus, with some fibers turning medially into lateral parts of the medial vestibular nucleus. No fibers were labeled in the motor or sensory facial nucleus or in auditory brainstem nuclei. This projection pattern suggests a function of the paratympanic organ in equilibrium rather than audition. Projections similar to those of the paratympanic nerve have been reported for the lagenar nerve. Immunocytochemical techniques using an antiserum to gamma-aminobutyric acid (GABA) demonstrate that hair cells in the paratympanic organ develop GABA immunoreactivity at 5 days of incubation (E5), 2–4 days earlier than GABA immunoreactivity can be detected in hair cells of the inner ear, i.e. in the saccule (E6.5–7.0), the utricle (E7),the cristae (E8–9) and the cochlea (E9–9.5). Afferent fibers that are transiently GABAergic are rare in the paratympanic organ (1–2 fibers), though present from E6 to E7.5. The early onset of GABA immunoreactivity in the paratympanic organ may indicate that this organ matures (and possibly functions) earlier in ontogenetic development than its counterparts located in the inner ear. The present findings are consistent with the hypothesis that the paratympanic organ is homologous with the spiracular organ of fishes. The paratympanic organ of birds may represent a sense organ that is derived phylogenetically and ontogenetically from the lateral-li

ISSN:0006-8977    

DOI:10.1159/000115851

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

In this study we have used retrogradely transported horseradish peroxidase (HRP) to investigate whether the nucleus prepositus hypoglossi of a lateral-eyed mammal projects to the oculomotor and trochlear nuclei. After the injection of HRP in the oculomotor nucleus of rabbits, labelled neurons were found bilaterally in the nucleus prepositus hypoglossi, though they were more numerous on the ipsilateral side. The majority of these neurons were labelled in the rostral part of the propositus nucleus and were dispersed predominantly in the lateral and ventral zone of the nucleus. Neurons were also labelled in the prepositus nucleus after injection of HRP in the trochlear nucleus. These data were compared with those for frontal-eyed mammals and birds and suggest that the said projections are less well developed in species that possess panoramic vision and a lesser degree of binocular yoking.

ISSN:0006-8977    

DOI:10.1159/000115852

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Vital staining and scanning electron microscopy were used to study the morphology of superficial neuromasts in the blind cave fish, Astyanax hubbsi, and its sighted congener, Astyanax mexicanus. In blind Astyanax the neuromasts are 80 x 50 µm in size and possess cupulae with an oval basal shape. The length of the cupula is correlated to the location of its neuromast. Head neuromasts were found to have the longest cupulae (up to 300 µm), and caudal neuromasts have the smallest. Cupulae of all lengths have been observed to be easily bent by water movements. The neuromasts are directionally sensitive in that the bending of their cupulae perpendicular to the longer axis of the cupulae provides maximal excitation. A comparison of superficial neuromasts in the blind A. hubbsi to those in sighted A. mexicanus revealed several structural differences. The neuromasts in the blind fish are twice as large. Their cupulae, in particular, are much longer and seem to have supporting attachments at their edges. The greater length of the cupulae in blind cave fish may be of particular importance for the functioning of the lateral line organ, since longer cupulae protrude beyond the boundary layer in faster water currents and thus can increase the sensitivity of the neuromasts. The specific morphology of the neuromasts in the blind cave fish appears to reflect an evolutionary adaptation which can serve to improve the functioning of the lateral line system and thereby compensate for the lack of eye

