Distribution of calbindin, parvalbumin and calretinin in the lateral geniculate nucleus and superior colliculus in Cebus apella monkeys

We studied the distribution of the calcium-binding proteins calbindin, parvalbumin and calretinin, in the superior colliculus and in the lateral geniculate nucleus of Cebus apella, a diurnal New World monkey. In the superior colliculus, these calcium-binding proteins show different distribution patterns throughout the layers. After reaction for calretinin one observes a heavy staining of the neuropil with few labeled cells in superficial layers, a greater number of large and medium-sized cells in the stratum griseum intermediale, and small neurons in deep layers. The reaction for calbindin revealed a strong staining of neuropil with a large number of small and well stained cells, mainly in the upper half of the stratum griseum superficiale. Intermediate layers were more weakly stained and depicted few neurons. There were few immunopositive cells and little neuropil staining in deep layers. The reaction for parvalbumin showed small and medium-sized neurons in the superficial layers, a predominance of large stellate cells in the stratum griseum intermediale, and medium-sized cells in the deep layers. In the lateral geniculate nucleus of Cebus, parvalbumin is found in the cells of both the P and M pathways, whereas calbindin is mainly found in the interlaminar and S layers, which are part of the third visual pathway. Calretinin was only found in cells located in layer S. This pattern is similar to that observed in Macaca, showing that these calcium-binding proteins reveal different components of the parallel visual pathways both in New and Old World monkeys.     

High- and low-frequency repetitive transcranial magnetic stimulation differentially activates c-Fos and zif268 protein expression in the rat brain

Repetitive transcranial magnetic stimulation (rTMS) has been shown to alter cortical excitability depending on the stimulus-frequency used, with high frequency (5 Hz and higher) increasing it but low frequency (usually 1 Hz or lower) reducing it. To determine the efficiency of different rTMS protocols in inducing cortical network activity, we tested the acute effect of one low-frequency rTMS protocol (1 Hz) and two different high-frequency protocols (10 Hz and intermittent theta-burst stimulation, iTBS) on the expression of the two immediate early gene (IEG) proteins c-Fos and zif268 in the rat brain. The cortical expression of both IEGs was specifically changed in an rTMS-dependent manner. One and 10 Hz rTMS enhanced c-Fos protein expression in all cortical areas tested, while iTBS was effective only in limbic cortices. Zif268 expression was increased in almost all cortical areas after iTBS, while 10 Hz rTMS was effective only in the primary motor and sensory cortices. One Hertz rTMS had no effect on cortical zif268 expression. Furthermore, sham-rTMS had no effect on zif268 expression but increased c-Fos in limbic cortices. This is the first study demonstrating that cortical zif268 and c-Fos expression can be specifically modulated by acute rTMS depending on the pattern of stimulation applied. Authors S. Aydin-Abidin and J. Trippe contributed equally to this work.     

Synaptic development in the rabbit superior colliculus and visual cortex

Summary The development of synapses in the visual cortex (VC) and superior colliculus (SC) of the rabbit has been examined with the electron microscope. In both areas, the number of synapses reaches adult levels by 20–25 days of postnatal age, but the development in the visual cortex is delayed in comparison to that in the superior colliculus. When S synapses (spheroidal vesicles, asymmetric thickening) are compared with F synapses (flattened vesicles, symmetric thickening), even greater differences are seen. In both the VC and SC, S synapses develop earlier than F synapses, though there is considerable overlap. Of interest is the fact that synapses in the visual cortex seem to overshoot their adult levels late in development, suggesting that an excess of synapses may be formed in this system. Multiple synapses, probably of retinal origin, increase in the first 3 weeks of synaptic development in the SC, but never are present in significant proportions in the VC.Synapse formation most often is characterized by formation of a junction and a postsynaptic thickening, followed by acquisition of synaptic vesicles. After 15 days, there is only a small number of such non-vesicle synapses in either the SC or VC.     

