A Stereotaxic Atlas of the Brain of the Chick (Gallus domesticus)

Nine brains taken from chicks two weeks of age were used for the development of this atlas. Each chick was first anesthetized with an intravenous (IV) injection of Chloropent2 (1.8 ml/kg). Chicks were then perfused via the heart with 90 ml physiological saline followed by 90 ml Heidenhain\u27s3 solution. Each head was then positioned in a stereotaxic instrument as described in the previous section and three stainless steel (SS) insect pins (#2) were implanted in each brain at known coordinates. In the case of the brains used to construct the cross- sectional atlas plates, two pins were implanted horizontal to the base of the stereotaxic instrument. Each was inserted into the forebrain and the pins exited either the brainstem or the cerebellum. The third pin was inserted vertical to the base of the stereotaxic instrument. The brains used to construct the sagittal atlas plates had two pins inserted horizontally and one pin inserted vertically to the stereotaxic instrument. The horizontal pins entered the right side of the brain and exited the left side. The brains used for the horizontal plates had two pins inserted vertically and one pin horizontally. The latter entered the forebrain and exited the brainstem

Mechanisms of Feedback in the Visual System

Feedback is an ubiquitous feature of neural systems though there is little consensus on the roles of mechanisms involved with feedback. We set up an in vivo preparation to study and characterize an accessible and isolated feedback loop within the visual system of the leopard frog, Rana pipiens. We recorded extracellularly within the nucleus isthmi, a nucleus providing direct topographic feedback to the optic tectum, a nucleus that receives the vast majority of retinal output. The optic tectum and nucleus isthmi of the amphibian are homologous structures to the superior colliculus and parabigeminal nucleus in mammals, respectively. We formulated a novel threshold for detecting neuronal spikes within a low signal-to-noise environment, as exists in the nucleus isthmi due to its high density of small neuronal cell bodies. Combining this threshold with a recently developed spike sorting procedure enabled us to extract simultaneous recordings from up to 7 neurons at a time from a single extracellular electrode. We then stimulated the frog using computer driven dynamic spatiotemporal visual stimuli to characterize the responses of the nucleus isthmi neurons. We found that the responses display surprisingly long time courses to simple visual stimuli. Furthermore, we found that when stimulated with complex contextual stimuli the response of the nucleus isthmi is quite counter-intuitive. When a stimulus is presented outside of the classical receptive field along with a stimulus within the receptive field, the response is actually higher than the response to just a stimulus within the classical receptive field. Finally, we compared the responses of all of the simultaneously recorded neurons and, together with data from in vitro experiments within the nucleus isthmi, conclude that the nucleus isthmi of the frog is composed of just one electrophysiological population of cells

Winner-take-all selection in a neural system with delayed feedback

We consider the effects of temporal delay in a neural feedback system with excitation and inhibition. The topology of our model system reflects the anatomy of the avian isthmic circuitry, a feedback structure found in all classes of vertebrates. We show that the system is capable of performing a `winner-take-all' selection rule for certain combinations of excitatory and inhibitory feedback. In particular, we show that when the time delays are sufficiently large a system with local inhibition and global excitation can function as a `winner-take-all' network and exhibit oscillatory dynamics. We demonstrate how the origin of the oscillations can be attributed to the finite delays through a linear stability analysis.Comment: 8 pages, 6 figure

