Patterns of connections between zona incerta and brainstem in rats

To understand better the organisation of zona incerta of the thalamus, this study has examined the patterns of connections that this nucleus has with various nuclei of the brainstem. Injections of biotinylated dextran or cholera toxin subunit B were made into the dorsal raphe, midbrain reticular nucleus, pedunculopontine tegmental nucleus, periaqueductal grey matter, pontine reticular nucleus, substantia nigra, superior colliculus, and ventral tegmental area of Sprague-Dawley rats, and their brains were processed by using standard tracer-detection methods. In general, our results show that zona incerta forms the major zone in the thalamus where these ascending brainstem axons terminate and from which descending axons that travel back to these same brainstem centres originate. These incertal inputs and outputs are limited largely to a distinct sector of zona incerta, the dorsal sector. An exception to this pattern is evident in the incertal projection to the deep layers of the superior colliculus; this projection, unlike all of the others, arises from cells in the ventral sector of zona incerta. Our results also show little evidence for a well-defined topography of projection between the brainstem and the zona incerta. For instance, small injections into each brainstem nucleus result in labelled terminals and in cells spread throughout much of the dorsal sector of zona incerta, with no local zone of concentration within the sector. Again, an exception to this pattern is seen in the incertal projection to the superior colliculus. This projection, unlike the others, shows a clear topographical organisation: A medial-lateral shift in the injection site in the colliculus results in a lateral-medial shift in the position of labelled cells in zona incerta. Curiously, even though the incertal projection to the colliculus appears to be mapped, the collicular projection back to zona incerta is not mapped. In conclusion, then, a number of brainstem nuclei (except for the deep collicular layers) have strong and overlapping connections within the same sector of zona incerta. This convergence of many functionally diverse brainstem afferents within zona incerta places this nucleus in a strategic position to sample the general activity of the brainstem and, perhaps, acts as a relay of this information to higher centres, such as the dorsal thalamic relay nuclei and the cerebral hemispheres.     

Fixation cells in monkey superior colliculus. I. Characteristics of cell discharge

1. We studied the role of the superior colliculus (SC) in the control of visual fixation by recording from cells in the rostral pole of the SC in awake monkeys that were trained to perform fixation and saccade tasks. 2. We identified a subset of neurons in three monkeys that we refer to as fixation cells. These cells increased their tonic discharge rate when the monkey actively fixated a visible target spot to obtain a reward. This sustained activity persisted when the visual stimulation of the target spot was momentarily removed but the monkey was required to continue fixation. 3. The fixation cells were in the rostral pole of the SC. As the electrode descended through the SC, we encountered visual cells with foveal and parafoveal receptive fields most superficially, saccade-related burst cells with parafoveal movement fields below these visual cells, and fixation cells below the burst cells. From this sequence in depth, the fixation cells appeared to be centered in the deeper reaches of the intermediate layers, and this was confirmed by small marking lesions identified histologically. 4. During saccades, the tonically active fixation cells showed a pause in their rate of discharge. The duration of this pause was correlated to the duration of the saccade. Many cells did not decrease their discharge rate for small-amplitude contraversive saccades. 5. The saccade-related pause in fixation cell discharge always began before the onset of the saccade. The mean time from pause onset to saccade onset for contraversive saccades and ipsiversive saccades was 36.2 and 33.0 ms, respectively. Most fixation cells were reactivated before the end of contraversive saccades. The mean time from saccade terminatioN to pause end was -2.6 ms for contraversive saccades and 9.9 ms for ipsiversive saccades. The end of the saccade-related pause in fixation cell discharge was more tightly correlated to saccade termination, than pause onset was to saccade onset. 6. After the saccade-related pause in discharge, many fixation cells showed an increased discharge rate exceeding that before the pause. This increased postsaccadic discharge rate persisted for several hundred milliseconds. 7. The discharge rate of fixation cells was not consistently altered when the monkey actively fixated targets requiring different orbital positions. 8. Fixation cells discharged during smooth pursuit eye movements as they did during fixation. They maintained a steady tonic discharge during pursuit at different speeds and in different directions, provided the monkey looked at the moving target.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lateral inhibitory interactions in the intermediate layers of the monkey superior colliculus

