Formation of the Looming-evoked Innate Defensive Response during Postnatal Development in Mice / 神经科学通报·英文版

Environmental threats often trigger innate defensive responses in mammals. However, the gradual development of functional properties of these responses during the postnatal development stage remains unclear. Here, we report that looming stimulation in mice evoked flight behavior commencing at P14-16 and had fully developed by P20-24. The visual-evoked innate defensive response was not significantly altered by sensory deprivation at an early postnatal stage. Furthermore, the percentages of wide-field and horizontal cells in the superior colliculus were notably elevated at P20-24. Our findings define a developmental time window for the formation of the visual innate defense response during the early postnatal period and provide important insight into the underlying mechanism.

A Cortical Substrate for Square-Wave Jerks in Progressive Supranuclear Palsy

Anatomic study of the optical radiation and its relationship in the temporal lobe: definition of a secure approach for amigdalohipocampectomy in epilepsy surgery / Estudio anatómico de la radiación óptica y su relación en el lóbulo temporal: definición de un abordaje seguro para amigdalohipocampectomía en cirugía de la epilepsia

Introducción/Objetivos: El lóbulo temporal anterior tiene importantes estructuras subcorticales, especialmente fibras blancas que llevan la información visual. La comprensión de esta región anatómica, importantes para la práctica microquirúrgica, se basa en técnicas de disección de fibras. Ellos proporcionan perspectiva tridimensional de esta región y añaden un enfoque quirúrgico exitoso para el tratamiento de las lesiones temporales mesiales. El propósito de este trabajo es el estudio de la anatomía de la pared lateral del ventrículo lateral con el fin de determinar una zona libre de la radiación óptica. Métodos: Se diseccionaron diez hemisferios cerebrales, preparados de acuerdo con técnicas de Klingler. Se utilizan espátulas de madera con puntas de diferentes tamaños. La radiación óptica fue delimitada y las medidas se tomaron a partir de esta estructura para el polo temporal, que se utiliza como punto de referencia. Resultados: Abordajes para el cuerno temporal superior a 27 mm más allá del polo temporal pueden cruzar asa de Meyer y determinar un perjuicio a la radiación óptica con los consiguientes déficits en los campos visuales. Conclusión: La determinación de la zona de libre de fibras de radiación óptica es factible. En este trabajo se podría inferir que el área libre de la radiación óptica se encuentra en la región anterioinferior del lóbulo temporal a una distancia de hasta 2,7 centímetros desde el polo temporal y permite el acceso a el hipocampo y la amígdala durante la cirugía de la epilepsia. Resecciones más grandes que estas medidas permiten aclarar de una lesión a la radiación óptica con los consiguientes déficits en los campos visuales.

Introduction/Objective: The anterior temporal lobe has important subcortical structures, especially white fibers that lead visual information. Understanding this anatomical region, important for microsurgical practice, is based on fibers dissection techniques. They provide three-dimensional perspective for this region and add a successful surgical approach for the treatment of mesial temporal lesions. The purpose of this paper is to study the anatomy of the lateral wall of the lateral ventricle in order to determine a free area of the optical radiation. Methods: Ten cerebral hemispheres were dissected, prepared according to Klingler´s techniques. Wooden spatulas with tips of various sizes were used. The optical radiation was delimited and measures were taken from this structure to the temporal pole, used as a reference point. Results: Approaches to the temporal horn larger than 27 mm beyond the temporal pole can cross Meyer´s loop and determine injury to the optical radiation with consequent postoperatively deficits in visual fields. Conclusion: The determination of free area of optical radiation fibers is feasible. In this work we could infer that free area of optical radiation is located in the anterioinferior region of the temporal lobe at a distance of up to 2.7 centimeters from the temporal pole and allows access to the hippocampus and amygdala during epilepsy surgery. Larger resections than these measures can possibly determine injury to the optical radiation with consequent deficits in visual fields.