Visual and Electrosensory Circuits of the Diencephalon in Mormyrids

Mormyrids are one of two groups of teleost fishes known to have evolved electroreception, and the concomitant neuroanatomical changes have confounded the interpretation of many of their brain areas in a comparative context, e.g., the diencephalon, where different sensory systems are processed and relayed. Recently, cerebellar and retinal connections of the diencephalon in mormyrids were reported. The present study reports on the telencephalic and tectal connections, specifically in Gnathonemus petersii, as these data are critical for an accurate interpretation of diencephalic nuclei in teleosts. Injections of horseradish peroxidase into the telencephalon retrogradely labeled neurons ipsilaterally in various thalamic, preglomerular, and tuberal nuclei, the nucleus of the locus coeruleus (also contralaterally), the superior raphe, and portions of the nucleus lateralis valvulae. Telencephalic injections anterogradely labeled the dorsal preglomerular and the dorsal tegmental nuclei bilaterally. Injections into the optic tectum retrogradely labeled neurons bilaterally in the central zone of area dorsalis telencephali and ipsilaterally in the torus longitudinalis, various thalamic, pretectal, and tegmental nuclei, some nuclei in the torus semicircularis, the nucleus of the locus coeruleus, the nucleus isthmi and the superior reticular formation, basal cells in the ipsilateral valvula cerebelli, and eurydendroid cells in the contralateral lobe C4 of the corpus cerebelli. Weaker contralateral projections were also observed to arise from the ventromedial thalamus and various pretectal and tegmental nuclei, and from the locus coeruleus and superior reticular formation. Tectal injections anterogradely labeled various pretectal nuclei bilaterally, as well as ipsilaterally the dorsal preglomerular and dorsal posterior thalamic nuclei, some nuclei in the torus semicircularis, the dorsal tegmental nucleus, nucleus isthmi, and, again bilaterally, the superior reticular formation. A comparison of retinal, cerebellar, tectal, and telencephalic connections in Gnathonemus with those in nonelectrosensory teleosts reveals several points: (1 the visual area of the diencephalon is highly reduced in Gnathonemus, (2) the interconnections between the preglomerular area and telencephalon in Gnathonemus are unusually well developed compared to those in other teleosts, and (3) two of the three corpopetal diencephalic nuclei are homologues of the central and dorsal periventricular pretectum in other teleosts. The third is a subdivision of the preglomerular area, rather than an accessory optic or pretectal nucleus, and is related to electroreception. The preglomerulo-cerebellar connections in Gnathonemus are therefore interpreted as uniquely derived characters for mormyrids

Afferent connections of the valvula cerebelli in two teleosts, the common goldfish and the green sunfish

The afferent connections of the valvula cerebelli were examined in one cypriniform teleost (Carassius auratus) and one perciform teleost (Lepomis cyanellus) with the use of horseradish peroxidase as a retrograde tracer. Both species have ipsilateral input to the valvula from the central pretectal and dorsal accessory optic nuclei, the dorsal and ventral tegmental nuclei, the lateral nucleus of the valvula, the perilemniscal nucleus, and nucleus isthmi and contralateral input from the inferior olivary nucleus. In addition, Carassius has ipsilateral valvulopetal projections from the eminentia granularis, the praeeminential nucleus, and the isthmic primary sensory trigeminal nucleus, whereas Lepomis has bilateral (stronger ipsilaterally) valvulopetal projections from the nucleus of the locus coeruleus and the rostral corpus cerebelli. The topographical order of the cerebellopetal projections of the lateral nucleus of the valvula and inferior olive is also described, as are differential inputs to various subdivisions of the cerebellum in the two species. Information on valvulopetal projections in teleosts has thus far been limited to electroreceptive mormyrids. The present study shows that many valvular inputs related to electroreception in mormyrids have no homologue in Carassius and Lepomis. Finally, the present study indicates that the rostral part of the corpus cerebelli, but not the valvula cerebelli, in teleosts is the homologue of the anterior lobe of the corpus cerebelli in cartilaginous fishes. Thus, the valvula cerebelli is a shared derived feature (synapomorphy) of all ray-finned fishes

The Visually Related Posterior Pretectal Nucleus in the Non-Percomorph Teleost Osteoglossum bicirrhosum Projects to the Hypothalamus

This study was done to elucidate the ancestral (plesiomorphic) condition for visual pathways to the hypothalamus in teleost fishes. Three patterns of pretectal organization can be discerned morphologically and histochemically in teleosts. Their taxonomic distribution suggests that the intermediately complex pattern (seen in most teleost groups) is ancestral to both the elaborate pattern (seen in percomorphs) and the simple pattern (seen in cyprinids). The pretectal nuclei involved can be demonstrated with acetylcholinesterase histochemistry selectively and reliably in different species of teleosts, suggesting that the same-named nuclei are homologous in representatives of the three different patterns. Whereas there are visual pathways to the hypothalamus in both the elaborate (percomorph) and the simple (cyprinid) patterns, different pretectal and hypothalamic nuclei are involved. Thus visual hypothalamic pathways in these two patterns would not appear to be homologous. In this study, circuitry within the third, i.e., the intermediately complex, pattern is investigated. It is demonstrated that visual pathways project via the pretectum to the hypothalamus in Osteoglossum bicirrhosum and that they are very similar to the visual pathways in the elaborate pattern. This suggests that the circuitry in the intermediately complex pattern, as represented by Osteoglossum, is plesiomorphic (evolutionarily primitive) and the circuitry in both the simple pattern (seen in cyprinids) and the elaborate pattern (seen in percomorphs) is apomorphic (evolutionarily derived) for teleosts