Location and distribution of Fos protein expression in rat hippocampus following acute moderate aerobic exercise

Hippocampal neurons are activated during endurance exercise; however, little attention has been given to the location and spatial distribution of these neurons. We have, therefore, used Fos protein expression to identify the location and distribution of hippocampal neurons that become activated during acute moderate aerobic exercise. Adult rats were assigned into trained running (TR), trained nonrunning (TNR), untrained nonrunning (UNR), and cage-bound (CB) groups. Rats in the TR and TNR groups were trained to run, for three 20-min running periods separated by 3 min rest, on a treadmill. Rats in the UNR group spent identical time on a nonactivated treadmill, while rats in the CB group remained in their home cages throughout the training and experimentation. After training to criterion performance for both TR and TNR groups, both groups were rested for 1 day. Rats in the TR were then run on the treadmill to criterion level, while those in TNR and UNR groups spent equivalent time on the nonactivated treadmill. Animals in all groups were then killed and their brains removed, sectioned, and processed for Fos protein immunocytochemistry. Fos-like immunoreactive (FLI) neurons were counted in the dentate and CA1-3 fields of the hippocampus. The total numbers of hippocampal FLI neurons, as well as FLI neurons in each hippocampal region, were compared among groups. The total numbers of FLI neurons in the hippocampus, as well as in individual regions, were significantly greater in the TR group compared with the other three groups. Similarly, significant differences were found between the TNR group when compared with UNR and CB groups. Conversely, a significant difference existed between UNR and CB only in the CA1 field, which may account for the significant difference in the total number of hippocampal FLI neurons between these two groups. These results show that Fos induction occurs in the hippocampus during moderate physical exercise. Furthermore, the importance of the incorporation of adequate controls to account for possible differences in expression of immediate early gene expression due to trained performing, trained nonperforming, and untrained groups is discussed. The results indicate that adequate control for nonexercise stimuli is necessary for studies of the effect of exercise on the brain when expression of immediate early genes such as c-fos is used as an outcome measure.     

Parvalbumin-like immunostaining in the cat inferior colliculus. Light and electron microscopic investigation

The presence of the calcium-binding protein parvalbumin (PV) was studied in neuronal elements of the cat's inferior colliculus (IC) by means of light and electron microscopic immunocytochemistry. Immunostaining of PV was detected in all three main parts of the IC. Several subtypes of large neurons that differed in size and shape were immunostained, comprising approx. 15% of the total number of PV-containing neurons. Approx. half of the labeled neurons were medium sized. Two types of small neurons were found to be PV synthesizing, and comprised approx. 35% of the total PV-containing population. Ultrastructurally, many dendrites were heavily immunolabeled, and the reaction product was present in dendritic spines as well. Several types of synaptic boutons contained reaction product, and terminated on both labeled and unlabeled postsynaptic targets forming asymmetric and symmetric synapses. Approx. 70% of all PV-immunolabeled terminals contained round synaptic vesicles and formed asymmetric synapses. The majority of these boutons were of the "large round" type and corresponded to the terminals of cochlear nuclei. A lower number were of the "small round" type, and were probably corticotectal terminals. The remaining 30% of PV-containing terminals contained pleomorphic or elongated vesicles and formed symmetric synapses. These terminals corresponded with "P" and "F1" bouton types. Part of these boutons appeared to arise from nuclei of the lateral lemniscus and the superior olive, and a certain percentage likely represented endings of inhibitory interneurons.     

Fos-related protein expression in the midline paraventricular nucleus of the rat thalamus: basal oscillation and relationship with limbic efferents

The expression of Fos-related protein, encoded by the proto-oncogene c-fos, was investigated by means of immunohistochemistry in the paraventricular nucleus of the thalamic midline (PV) during nighttime and daytime in rats entrained to a 12-h light/12-h dark cycle. In the first step of this study the animal's physiological state preceding perfusion was monitored with electroencephalographic recording. It was thus detected that the PV contained a considerable number of Fos-like-immunostained neurons during the hours of darkness, when the rats had been awake, and that the number of Fos-like-immunoreactive neurons was significantly lower during the hours of light, after a period of sleep. In the second step of this study Fos immunohistochemistry was combined with the retrograde transport of a gold-labeled tracer injected either in the amygdala or in the nucleus accumbens. This strategy enabled us to determine that in the rats perfused during nighttime Fos-related protein was spontaneously induced in PV cells projecting to these targets, with a significant prevalence of neurons projecting to the amygdala in the anterior portion of the PV and of neurons projecting to the nucleus accumbens in the posterior part of the nucleus. In addition, a significant reduction of Fos-like-immunoreactive cells was detected in the PV ipsilaterally to the injection, indicating that tracer administration and axonal transport may interfere with c-fos expression in neurons. Altogether the present data indicate that Fos-related protein expression undergoes a marked oscillation in the PV during 24 h in basal conditions, and that c-fos is induced in the PV relay neuronal subsets when the animal is awake. This study suggests that the thalamic midline represents a site of circadian changes in neuronal genomic expression and that this information is conveyed to limbic and limbic-related structures.On leave from the Department of Anatomy, Hunan Medical University, Changsha, Hunan, People's Republic of China     