ISSN:0006-8977    

DOI:10.1159/000115853

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The efferent projections from the visual thalamus to the Wulst were studied in the little owl, Athene noctua. Cells of origin were identified by retrograde labeling after injections of wheat-germ-agglutinin-conjugated horseradish peroxidase into the Wulst. The labeled-cell distribution was correlated with the distribution of anterogradely labeled retinal terminals as revealed by intraocular injections of horseradish peroxidase. The results demonstrated a bilateral thalamofugal visual pathway ascending from the nucleus dorsolateral anterior thalami (DLA). Projections from the visual thalamus to the Wulst showed a specific and orderly pattern and retrogradely labeled cells of DLA were distributed equally, in a complementary fashion, on both sides of the brain, with a small region of overlap. Retinal termination fields in DLA largely overlapped relay neurons projecting to either Wulst, although the overlap was not complete. Despite differences in the organization of avian and mammalian visual pathways, which reflect their separate evolutionary origins, similarities between the DLA in the little owl and the lateral geniculate nucleus in mammals suggest that, during evolution similar selective pressures for binocularity led to a similar morphological organization.

ISSN:0006-8977    

DOI:10.1159/000115854

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

Visually evoked potentials (VEPs) have been recorded from the Wulst surface of the little owl, Athene noctua, in response to counterphase-reversal of sinusoidal gratings with different contrast, spatial frequency and mean luminance, presented either monocularly or binocularly. Monocular full-field stimuli presented to either eye evoked VEPs of similar amplitude, waveform and latency. Under binocular viewing, VEPs approximately doubled in amplitude without waveform changes. VEPs with similar characteristics could be obtained in response to stimulation of the contralateral, but not ipsilateral, hemifield. These results suggest that a 50% recrossing occurs in thalamic efferents and that different ipsilateral and contralateral regions converge onto the same Wulst sites. The VEP amplitude progressively decreased with increase of the spatial frequency beyond 2 cycles/degree, and the high spatial frequency cutoff (VEP acuity) was under binocular viewing (8 cycles/degree) higher than under monocular (5 cycles/degree) viewing (200 cd/m22), but the binocular VEP amplitude did not change either by changing the stimulus orientation (horizontal vs. vertical gratings) or by inducing different retinal disparities. These results indicate that VEPs can serve as a useful tool to measure visual performance in owls under different stimulus conditions in their operative range. Under low-luminance, high-contrast conditions, binocular visual performance, compared to monocular performance appears to improve by a factor of more than √2 (probability summation). This binocular advantage occurs independent of stere

ISSN:0006-8977    

DOI:10.1159/000115855

出版商:S. Karger AG    

年代:1990

数据来源: Karger

摘要:

The organization of presumptive dopamine- and norepinephrine-synthesizing neurons in the brains of goldfish is described by using antibodies to tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) with avidin-biotin immunocytochemical techniques. In the hindbrain, TH-immunoreactive (IR) and DBH-IR cell bodies are located together in the following three regions: (1) dorsomedial medulla in the post-obecular region, (2) medullary tegmentum from the level of the greatest expansion of the vagal lobes to the medullospinal transition, and (3) isthmal tegmentum dorsolateral to the medial longitudinal fasciculus. Elsewhere in the brain, TH-IR neurons were visualized in eight distinct forebrain neuronal groups; DBH-IR cell bodies were not observed. Fibers and terminals IR for TH and DBH were most dense in forebrain periventricular regions, i.e. adjacent to the third ventricle, and specifically around the lateral and preoptic recesses. In the telencephalon, a dense innervation of TH- and DBH-IR fibers was noted within the area dorsalis, pars lateralis and pars dorsalis. Within the area dorsalis, pars centralis TH-IR fibers were dense; DBH-IR fibers were not visualized in this region. The presence of both dopamine- and norepinephrine-synthesizing neurons in the isthmal and medullary tegmentum and in the dorsomedial medulla provides evidence indicating that these regions are homologous to the locus ceruleus, medullary reticular nucleus and area postrema, respectively, in tetrapod brains. In addition, the remarkably dense innervation of TH-IR and DBH-IR fibers and terminals in periventricular regions of the hypothalamus and within the telencephalon suggests that there are potential similarities in the catecholaminergic innervation of forebrain regions of teleost and mammalian brains

ISSN:0006-8977    

DOI:10.1159/000115856

出版商:S. Karger AG    

年代:1990

数据来源: Karger