The Mechanisms and Roles of Neural Feedback Loops for Visual Processing

Feedback pathways are widely present in various sensory systems transmitting time-delayed and partly-processed information from higher to lower visual centers. Although feedback loops are abundant in visual systems, investigations focusing on the mechanisms and roles of feedback in terms of micro-circuitry and system dynamics have been largely ignored. Here, we investigate the cellular, synaptic and circuit level properties of a cholinergic isthmic neuron: Ipc) to understand the role of isthmotectal feedback loop in visual processing of red-ear turtles, Trachemys scripta elegans. Turtle isthmotectal complex contains two distinct nuclei, Ipc and Imc, which interact exclusively with the optic tectum, but are otherwise isolated from other brain areas. The cholinergic Ipc neurons receive topographic glutamatergic inputs from tectal SGP neurons and project back to upper tectal layers in a topographic manner while GABAergic Imc neurons, which also get inputs from the SGP neurons project back non-topographically to both the tectum and Ipc nucleus. We have used an isolated eye-attached whole-brain preparation for our investigations of turtle isthmotectal feedback loop. We have investigated the cellular properties of the Ipc neurons by whole-cell blind-patch recordings and found that all Ipc neurons exhibit tonic firing responses to somatic current injections that are well-modeled by a leaky integrate-and-fire neuron with spike rate adaptation. Further investigations reveal that the optic nerve stimulations generate balanced excitatory and inhibitory synaptic currents in the Ipc neurons. We have also found that synaptic connection between the Imc to Ipc neuron is inhibitory. The visual response properties of the Ipc neurons to a range of computer-generated stimuli are investigated using extracellular recordings. We have found that the Ipc neurons have a localized excitatory receptive field and show stimulus selectivity and stimulus-size tuning. We also investigate lateral interactions in the Ipc neurons in response to multiple stimuli within the visual field. Finally, we quantify the oscillatory bursts observed in Ipc responses under visual stimulations

The Automation of Electrophysiological Experiments and Data Analysis

The role of computation in science is continually growing and neuroscience is no exception. Despite this, a severe lack of scientific software infrastructure persists, slowing progress in many domains. In this thesis, we will see how the combination of neuroscience and software engineering can build infrastructure that enables discovery. The first chapter discusses the Turtle Electrophysiology Project, or TEP, an experiment-automation and data-management system. This system has allowed us to automate away some of the most tedious tasks involved in conducting experiments. As a result, we can collect more data in less time, and with fewer errors related to the loss of metadata: information about how the data were collected). Also, since all of the metadata is automatically digitized during the experiment we can now completely automate our analyses. Chapters two and three are examples of research conducted using the ever-evolving TEP system. In the first instance, we used TEP to deliver visual stimuli and handle data-management. In chapter three, the experiments involved delivering electrical stimuli instead of visual stimuli, and much more rigorous analysis. And even though TEP was not specifically designed to handle collecting data this way, the flexible tags system enabled us to do so. Finally, chapter four details the construction of a robust analysis tool called Spikepy. Whereas TEP is specially designed for the turtle preparation we have, Spikepy is a general-purpose spike-sorting application and framework. Spikepy takes flexibility to the extreme by being a plugin-based framework, yet maintaining a very easy to use interface

Distribution of choline acetyltransferase (ChAT) immunoreactivity in the brain of the teleost cyprinus carpio

Cholinergic systems play a role in basic cerebral functions and its dysfunction is associated with deficit in neurodegenerative disease. Mechanisms involved in human brain diseases, are often approached by using fish models, especially cyprinids, given basic similarities of the fish brain to that of mammals. In the present paper, the organization of central cholinergic systems have been described in the cyprinid Cyprinus carpio, the common carp, by using specific polyclonal antibodies against ChAT, the synthetic enzyme of acetylcholine, that is currently used as a specific marker for cholinergic neurons in all vertebrates. In this work, serial transverse sections of the brain and the spinal cord were immunostained for ChAT. Results showed that positive neurons are present in several nuclei of the forebrain, the midbrain, the hindbrain and the spinal cord. Moreover, ChAT-positive neurons were detected in the synencephalon and in the cerebellum. In addition to neuronal bodies, afferent varicose fibers were stained for ChAT in the ventral telencephalon, the preoptic area, the hypothalamus and the posterior tuberculum. No neuronal cell bodies were present in the telencephalon. The comparison of cholinergic distribution pattern in the Cyprinus carpio central nervous system has revealed similarities but also some interesting differences with other cyprinids. Our results provide additional information on the cholinergic system from a phylogenetic point of view and may add new perspectives to physiological roles of cholinergic system during evolution and the neuroanatomical basis of neurological diseases