The distribution of calbindin, calretinin and parvalbumin immunoreactivity in the human thalamus

Calcium-binding proteins show a heterogeneous distribution in the mammalian central nervous system and are useful markers for identifying neuronal populations. The distribution of the three major calcium-binding proteins - calbindin-D28k (calbindin), calretinin and parvalbumin - has been investigated in eight neurologically normal human thalami using standard immunohistochemical techniques. Most thalamic nuclei show immunoreactive cell bodies for at least two of the three calcium-binding proteins; the only nucleus showing immunoreactivity for one calcium-binding protein is the centre médian nucleus (CM) which is parvalbumin-positive. Overall, the calcium-binding proteins show a complementary staining pattern in the human thalamus. In general terms, the highest density of parvalbumin staining is in the component nuclei of the ventral nuclear group (i.e. in the ventral anterior, ventral lateral and ventral posterior nuclear complexes) and in the medial and lateral geniculate nuclear groups. Moderate densities of parvalbumin staining are also present in regions of the mediodorsal nucleus (MD). By contrast, calbindin and calretinin immunoreactivity both show a similar distribution of dense staining in the thalamus which appears to complement the pattern of intense parvalbumin staining. That is, calbindin and calretinin staining is most dense in the rostral intralaminar nuclear group and in the patchy regions of the MD which show very low levels of parvalbumin staining. However, calbindin and calretinin also show low levels of staining in the ventral nuclear complex and in the medial and lateral geniculate bodies which overlaps with the intense parvalbumin staining in these regions. These results show that the calcium-binding proteins are heterogeneously distributed in a complementary fashion within the nuclei of the human thalamus. They provide further support for the concept recently proposed by Jones (Jones, E.G., 1998. Viewpoint: the core and matrix of thalamic organization. Neuroscience 85, 331-345) that the primate thalamus comprises of a matrix of calbindin immunoreactive cells and a superimposed core of parvalbumin immunoreactive cells which may have differential patterns of cortical projections.     

Light‐dependent retinal innervation of the rat superior colliculus

Mammalian retinal projections are divided into two anatomically and functionally distinct systems: the primary visual system, which mediates conscious visual processing, and the subcortical visual system, which mediates nonconscious responses to light. Light deprivation during a critical period in development alters the anatomy, physiology, and function of the primary visual system in many mammalian species. However, little is known about the influence of dark‐rearing on the development of the subcortical visual system. To evaluate whether the early lighting environment alters the anatomy of the subcortical visual system, we examined the retinas and retinofugal projections of rats reared in a 12:12 light/dark cycle or in constant dark from birth to 4 months of age. We found that dark‐rearing was associated with a reduction in the distribution of retinal fibers in the stratum opticum of the contralateral superior colliculus. In contrast to the plasticity of the retinocollicular projection, retinal input to sleep, circadian, and pupillary control centers in the hypothalamus, pretectum, and lateral geniculate complex was unaffected by dark‐rearing. A decrease in retinal innervation of the stratum opticum and intermediate layers of the superior colliculus may account for some of the deficits in multisensory integration that have been observed in dark‐reared animals of several species. Anat Rec 2007. © 2007 Wiley‐Liss, Inc.     

Stimulus frequency affects c-fos expression in the rat visual system

We have characterised the c-fos expression patterns in various centers of the visual pathway of adult rats monocularly stimulated either by continuous or flickering light at different frequencies. Results show different immunocytochemical patterns in all centers studied, the geniculate lateral complex (LGC), superior colliculus (SC) and primary visual cortex (Oc1), depending on the physical characteristics of the stimulus (blinking frequency and light wavelength). After stimulation of the left eye, the ipsilateral pathway presents a substantial density of immunoresponsive cells, which is greater than expected with respect to the number of fibers that project ipsilaterally from the retina to the LGC and the superficial layers of the SC. A surprisingly high positive immunoresponsiveness is obtained in all cases with coherent light stimulation in the red spectrum (634 nm).     