The intermediate layers of the monkey superior colliculus (SC) contain neurons the discharges of which are modulated by visual fixation and saccadic eye movements. Fixation neurons, located in the rostral pole of the SC, discharge action potentials tonically during visual fixation and pause for most saccades. Saccade neurons, located throughout the remainder of the intermediate layers of the SC, discharge action potentials for saccades to a restricted region of the visual field. We defined the fixation zone as that region of the rostral SC containing fixation neurons and the saccade zone as the remainder of the SC. It recently has been hypothesized that a network of local inhibitory interneurons may help shape the reciprocal discharge pattern of fixation and saccade neurons. To test this hypothesis, we combined extracellular recording and microstimulation techniques in awake monkeys trained to perform oculomotor paradigms that enabled us to classify collicular fixation and saccade neurons. Microstimulation was used to electrically activate the fixation and saccade zones of the ipsilateral and contralateral SC to test for inhibitory and excitatory inputs onto fixation and saccade neurons. Saccade neurons were inhibited at short latencies following electrical stimulation of either the ipsilateral (1-5 ms) or contralateral (2-7 ms) fixation or saccade zones. Fixation neurons were inhibited 1-4 ms after electrical stimulation of the ipsilateral saccade zone. Stimulation of the contralateral saccade zone led to much weaker inhibition of fixation neurons. Stimulation of the contralateral fixation zone led to short-latency (1-2 ms) excitation of fixation neurons. Only a small percentage of saccade and fixation neurons were activated by the electrical stimulation (latency: 0.5-2.0 ms). These responses were confirmed as either orthodromic or antidromic responses using collision testing. The results suggest that a local network of inhibitory interneurons may help shape not only the reciprocal discharge pattern of fixation and saccade neurons but also permit lateral interactions between all regions of the ipsilateral and contralateral SC. These interactions therefore may be critical for maintaining stable visual fixation, suppressing unwanted saccades, and initiating saccadic eye movements to targets of interest.     

Express saccades elicited during visual scan in the monkey

Monkeys trained to saccade to visual targets can develop separate "express" and "regular" modes in their distribution of saccadic latencies. The purpose of this study was to determine whether this occurs under more natural viewing conditions, when targets are suddenly presented in a structured visual field during visual scan. It was found that scanning saccades stopped appearing 60 msec after a target's onset, and subsequent saccades, which were directed toward the suddenly appearing target, had a bimodal distribution of latencies. Express saccades were more likely to occur as the target was presented later in a fixation. Regular mode saccades were more likely to occur with longer target durations. Scanning saccades made to stimuli of the structured visual field always had unimodal inter-saccadic interval distributions. All these effects were apparent after only 2-3 days of training. These findings, taken together with recent physiological results, suggest that the visuomotor cells of the superior colliculus mediate latency bimodality.     

Estimation of spatiotemporal neural activity using radial basis function networks

We report a method using radial basis function (RBF) networks to estimate the time evolution of population activity in topologically organized neural structures from single-neuron recordings. This is an important problem in neuroscience research, as such estimates may provide insights into systems-level function of these structures. Since single-unit neural data tends to be unevenly sampled and highly variable under similar behavioral conditions, obtaining such estimates is a difficult task. In particular, a class of cells in the superior colliculus called buildup neurons can have very narrow regions of saccade vectors for which they discharge at high rates but very large surround regions over which they discharge at low, but not zero, levels. Estimating the dynamic movement fields for these cells for two spatial dimensions at closely spaced timed intervals is a difficult problem, and no general method has been described that can be applied to all buildup cells. Estimation of individual collicular cells' spatiotemporal movement fields is a prerequisite for obtaining reliable two-dimensional estimates of the population activity on the collicular motor map during saccades. Therefore, we have developed several computational-geometry-based algorithms that regularize the data before computing a surface estimation using RBF networks. The method is then expanded to the problem of estimating simultaneous spatiotemporal activity occurring across the superior colliculus during a single movement (the inverse problem). In principle, this methodology could be applied to any neural structure with a regular, two-dimensional organization, provided a sufficient spatial distribution of sampled neurons is available.     

Target Size Modulates Saccadic Eye Movements in Humans.