Development of Human Neuro-digital Slides and Neuro-atlas for Neuroscience Tutorial I (Spinal Cord and Brain Stem) / 체질인류학회지

In order to present the optimal neuroscience tutorial material for medical students and researchers, this study is aimed to make neuro-digital slide and neuro-atlas based on the histological specimens of human spinal cord and brain stem. Cadavers which had agreed for organ donation for research purpose were used in this study. Brains and spinal cords were extracted within 24 hours after death, and then fixed with 10% neutral buffered formalin. Paraffin blocks were made with the following regions; 8 regions from the spinal cord (the levels of the upper cervical segment, the cervical enlargement, the upper thoracic segment, the mid thoracic segment, the lower thoracic segment, the upper lumbar segment, the lumbar enlargement, the sacral segment), 14 regions from the brain stem (the levels of the spinomedullary junction, the pyramidal decussation, the medial lemniscus decussation, the obex, the mid-olivary medulla, the upper medulla, the pontomedullary junction, the lower pons, the mid pons, the upper pons, the isthmus rhombencephali, the inferior colliculus, the superior colliculus, the posterior commissure). Using virtual microscope software, we made digital neuro-slides which can be used anywhere and anytime regardless of equipment of microscope. To help understanding anatomy and functions of nervous tissue, we also made neuro-atlas based on the digital slide images. As results, the outline and detailed structures of nuclei and tracts are easily discriminated and also matched with marks and nomenclatures of neuro-atlas. Moreover, the cytoarchitecture of each nucleus and histological features can be well distinguished. We hope that this product would be used as a useful neuroscience tutorial material for the medical and paramedical school students, clinical trainees like interns and residents, and also neuroscience researchers.

Ectopic Expression of Ephrin-A5 Under the EphA8 Promoter at the Anterior Region of the Superior Colliculus

EphA/ephrin-A mediated signaling has emerged as a key mechanism regulating axon guidance and topographic mapping, particularly in the well-characterized visual system from the retina to the superior colliculus (SC). In this study, EphA8 bacterial artificial chromosome (BAC) was manipulated to contain a floxed eGFP and human ephrin-A5 expression cassette using homologous recombination method. In the mice containing the recombinant BAC, it was shown that GFP is expressed in an anterior>posterior gradient in the SC. Furthermore, when these mice were crossed with the transgenic mice expressing Cre under the EphA8 promoter, it was evident that a GFP expression cassette was eliminated, and that human ephrin-A5 was ectopically expressed in the anterior region of the SC. This transgenic model would be useful to analyze the role of ephrin-A5 in the SC during the retinocollicular topography formation.

Redundancia de la información visual en el condicionamiento aversivo: papel del colículo superior / Redundancy of visual information in aversive conditioning: role of the superior colliculus

Una característica de casi todos los sistemas biológicos es el procesamiento en paralelo o distribuido,el cual otorga al sistema una redundancia funcional que garantiza la permanencia de procesosincluso en ausencia de porciones del sistema. En el sistema visual existen tres vías que simultáneamentese encargan de varios aspectos de la percepción. El procesamiento realizado por la ramacolicular de este sistema está muy relacionado con los sistemas de valoración emocional límbicos,gracias a la vía colículo superior —núcleo suprageniculado— amígdala. En el presente trabajo seevaluó el efecto de la inactivación del colículo superior en la formación de un condicionamientoaversivo visual. Para esto ratas Wistar recibieron una microinyección intracolicular de lidocaína (1%)durante la adquisición del condicionamiento. Los resultados obtenidos mostraron claramente que elcolículo superior no es una estructura indispensable para la formación de tal condicionamiento, loque sugiere que otros sistemas de relevo subcortical deben estar implicados. A partir de ello esposible hipotetizar nuevas formas de aproximación al estudio de las características de redundanciafuncional en el sistema visual.

A relevant feature of biological systems is the distributed processing. This kind of informationprocessing ensures a functional redundancy that allows a functional level even in the absence ofsome regions of the system. In the case of visual system, the parallel processing relies on threesimultaneous pathways, each one of them carrying out certain aspects of visual information processing.The collicular branch of this parallel system is related to emotional aspects. This pathway transmitsinformation from the superior colliculus to the amygdala, via the suprageniculate nucleus. Here wetest the effect of the transient inhibition of the superior colliculus on the acquisition of a classicalaversive conditioning. Wistar rats received an intracollicular microinjection of lidocaine (1%)immediately before the training session. Our results clearly show that the superior colliculus is notthe main structure involved in the acquisition of this kind of associative learning suggesting thecontribution of other subcortical structures.