Subcellular localization of neuronal nitric oxide synthase in the superficial gray layer of the rat superior colliculus

The superficial layers of the rat superior colliculus (sSC) receive innervation from retina and include nitric oxide synthase (NOS)-immunoreactive neurons. We used electron microscopic immunocytochemistry to assess the subcellular localization of neuronal NOS (nNOS) in the sSC. nNOS immunoreactivity was detected on the external membrane of mitochondria, endoplasmic reticulum, in pre- and postsynaptic profiles and also diffusely distributed in the cytosol. Postsynaptic labeled regions were often associated with presumptive retinal unlabeled terminals. Microtubules also appeared intensely labeled. These results show that NOS immunoreactive neurons may be innervated by retinal terminals and suggest an association of nNOS with cytoskeletal elements.     

Synaptic patterns in the superficial layers of the superior colliculus of the monkey,Macaca mulatta

Summary While the synaptic patterns studied with the electron microscope in the upper layers of the superior colliculus of the monkey are basically similar to those described for the rat, there are notable differences in the terminal patterns of the afferent pathways.The retinotectal pathway in monkeys terminates sparsely near the surface in the caudal part of the colliculus. Most of the terminals undergo an electron dense reaction in degeneration and are rapidly removed from their postsynaptic sites.The corticotectal pathway terminates heavily throughout superficial layers making both axodendritic and serial synaptic connections. The terminals undergo neurofilamentous and dense degenerative reactions.It is suggested from a comparison of the retinotectal and retinogeniculate pathways that terminals which undergo the neurofilamentous degenerative reaction belong to a different population of axons from those undergoing only the dense reaction.     

Time of origin of neurons of the rat superior colliculus in relation to other components of the visual and visuomotor pathways

Summary Groups of pregnant rats were injected with two successive daily doses of ³H-thymidine from gestational day 12 and 13 (E12+E13) until the day before parturition (E21+22) in order to label all the multiplying precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labelled) on specific days was determined in the separate layers of the superior colliculus. Neurogenesis begins with the production of a few large multipolar neurons in layers V and IV on day E12; the bulk (87%) of these cells are generated on day E13. This early-produced band of large neurons, the intermediate magnocellular zone, divides the superior colliculus into two cytogenetically distinct regions. In both the deep and the superficial superior colliculus neuron production is relatively protracted. In the deep superior colliculus neuron production peaks on day E15 in layer VII, on day E15 and E16 in layer VI, and on day E16 (the large neurons excluded) in layer V, indicating an inside-out sequence. In the superficial superior colliculus peak production time of layer III cells is on day E15 and of layer IV cells on day E16; peak production time of both layer I and II is on day E16 but in the latter region neuron production is more prolonged and ends on day El8. One interpretation of these results is that the two pairs of superficial layers are produced in an outside-in sequence. These three cytogenetic subdivisions of the superior colliculus may be correlated with its structural-functional parcellation into an efferent spinotectal, a deep somatomotor and a superficial visual component.A comparison of neurogenesis in different components of the visuomotor and visual pathways of the rat indicates that the motor neurons of the extraocular muscles, the abducens, trochlear and oculomotor nuclei, and neurons of the nucleus of Darkschewitsch are produced first. Next in line are source neurons of efferents to the bulb and the spinal cord: those of the Edinger-Westphal nucleus and the intermediate magnocellular zone of the superior colliculus. These are followed by the relay neurons of the dorsal nucleus of the lateral geniculate body. The neurons of the superficial superior colliculus and of the visual cortex implicated in visual sensori-motor integrations are produced last.Abbreviations A aqueduct - ap stratum album profundum (layer VII) - bi brachium of the inferior colliculus - c caudal - CGd central gray, pars dorsalis - CGl central gray, pars lateralis - CGv central gray, pars ventralis - dm deep magnocellular zone - EW Edinger-Westphal nucleus - gi stratum griseum intermediale (layer IV) - gp stratum griseum profundum (layer VI) - gs stratum griseum superficiale (layer II) - IC inferior colliculus - im intermediate magnocellular zone - LGd lateral geniculate nucleus, pars dorsalis - ll lateral lemniscus - lm stratum lemnisci (layer V) - MG medial geniculate nucleus - ND nucleus of Darkschewitsch - NO nucleus of the optic tract - op stratum opticum (layer III) - ot optic tract - r rostral - SC superior colliculus - vIII third ventricle - ZO stratum zonale (layer I) - III oculomotor nucleus - IV trochlear nucleus - Vm mesencephalic nucleus of the trigeminal - VI abducens nucleus     

