Ascending connections of a thalamic auditory area in a crocodile,Caiman crocodilus (original) (raw)
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The Journal of Comparative Neurology, 1975
Nucleus rotundus receives a major input from the optic tectum in crocodiles, C a i m a n crocodilus. Telencephalic projections of nucleus rotundus were studied in C a i m a n by means of the Fink-Heimer procedure after anodal, stereotaxic lesions. Efferent axons of nucleus rotundus assemble on the ventromedial aspect of this nucleus and swing ventrolaterally to enter the dorsal peduncle of the lateral forebrain bundle. These ascending fibers continue rostrally in the dorsal peduncle of the lateral forebrain bundle to enter the telencephalon where they remain restricted to a lateral portion of the lateral forebrain bundle. At more anterior levels, these fascicles turn dorsally, pass through the ventrolateral area, and terminate massively in a lateral part of the rostral dorsolateral area.
A second auditory area in the non-cortical telencephalon of a reptile
Brain Research, 1992
Injections of horseradish peroxidase (HRP) into a caudocentral portion of the non-cortical telencephalon of Caiman known as the dorsolateral area (dorsal ventricular ridge) resulted in retrogradely labeled neurons throughout the entire extent of the ipsilateral nucleus reuniens. HRP-positive cells were most numerous in nucleus reuniens pars diffusa with only sparse labeling of neurons in nucleus reuniens pars centralis. The results of the present experiment, when compared with those of a prior study that determined the teleneephalic connections of nucleus reuniens pars centralis, suggested that these two forebrain areas are separate. Staining with suceinate dehydrogenase and acetylcholinesterase revealed that nucleus reuniens pars centralis and pars diffusa and their respective telencephalic projection areas can be differentiated on the basis of histochemical features. These findings in Caiman suggest that certain thaiamic and telencephalic auditory areas in birds and crocodilians are most likely the result of common ancestry rather than examples of parallel evolution.
Brain Research, 1977
Telencephalic auditory and visual regions in crocodiles have been identified by following the course and distribution of degenerating axons that result from stereotaxic lesions of certain neuronal aggregates in the thalamus. One such area, nucleus reuniens pars centralis, which receives bilateral auditory input from the central nucleus of the torus semicircularis 7, projects to a caudomedial portion of the dorsal ventricular ridge 8. Another diencephalic region, nucleus rotundus, which receives bilateral visual afferents from the optic rectum 2, projects to an anterolateral portion of the dorsal ventricular ridge 0. Furthermore, the dorsal ventricular ridge of crocodiles, as well as that of other reptiles and birds, shares certain properties in common with neocortical areas in mammals 5,10. In fact, some have suggested that the dorsal ventricular ridge of birds and reptiles is homologous to certain neocortical areas in mammals 5. Regardless of its similarities with mammalian neocortex, the dorsal ventricular ridge of crocodiles merits study because it is the highest sensory integration center in this group of reptiles.
Brain Research, 1986
Key words: dorsal ventricular ridge --intrinsic neuron --local circuit neuron --relay cell --reptile --thalamus Large injections of horseradish peroxidase were placed in the non-cortical telencephalon in a reptile, Caiman crocodilus. The number of retrogradely labeled and unlabeled neurons in two sensory thalamic nuclei, nucleus rotundus (vision) and nucleus reuniens pars centralis (audition) were counted. The percentage of unlabeled cells in each nucleus was less than 1%. These data suggest that each of these thalamic nuclei contain few, if any, intrinsic or local circuit neurons.
Midbrain projecting dorsal column nucleus neurons in a reptile
Brain Research Bulletin, 2002
The origin of midbrain projecting cells in the dorsal column nucleus (DCN) was investigated in reptiles, Caiman crocodilus, using a retrograde tracer. Labeled neurons were confined to a caudal-central portion of the DCN. Midbrain projecting DCN neurons had round, oval, or triangular soma and were small. While neurons that project to the spinal cord in Caiman are also located in the caudal half of the DCN, midbrain projecting cells are located more dorsally and are smaller than those whose axons terminate in the spinal cord. Taken together, these observations suggest that the DCN in Caiman is subdivided, at least in part, according to target location. In view of similar findings in certain birds and mammals, subdivisions of the DCN into sectors is likely a phylogenetically ancient feature of amniote sensory systems transmitting somatosensory information from the body surface.
Afferents to the midbrain auditory center in the bullfrog,Rana catesbeiana
The Journal of Comparative Neurology, 1981
Horseradish peroxidase (HRP) histochemistry was used to visualize cells afferent to the bullfrog torus semicircularis. These afferent cells are located in several sensory and nonsensory nuclei. The sensory structures which project to the torus are mainly auditory nuclei, with the major input coming from the ipsilateral superior olive. A very small contralateral projection is also present. In addition, afferents arise from the contralateral, and to a lesser extent ipsilateral, dorsal acoustic nucleus and nucleus caudalis, both primary eighth nerve nuclei. A vestibular input is also apparent in that HRP-positive cells were seen in the magnocellular vestibular nucleus and among elongated bipolar cells a t the ventral border of the eighth nerve nuclei. In addition, the torus receives somatosensory input from the contralateral perisolitary band. Afferents from spinal cord cells proved difficult to visualize. Nonsensory areas throughout the brain innervate the torus as well. In the medulla, HRP-positive cells were present bilaterally in both medial and lateral reticular areas. The tegmentum contributes a major input from the superficial isthmal reticular nucleus and a minor input from the tegmental fields. Commissural toral projections are also present. Descending forebrain input arises from the pretectal gray bilaterally, the ventral half of the ipsilateral lateral pretectal nucleus, and, possibly, from the ipsilateral posterior thalamic nucleus. HRP-positive cells were also occasionally seen in the posterior tuberculum, ventral hypothalamus, and caudal suprachiasmatic preoptic area. Finally, a telencephalic projection from the ipsilateral anterior entopeduncular nucleus is present.
The Journal of Comparative Neurology, 2012
We used tract tracing to reveal the connections of the auditory brainstem in the Tokay gecko (Gekko gecko). The auditory nerve has two divisions, a rostroventrally directed projection of mid-to high best-frequency fibers to the nucleus angularis (NA) and a more dorsal and caudal projection of low to middle best-frequency fibers that bifurcate to project to both the NA and the nucleus magnocellularis (NM). The projection to NM formed large somatic terminals and bouton terminals. NM projected bilaterally to the second-order nucleus laminaris (NL), such that the ipsilateral projection innervated the dorsal NL neuropil, whereas the contralateral projection crossed the midline and innervated the ven-tral dendrites of NL neurons. Neurons in NL were generally bitufted, with dorsoventrally oriented dendrites. NL projected to the contralateral torus semicircularis and to the contralateral ventral superior olive (SOv). NA projected to ipsilateral dorsal superior olive (SOd), sent a major projection to the contralateral SOv, and projected to torus semicircularis. The SOd projected to the contralateral SOv, which projected back to the ipsilateral NM, NL, and NA. These results suggest homologous patterns of auditory connections in lizards and archosaurs but also different processing of low-and high-frequency information in the brainstem. J. Comp. Neurol. 520:1784-1799, 2012