NMDA receptor blockade alters the intracellular distribution of neuronal nitric oxide synthase in the superficial layers of the rat superior colliculus

Nitric oxide (NO) is a molecular messenger involved in several events of synaptic plasticity in the central nervous system. Ca2+ influx through the N-methyl-D-aspartate receptor (NMDAR) triggers the synthesis of NO by activating the enzyme neuronal nitric oxide synthase (nNOS) in postsynaptic densities. Therefore, NMDAR and nNOS are part of the intricate scenario of postsynaptic densities. In the present study, we hypothesized that the intracellular distribution of nNOS in the neurons of superior colliculus (SC) superficial layers is an NMDAR activity-dependent process. We used osmotic minipumps to promote chronic blockade of the receptors with the pharmacological agent MK-801 in the SC of 7 adult rats. The effective blockade of NMDAR was assessed by changes in the protein level of the immediate early gene NGFI-A, which is a well-known NMDAR activity-dependent expressing transcription factor. Upon chronic infusion of MK-801, a decrease of 47 percent in the number of cells expressing NGFI-A was observed in the SC of treated animals. Additionally, the filled dendritic extent by the histochemical product of nicotinamide adenine di-nucleotide phosphate diaphorase was reduced by 45 percent when compared to the contralateral SC of the same animals and by 64 percent when compared to the SC of control animals. We conclude that the proper intracellular localization of nNOS in the retinorecipient layers of SC depends on NMDAR activation. These results are consistent with the view that the participation of NO in the physiological and plastic events of the central nervous system might be closely related to an NMDAR activity-dependent function.

The Study of in Vivo Visual Pathway Tracing using Magnetic Magnanese Tracer / 의학물리

Purpose: To evaluate the tracing of optic nerve tract using manganese enhanced magnetic resonance imaging. Materials and Methods: After injecting 30 microliter of MnCl2 (1 mol) into the retina of female New Zealand white rabbit, the contrast enhancements at major anatomical structures of optic nerve tract were evaluated by high resolution T1-weighted images 12 hours, 24 hours, and 48 hours after MnCl2 injection using 3D FSPGR (Fast Spoiled Gradient Recalled echo) pulse sequence at 1.5 T clinical MR scanner with high performance gradient system. Also, for quantitative evaluation, the signal-to-noise ratios of circular ROI on anatomical locations were measured. Results: The major structures on the optic nerve tract were enhanced after injecting MnCl2. The structures, which showed enhancement, were right optic nerve, optic chiasm, left optic tract, left lateral geniculate nucleus, left superior colliculus. The structures on the contralateral optic pathway to the right retina were enhanced whereas the structures on the ipsilateral pathway did not show enhancement. Conclusion: The Mn transport through axonal pathway of optic nerve system was non-invasively observed after injecting MnCl2 at the retina, which is the end terminal of optic nerve system. This Mn transport seems to occur by voltage gated calcium (Ca2+) channel and in case of direct injection into the retina, the fast transport pathway of voltage gated calcium channel seems to be responsible for Mn transport.

An intracellular study of pretectal influence on the optic tectum of the frog, Rana catesbeiana / 神经科学通报·英文版

<p><b>OBJECTIVE</b>A few investigations have been reported about pretectal suppressive influences on the optic tectum of frog, but characteristics of tectal activity to pretectal input are left unknown. We made intracellular recordings to demonstrate the unexpected complexity in synaptic mechanisms involved in the suppressive influences of pretecal stimulation on the tectal cells.</p><p><b>METHODS</b>In the present study, we investigated the neuronal activity evoked by pretectal (Lpd/P) nuclei stimulation using intracellular recording technique.</p><p><b>RESULTS</b>The pretectal stimulation mainly elicited two types of responses in the ipsilateral tectum: an excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP) and a pure IPSP. The latter predominated in the tectal cells responding to pretectal stimulation. In a few cells, biphasic hyperpolarization appeared under stronger stimulus intensities. The spikes of tecto-pretectal projecting cells elicited by antidromical stimulation were recorded in the ipsilateral tectum, which revealed reciprocal connections between the tectum and particular pretectal nuclei. The synaptic natures underlying pretecto-tectal information transformation have also been demonstrated. EPSPs with short latencies were concluded to be monosynaptic. Most IPSPs were generated through polysynaptic paths, but monosynaptic IPSPs were also recorded in the tectum. Nearly 98% of impaled tectal cells (except for antidromically projecting cells) showed inhibitory responses to pretectal stimulation.</p><p><b>CONCLUSION</b>The results provide strong evidence that pretectal cells broadly inhibit tectal neurons as that has suggested by behavioral and extracellular recording studies.</p>

Changes of Calretinin-Immunoreactivities in the Rat Superior Collicuclus after Eye Enucleation / 체질인류학회지

Calcium-binding proteins play an important role in the protection, differentiation, and reorganization of the central nervous system. The effects of neonatal retinal deafferentiation on calretinin, and tracing of retinotectal pathway were examined immunohistochemically in the superficial layer of the rat superior colliculus. Tracing with cholera toxin was revealed on the superior colliculus contralateral to the ocular injection. On the contralateral side of superior colliculus, the calretinin-immunoreactive (IR) cells were dramatically increased, calretinin-IR fibers were markedly decreased in the superficial layer. These results show that retinal deafferentation results in an increase of calretinin-immunoreactive cells within the superficial layers of the superior colliculus, which suggest reorganization of neurons in superior colliculus.