The neuropil in superficial layers of the superior colliculus of the mouse

Summary In a study of Golgi preparations of the superior colliculus of the mouse, three fundamental types of neurons are described. These are: horizontal cells located in the stratum zonale, short axon cells abundant in the stratum griseum superficiale, and long projecting neurons for which representative types are described in the stratum opticum. In the electron microscope these three types of cells are recognized. Peculiar collateral dendritic processes of horizontal cells and of some short axon cells are correlated in Golgi and electron microscope images. They are identified as vesicle-containing dendritic processes. Electron microscopy of the neuropil in the stratum griseum superficiale shows the existence of three major categories of vesicle-containing processes that have been identified as optic terminals, vesicle-filled dendritic profiles of short axon cells and terminals with small vesicles. Their synaptic relations are studied in normal preparations and in experimental animals after eye enucleation and cortical lesions.Supported by research grant from Fundación Eugenio Rodríguez Pascual.     

Postnatal development of the superficial layers in the rat superior colliculus: a study with Golgi-Cox and Klüver-Barrera techniques

Summary The postnatal development of the superficial (optic) layers of the rat superior colliculus has been studied using Klüver-Barrera staining and Golgi impregnation in rats aged 3–45 days. The Klüver-Barrera staining reveals that the SC of 3 day old rats is morphologically immature with no obvious lamination. It contains densely packed cells of uniform size. The packing density of the cells gradually decreases between 9 and 15 days as the thickness of the layers increases. The first myelinated fibres in the SC appear at 15 days but the stratum opticum is still not recognizable. By 30 days, the SC has a distinctly laminated appearance, but the thickness of the superficial layers continues to increase until day 45 postnatal. Golgi-Cox impregnation displays the range of neuronal types in the superficial layers of the SC previously described by Langer and Lund (1974). Using the morphological criteria of these authors for classification of the neurons, the developmental changes of the marginal cells, horizontal cells, ganglion cells types I, II, III and stellate cells have been followed. The SC of 3 day old rats contains immature neurons; only a few larger cells have branched dendrites. In 9 days old SC the neuronal types present in the adult are recognizable, although their appearances are still immature. By 15 days neurons have adult-looking dendritic trees but dendritic growth continues beyond 30 days. The visual part of the SC has a protracted period of postnatal development, the sequence of developmental changes being similar for the different types of collicular neurons. Features common to development are the increasing size of neuronal somata, the increasing length of dendrites and the acquisition of a complex pattern of dendritic arborization. Larger cells appear to commence development earlier than small cells, although the rate of developmental changes is different for each of the various types of collicular neurons.     

Developmental changes in NMDA receptor-mediated visual activity in the rat superior colliculus, and the effect of dark rearing

N-methyl-D-aspartate (NMDA) receptor-mediated activity is considered important for experience-dependent plasticity in the developing visual system. We investigated the influence of age and experience on the role of NMDA receptors in the visual transmission in the superficial grey layer of the superior colliculus (SGS) of the superior colliculus, where, in the adult, NMDA receptors mediate a substantial part of the visual response. In normally reared (postnatal day 14, P14, to adult) rats, visual responses were challenged with NMDA receptor-selective iontophoretic applications of the antagonist D-2-amino-5-phosphonovalerate (AP5). After eye opening (at P14), there was a significant increase in the number of neurones whose visual responses were reduced during AP5 ejection, which peaked at P22 (85%; n = 21), and then declined to adult levels (66%; n = 47) at P25. The mean reduction of the response (from control levels) by AP5 was similar at all ages (approximately 40%). Dark rearing had striking effects on the role of NMDA receptors in visual transmission, especially when comparisons were made between age-matched subjects greater than P25. In these subjects, AP5 ejection reduced the visual responses of all neurones studied. In addition, AP5 ejection caused a significantly larger reduction of visual responses in dark-reared rats (mean reduction 62 ± 4; n = 29) compared with age-matched controls (mean reduction 44 ± 8; n = 23). The D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) reduced the visual responses of every neurone studied and there were no age- or experience-dependent effects. We conclude that NMDA receptors, but not AMPA receptors, assume greater importance for visual transmission in the SGS of dark-reared rats. Received: 2 May 1997 / Accepted: 19 November 1997     