The authors investigated mechanisms involved in transformation of spatially extended targets into saccadic eye-movement vectors. Human subjects performed horizontal saccades to targets of varying diameter, which contained no conspicuous elements within the target shape. With increasing target size, express saccades and saccades with fast regular latencies decreased in frequency, whereas frequency of saccades with slow regular latencies increased. For all targets, saccade amplitude distributions showed a peak close to the geometric center of the targets. However, with large targets, increased scatter of saccade amplitudes and increased undershoot of the target center was observed. These effects may reflect distinct subprocesses involved in sensorimotor transformation to spatially extended targets, and may result from modulation of neuronal activity in the superior colliculus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurotrophins and the neuroendocrine brain: different neurotrophins sustain anatomically and functionally segregated subsets of hypothalamic dopaminergic neurons

Hypothalamic neurons control a variety of important hormonal and behavioral functions. Little is known, however, about the neurotrophic factors that these neurons may require for survival and/or maintenance of their differentiated functions. We conducted experiments to examine this issue, utilizing a combination of immunohistochemical, in situ hybridization and cell culture approaches. We found that the low affinity receptor for nerve growth factor (p75 NGFR) is present in small subsets of hypothalamic peptidergic neurons identified as such by their content of galanin, luteinizing hormone-releasing hormone (LHRH) and vasointestinal peptide (VIP). More prominently, however, examination of hypothalamic dopaminergic (DA) neurons for the presence of p75 NGFR-like immunoreactivity revealed that the receptor was present on tyrosine hydroxylase (TH)-positive neurons of the zona incerta and periventricular region, but not on neuroendocrine DA neurons of the tuberoinfundibular region. In situ hybridization experiments using a p75 NGFR cRNA confirmed this distribution. Regardless of the presence or absence of p75 NGFR, neither DA group expresses trkA mRNA, indicating that these two major hypothalamic subsets of DNA neurons are NGF-insensitive. A substantial fraction of TH mRNA-positive cells in the zona incerta expresses trkB mRNA, which encodes the receptor for brain derived neurotrophic factor (BDNF); in turn BDNF supports the in vitro survival of hypothalamic TH neurons bearing p75-NGFR, suggesting that BDNF is trophic for DNA neurons of the zona incerta. In contrast, tuberoinfundibular DA neurons do not express trkB mRNA, but some have trkC mRNA, which encodes the receptor for neurotrophin-3 (NT-3). The in vitro survival of TH neurons devoid of p75-NGFR is supported by NT-3, implying that NT-3 may be trophic for a subset of tuberoinfundibular DA neurons. These results suggest that, in spite of expressing an identical neurotransmitter phenotype, anatomically and functionally segregated DA neurons of the neurodendocrine brain are sustained by different neurotrophic factors.     

Modulation of neuronal activity by target uncertainty

Visual scenes are composed of many elements and although we can appreciate a scene as a whole, we can only move our eyes to one element of the scene at a time. As visual scenes become more complex, the number of potential targets in the scene increases, and the uncertainty that any particular one will be selected for an eye movement also increases. How motor systems accommodate this target uncertainty remains unknown. The activities of neurons in both the cerebral cortex and superior colliculus are modulated by this selection process. We reasoned that activity associated with target uncertainty should be evident in the saccadic motor system at the final stages of neural processing, in the superior colliculus. By systematically changing the number of stimuli from which a selection must be made and recording from superior colliculus neurons, we found that as the target uncertainty increased, the neural activity preceding target selection decreased. These results indicate that neurons within the final common pathway for movement generation are active well in advance of the selection of a particular movement. This early activity varies with the probability that a particular movement will be selected.     

Effects of focal inactivation of dorsal or ventral layers of the lateral geniculate nucleus on cats' ability to see and fixate small targets

To reveal contributions of different subdivisions of the lateral geniculate nucleus (LGN) to visuomotor behavior, segments of either layer A or the C layers were inactivated with microinjections of gamma-aminobutyric acid while cats made saccades to retinally stabilized spots of light placed either in affected regions of visual space or mirror-symmetric locations in the opposite hemifield. Inactivating layer A reduced the success rate for saccades to targets presented in affected locations from 82.4 to 26.8% while having no effect on saccades to the control hemifield. Saccades to affected sites had reduced accuracy and longer initiation latency and tended to be hypometric. In contrast, inactivating C layers did not affect performance. Data from all conditions fell along the same saccade velocity/amplitude function ("main sequence"), suggesting that LGN inactivations cause localization deficits, but do not interfere with saccade dynamics. Cerebral cortex is the only target of the A layers, so behavioral decrements caused by inactivating layer A must be related to changes in cortical activity. Inactivating layer A substantially reduces the activity of large subsets of corticotectal cells in areas 17 and 18, whereas few corticotectal cells depend on C layers for visually driven activity. The parallels between these behavioral and electrophysiological data along with the central role of the superior colliculus in saccadic eye movements suggests that the corticotectal pathway is involved in both deficits and remaining capacities resulting from blockade of layer A.     