Expression of neuronal nitric oxide synthase in the developing superficial layers of the rat superior colliculus

We investigated the level of expression of neuronal nitric oxide synthase (nNOS) in the retinorecipient layers of the rat superior colliculus during early postnatal development. Male and female Lister rats ranging in age between the day of birth (P0) and the fourth postnatal week were used in the present study. Two biochemical methods were used, i.e., in vitro measurement of NOS specific activity by the conversion of [ H]-arginine to [ H]-citrulline, and analysis of Western blotting immunoreactive bands from superior colliculus homogenates. As revealed by Western blotting, very weak immunoreactive bands were observed as early as P0-2, and their intensity increased progressively at least until P21. The analysis of specific activity of NOS showed similar results. There was a progressive increase in enzymatic activity until near the end of the second postnatal week, and a nonsignificant tendency to an increase until the end of the third week was also observed. Thus, these results indicated an increase in the amount of nNOS during the first weeks after birth. Our results confirm and extend previous reports using histochemistry for NADPH-diaphorase and immunocytochemistry for nNOS, which showed a progressive increase in the number of stained cells in the superficial layers during the first two postnatal weeks, reaching an adult pattern at the end of the third week. Furthermore, our results suggested that nNOS is present in an active form in the rat superior colliculus during the period of refinement of the retinocollicular pathway.

Changes of beta-Adrenergic Receptor mRNA in the Visual Cortex and Superior Colliculus of Monocular Deprivated Rat

PURPOSE: To investigate the change of the Beta adrenergic system in the rat visual cortex and superior colliculus after visual deprivation during a critical period of postnatal development. METHODS: The changes of beta 1 and beta 2 adrenergic receptor mRNA were investigated by using northern blot analysis in the rat visual cortex and superior colliculus. The right eyelid of visually deprived rat was sutured at the 10th postnatal days. After visual deprivation for 4 weeks, the rat were sacrificed and the visual cortex and superior colliculus tissues were removed for analysis. RESULTS: Beta 1 and beta 2 adrenergic receptor mRNA expression was decreased in the contralateral visual cortex to the deprived eye. In the superior colliculus, beta 2 adrenergic receptor mRNA expression increased in both sides, but a much greater increase was shown in the ipsilateral superior colliculus than the contralateral side. CONCLUSIONS: These results suggests that visual deprivation during a critical period of postnatal development influences the beta adrenergic system in the rat visual cortex and superior colliculus.

Mutation in rugose gene locus affects the pigment cell number and al ters the optic lobe phenotype in the Drosophila visual system

In this study, the pigment cell number in several ommatidia in rugose mutant eyes were analyzed and showed a multiplication of secondary pigment cells in the null mutation. In addition, rugose mutant-flies exhibited optic lobe defects. The lamina, medulla, lobula and lobula plate were affected by mutation. The results suggested that rugose gene encodes a secondary pigment cell specific function and plays an essential role in determining the optic lobe's structure

Removal of the cortical projections alters expression of NOS in the different cell types of the superficial layers of the superior colliculus in rats

Nitric oxide has several biological roles and nitric oxide synthase (NOS) is expressed in the nervous system, and co-localizes with NADPH-diaphorase. The superficial layers of the superior colliculus (SC), which receive retinal and cortical inputs, present NADPH-d staining in a sub-population of neurons that include all cell types. We have previously shown, by NADPH-diaphorase, that eye enucleation alters the intracellular distribution of NOS. Here, we studied the effect of cortical ablation on NOS expression by neurons in collicular superficial layers. Our results show that cortical ablation alters the proportion of different NOS-positive cell types, but not the intracellular distribution of the enzyme

Differential expression of AMPA-type glutamate receptor subunits during development of the chick optic tectum