Immediate-early genes in spontaneous wakefulness and sleep: expression of c-fos and NGFI-A mRNA and protein

SUMMARY  We have recently shown that the expression of two immediate-early genes, c-fos and NGFI-A, is strongly affected by sleep deprivation. In this work, we investigated c-fos and NGFI-A expression after periods of spontaneous wakefulness or sleep. We used in situ hybridization and immunocytochemistry to detect the corresponding mRNA and protein levels, respectively. A first group of rats (S-L) was sacrificed during the light hours at the end of a long period of sleep. A second group (W-L) was sacrificed under similar conditions, except that during the last half hour the animals had been spontaneously awake. A third group (W-D) was sacrificed during the dark hours after a long period of continuous wakefulness. We found that c-fos and NGFI-A expression in several brain areas was increased in W-L and W-D rats with respect to S-L rats. Some of these areas, including the cerebral cortex, basal ganglia, and colliculi, may have been activated by the increased sensory and motor activity associated with waking. The activation of other areas, such as the medial preoptic area of the hypothalamus and some brainstem nuclei, may be more directly related to sleep regulation. These results indicate that many regions showing an increased expression of immediate early genes after wakefulness induced by sleep deprivation are also activated by periods of spontaneous wakefulness.     

Enhanced c-Fos expression in superior colliculus,paraventricular thalamus and septum during learning of cue-reward association

Reward-mediated associative learning is important for recognizing the significance of environmental cues. Such learning involves convergence of multimodal sensory inputs with circuits involved in affective and memory processes. Dopamine-dependent plasticity in the striatum plays a pivotal role, but the wider circuits engaged in cue-reward association are poorly understood. To identify candidate structures that may be of particular interest for further detailed electrophysiological and functional analysis, we quantified c-Fos expression in a selection of brain structures. c-Fos is a well-known marker of cell activation with additional potential importance for synaptic plasticity. We compared c-Fos expression between animals exposed to 100 pairings of a novel conditioned stimulus with a subsequent reward, and control animals exposed to the same number of cues and rewards, but where the cues and rewards occurred at random with respect to each other. We found significant increases in c-Fos expression in the superior colliculus in the group exposed to cue-reward pairing. This is consistent with previous recordings in conscious animals, showing modulation of phasic visual responses of single collicular neurons depending on their association with reward. Further, the data also suggest the possibility that the thalamic paraventricular nucleus and septal nuclei may be selectively activated during cue-reward association learning. Little is known of the neurophysiological responses in these structures during such tasks, so the present results suggest they would be targets of interest for future single-neuron recording experiments, designed to confirm whether the neurons show learning-specific modulation.     

Changes induced in the representation of auditory space in the superior colliculus by rearing ferrets with binocular eyelid suture

There have been conflicting reports concerning the importance of visual experience in the development of auditory localization mechanisms. We have examined the representation of auditory space in the superior colliculus of adult ferrets that were visually deprived by binocular eyelid suture from postnatal days 25–28, prior to natural eye opening, until the time of recording. This procedure attenuated the transmission of light by a factor of at least 20–25 and blurred the image so that, as long as the eyelids were still fused, the responses of visual units in the superficial layers of the superior colliculus were labile and very poorly tuned. After the eyelids were opened, the representation of the visual field in these layers appeared to be normal. Acoustically responsive units were, as usual, almost exclusively restricted to the deeper layers of the superior colliculus. However, unlike normal animals, where responses occurring only at stimulus onset pre-dominate, most of these units exhibited sustained or multi-peaked discharge patterns. The degree of spatial tuning of individual units recorded from the normal and deprived groups of animals was not significantly different in either azimuth or elevation. Normally orientated maps of both sound azimuth and elevation were also found in the visually deprived ferrets. However, abnormalities were present in the topography and precision of these representations and consequently in their alignment with the overlying visual map. In particular, an increase was observed in the proportion of auditory units with spatially ambiguous receptive fields, in which the maximum response occurred at two distinct locations. These results indicate that patterned visual experience is not required for establishing at least a crude map of auditory space in the superior colliculus, but suggest that it may play a role in refining this representation during development.