New mechanism that accounts for position sensitivity of saccades evoked in response to stimulation of superior colliculus

New mechanism that accounts for position sensitivity of saccades evoked in response to stimulation of superior colliculus. J. Neurophysiol. 80: 3373-3379, 1998. Electrical stimulation of the feline superior colliculus (SC) is known to evoke saccades whose size depends on the site stimulated (the "characteristic vector" of evoked saccades) and the initial position of the eyes. Similar stimuli were recently shown to produce slow drifts that are presumably caused by relatively direct projections of the SC onto extraocular motoneurons. Both slow and fast evoked eye movements are similarly affected by the initial position of the eyes, despite their dissimilar metrics, kinematics, and anatomic substrates. We tested the hypothesis that the position sensitivity of evoked saccades is due to the superposition of largely position-invariant saccades and position-dependent slow drifts. We show that such a mechanism can account for the fact that the position sensitivity of evoked saccades increases together with the size of their characteristic vector. Consistent with it, the position sensitivity of saccades drops considerably when the contribution of slow drifts is minimal as, for example, when there is no overlap between evoked saccades and short-duration trains of high-frequency stimuli.     

The ventral lateral geniculate nucleus and the intergeniculate leaflet: interrelated structures in the visual and circadian systems

The ventral lateral geniculate nucleus (vLGN) and the intergeniculate leaflet (IGL) are retinorecipient subcortical nuclei. This paper attempts a comprehensive summary of research on these thalamic areas, drawing on anatomical, electrophysiological, and behavioral studies. From the current perspective, the vLGN and IGL appear closely linked, in that they share many neurochemicals, projections, and physiological properties. Neurochemicals commonly reported in the vLGN and IGL are neuropeptide Y, GABA, enkephalin, and nitric oxide synthase (localized in cells) and serotonin, acetylcholine, histamine, dopamine and noradrenalin (localized in fibers). Afferent and efferent connections are also similar, with both areas commonly receiving input from the retina, locus coreuleus, and raphe, having reciprocal connections with superior colliculus, pretectum and hypothalamus, and also showing connections to zona incerta, accessory optic system, pons, the contralateral vLGN/IGL, and other thalamic nuclei. Physiological studies indicate species differences, with spectral-sensitive responses common in some species, and varying populations of motion-sensitive units or units linked to optokinetic stimulation. A high percentage of IGL neurons show light intensity-coding responses. Behavioral studies suggest that the vLGN and IGL play a major role in mediating non-photic phase shifts of circadian rhythms, largely via neuropeptide Y, but may also play a role in photic phase shifts and in photoperiodic responses. The vLGN and IGL may participate in two major functional systems, those controlling visuomotor responses and those controlling circadian rhythms. Future research should be directed toward further integration of these diverse findings.     

Superior colliculus and active navigation: role of visual and non-visual cues in controlling cellular representations of space

To begin investigation of the contribution of the superior colliculus to unrestrained navigation, the nature of behavioral representation by individual neurons was identified as rats performed a spatial memory task. Similar to what has been observed for hippocampus, many superior collicular cells showed elevated firing as animals traversed particular locations on the maze, and also during directional movement. However, when compared to hippocampal place fields, superior collicular location fields were found to be more broad and did not exhibit mnemonic properties. Organism-centered spatial coding was illustrated by other neurons that discharged preferentially during right or left turns made by the animal on the maze, or after lateralized sensory presentation of somatosensory, visual, or auditory stimuli. Nonspatial movement-related neurons increased or decreased firing when animals engaged in specific behaviors on the maze regardless of location or direction of movement. Manipulations of the visual environment showed that many, but not all, spatial cells were dependent on visual information. The majority of movement-related cells, however, did not require visual information to establish or maintain the correlates. Several superior collicular cells fired in response to multiple maze behaviors; in some of these cases a dissociation of visual sensitivity to one component of the behavioral correlate, but not the other, could be achieved for a single cell. This suggests that multiple modalities influence the activity of single neurons in superior colliculus of behaving rats. Similarly, several sensory-related cells showed dramatic increases in firing rate during the presentation of multisensory stimuli compared to the unimodal stimuli. These data reveal for the first time how previous findings of sensory/motor representation by the superior colliculus of restrained/anesthetized animals might be manifested in freely behaving rats performing a navigational task. Furthermore, the findings of both visually dependent and visually independent spatial coding suggest that superior colliculus may be involved in sending visual information for establishing spatial representations in efferent structures and for directing spatially-guided movements.     