Glutamate receptors have been often associated with developmental processes. We used immunohistochemical techniques to evaluate the expression of the AMPA-type glutamate receptor (GluR) subunits in the chick optic tectum (TeO). Chick embryos from the 5th through the 20th embryonic day (E5-E20) and one-day-old (P1) chicks were used. The three types of immunoreactivity evaluated (GluR1, GluR2/3, and GluR4) had different temporal and spatial expression patterns in the several layers of the TeO. The GluR1 subunit first appeared as moderate staining on E7 and then increased on E9. The mature GluR1 pattern included intense staining only in layer 5 of the TeO. The GluR2/3 subunits presented low expression on E5, which became intense on E7. The staining for GluR2/3 changed to very intense on E14 in tectal layer 13. Staining of layer 13 neurons is the most prominent feature of GluR immunoreactivity in the adult TeO. The GluR4 subunit generally presented the lowest expression starting on E7, which was similar to the adult pattern. Some instances of transient expression of GluR subunits were observed in specific cell populations from E9 through E20. These results demonstrate a differential expression of the GluR subunits in the embryonic TeO, adding information about their possible functions in the developmental processes of the visual system

Differential Effects of Aging on NADPH-diaphroase and Tyrosine Hydroxylase-Positive Neurons in Rat Brain Stem / 대한해부학회지

Nitric oxide is synthesized by neurons containing the nitric oxide synthase (NOS), and the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) is a selective histochemical marker for the brain. Although, many reports have been published describing in detail the distribution of NADPH-d and tyrosine hydroxylase (TH), little information is available on possible morphological changes of NADPH-d and TH containing neurons during aging of the brain stem. Therefore, in this study, we assessed the effects of aging on the somal area and staining intensity of NADPH-d-positive and TH-immunoreactive (TH-IR) neurons in rat brain stem. In previous studies, enzyme activities of nitric oxide synthase (NOS) and NADPH-d were shown to be in an almost perfect correlation in the brain. Therefore, we evaluated the change of NADPH-d-positive neurons using a microdensitometrical method as a way of measuring changes in NOS activity. By using a double-labelling technique, we have shown that these two enzymes are located in separate neurons in most brain stem nuclei. In the aged group, the size of NADPH-d-positive neurons was not significantly changed in most nuclei of the brain stem compared to the control group. Staining intensity of NADPH-d-positive neurons was significantly changed in periaqueductal gray, superior colliculus and inferior colliculus in the aged group. In the aged rats, the size of TH-IR neurons was significantly changed in locus ceruleus and lateral paragigantocellular nucleus. Staining intensity of TH-IR neurons was significantly decreased in principal trigeminal nucleus, locus ceruleus and lateral paragigantocellular nucleus of the aged group. These results demonstrate that the NADPH-d-positive and TH-IR neurons are differently influenced by aging than the control group in the brain stem of rats. Difference in the changes of NADPH-d-positive neurons in brain stem nuclei suggest that neuronal NOS is regulated by different mechanims in the regions of the brain stem during aging.

MR Imaging of Pineal Cysts

PURPOSE: To evaluate the incidence and characteristic findings of pineal cyst incidentally detected on magnetic resonance(MR) imaging. MATERIALS AND METHODS: Brain MR images obtained in 2432 patients were retrospectively reviewed to determine the incidence and MR findings of pineal cysts, which were evaluated according to their size, shape, location, signal intensity, interval change, contrast enhancement and mass effect on adjacent structures. RESULTS: Cysts were encountered in 107(4.4 %) of 2432 patients evaluated. Their size ranged from 1 x 1 x 1 to 15 x 8 x 9(mean, 5.97 x 3.87 x 4.82)mm. All were spherical(n=53) or oval(n=54) in shape. Their margin was smooth and they were homogeneous in nature. On T1-weighted images, the cysts were seen to be hyperintense(n=57) or isointense(n=50) to cerebrospinal fluid, but less so than brain parenchyma. T2-weighted images showed them to be isointense(n=51) or hyperintense(n=56) to cerebrospinal fluid. The cysts were centrally located in 65 cases and eccentrically in 42. Compression of the superior colliculi of the tectum was demonstrated in 17 cases(15.9 %). No patients presented clinical symptoms or signs related to either pineal or tectal lesions. Peripheral enhancement around the cyst after Gd-DTPA injection was demonstrated in 51 cases ( 1 00 %). Follow-up examinations in 19 cases demonstrated no interval change. CONCLUSION: The incidence of pineal cysts was 4.4%. The MR characteristics of simple pineal cysts include: (1) an oval or spherical shape, (2) a smooth outer margin and homogeneous nature, (3) isosignal or slightly high signal intensity to cerebrospinal fluid on whole pulse sequences, (4) ring enhancement after contrast injection,(5) an absence of interval change, as seen during follow up MR study. These MR appearances of pineal cysts might be helpful for differentiating them from pineal tumors.

The superior colliculus, a neuronal network resistant to the Gaba withdrawal syndrome

Chronic intracortical perfusion of GABA (Gamma Amino Butyric Acid) and its subsequent withdrawal generates, the GABA withdrawal syndrome (GWS). This particular epileptic model has been observed in the motor cortex of monkeys and rats. Our purpose was to study the GWS in the motor cortex (MC), dorsal hippocampus (DH), and superior colliculus (CS). Thirty chronically-implanted adult Wistar rats were separeted into 3 groups of 10 (8 experimental and 2 controls). The first group received GABA in MC, the second in the DH and the third in the SC. GABA was released in doses of 10 to 60 mug/mul/h for 6 days employing osmotic mini-pumps. Two control rats per group received saline solution in the above-mentioned structures. Rats perfused in the MC showed GWS after interruption of the GABA flow. The group perfused in the DH showed paroxysmal discharges and epileptic seizures during perfusion. They also later showed GWS. No epileptic effects were observed in the SC-perfused group during either the GABA perfusion or during withdrawal. None of the six control animals showed epileptic effects. Our results show that the SC offers a strong resistance to GWS. This could be explained by the particular neuronal network structure of rat SC.

The developmental expression of voltage dependent calcium channel alpha1 subunits (alpha1D, alpha1B, alpha1A, alpha1E) mRNA in the rat brain / 대한해부학회지

Voltage dependent calcium channels (VDCCs) mediate Ca++ influx into cells and are responsible for regulation of a variety of physiological effects. The key functional property of VDCCs are attributed to the calcium-pore forming alpha1 subunit. In this study, distribution pattern of alpha1 subunit (alpha1D, alpha1B, alpha1A, alpha1E) mRNA of VDCCs in developing and adult rat brain was investigated by in situ hybridization histochemistry. In the adult rat brain, each alpha1 subunit mRNA displayed a specific and distinct distribution pattern. alpha1D was highly expressed in the olfactory bulb, dentate gyrus, pituitary gland, pineal gland, hypothalamus, superior colliculus and cerebellum. Relatively low level of alpha1B was expressed throughout the whole brain and strong expression of alpha1A was observed in CA3 area of Ammon's horn, medial geniculate body, inferior colliculus and cerebellum. High level of alpha1E was found in the olfactory bulb, hippocampus, dentate gyrus, medial habenular nucleus and cerebellum. Moreover, alpha1B, alpha1A and alpha1E were expressed only in the nervous system but alpha1D was expressed not only in the nervous system but also in other tissues including liver, heart, lung and skeletal muscle. Generally the expression of alpha1D, alpha1A, and alpha1E subunit was observed from E14 and thereafter the intensity of labeling was gradually increased to P14 and then decreased to the adult level. But the expression of alpha1B subunit was observed from E14 and gradually increased to E20 and P0 and then decresaed. From the differential expressions of VDCC alpha1 subunits in developing and adult rat brain, it is suggested that each type of VDCCs may play a distinct roles in neural and nonneural tissues, and the VDCCs may be related with development of nervous system.

Retrieval of overtrained place navigation during occlusion of one eye and ipsi- or contralateral blockade of relevant brain centers in rats

Place navigation engrams acquired with intact brain can be retrieved with either eye and are stored in both hemispheres. The retrieval circuitry was examined by testing an overtrained rat under lidocaine inactivation of the hippocampus, visual cortex, and superior colliculus. Thirty-three hooded rats with implanted cannulae aimed at the above structures were trained to find a target in the southwest quadrant of the pool. Retrieval was tested during occlusion of one eye alone or combined with ipsi-or contralateral blockade (1 æ4 por ciento lidocaine) of hippocampus, hippocampus and visual cortes, or hippocampus, visual cortex, and superior colliculus. The intact brain escape latencies (9,8 s) were only slightly prolonged by occlusion of one eye (to 12,6 s). Blockade of centers ipsi/ or contralateral to the occluded eye increased escape latencies to 12,7 or 15,2 s for hippocampus, to 16,8 or 16,9 s for hippocampus and visual cortex, and to 23,6 or 17,4 s for hippocampus, visual cortex, and superior colliculus, respectively. Significant asymmetry appearing in the last case indicates that the superior colliculus plays an important role in mediation of the crossed visual input supporting place navigation. Residual goal-finding capacity in rats with blockade of centers ipsilateral to the occluded eye is probably due to uncrossed visual projections to the intact hemisphere