Intrinsic circuitry in the deep layers of the cat superior colliculus

The mammalian superior colliculus is involved in the transformation of sensory signals into orienting behaviors. Sensory and motor signals are integrated in the colliculus to produce movements of the eyes, head, and neck. While there is a considerable amount of information available on the afferent and efferent connections of the colliculus, almost nothing is known about its intrinsic circuitry, particularly that of its deepest layers. It is likely that intrinsic connections in these deeper layers of the colliculus participate in the sensory-motor transformations leading to orienting movements. In this study, we used the neuroanatomical tracer biocytin to label small groups of neurons in the deeper layers of the cat superior colliculus and examine the distribution of their axons and terminals. We found a broadly distributed network of intrinsic projections throughout the deep layers of the superior colliculus. While the majority of terminals were found in a 1-2 mm radius around the injection site, labeled terminals were found throughout the deep layers of the colliculus up to 5 mm from the injection site. In addition, these injections sometimes labeled terminals in the superficial tectum. Extensive projections were demonstrated by the more superficial injections, but few terminals were found when injections were confined to the deepest layers of the colliculus. There was no evidence of anisotropy in the distribution of terminals from injections made at different rostrocaudal or mediolateral locations; neurons located in any one region in the colliculus could potentially influence any other region. This network of intrinsic connections in the cat superior colliculus could provide a means for deeper-layer efferent neurons to associate, and to modulate or coordinate their output. Interneurons could also provide a substrate for mutual inhibition between neurons at the rostral pole of the colliculus that are active during fixation, and more caudally located neurons whose activity is associated with saccadic eye movements.     

Discharge properties of Purkinje cells in the oculomotor vermis during visually guided saccades in the macaque monkey

1. We previously described discharge properties of cerebellar output cells in the fastigial nucleus during ipsilateral and contralateral saccades. Fastigial cells exhibited unique responses depending on the direction of saccades and were involved in execution of accurate targeting saccades. Purkinje cells in the oculomotor vermis (lobules VIc and VII) are thought to modulate these discharges of fastigial cells. In this study we reexamine discharge properties of Purkinje cells on the basis of this hypothesis. 2. Initially we physiologically identified the right and left sides of the oculomotor vermis. Saccade-related discharges of 79 Purkinje cells were recorded from both sides of the vermis during visually guided saccades toward the sides ipsilateral and contralateral to the recording side in two trained macaque monkeys. To clarify the correlation of Purkinje cell discharge with burst activities in the fastigial nucleus during saccadic eye movements, we analyzed our data by employing methods used in the study of fastigial neurons. 3. Among the 79 cells, 56 (71%) showed burst discharges during saccades (saccadic burst cells). Of the 56 cells, 29 exhibited a peak of burst discharges in both the contralateral and ipsilateral directions (bidirectional cells). The remaining 27 saccadic burst cells showed a peak of burst discharges during either contralateral or ipsilateral saccades (unidirectional cells). Among the 79 cells, 14 (18%) exhibited a pause of discharges during contralateral saccades (pause cells). Among the 79 cells, 9 (11%) showed burst discharge during contralateral saccades followed by tonic discharge that was correlated with eye position (burst tonic cells). 4. The timing of bursts in bidirectional cells with respect to saccade onset was dependent on the direction of saccade. During ipsilateral saccades, Purkinje cells exhibited a long lead burst that built up gradually, peaked near the onset of the saccade, and terminated sharply near midsaccade. The mean lead time relative to saccade onset was 29.3 +/- 24.5 (SD) ms. During contralateral saccades, Purkinje cells exhibited a short lead/late burst that built up sharply, peaked near midsaccade, and terminated gradually after the end of the saccade. The mean lead time relative to saccade onset was 10.7 +/- 20.8 ms. The burst onset time during contralateral saccades and the burst offset time during ipsilateral saccades preceded the saccade offset time by about the same interval regardless of the saccade amplitude. 5. In pause cells the pause preceded saccade onset by 17.5 +/- 10.6 ms. The duration of the pause was not correlated with the duration of saccades. There was little trial-to-trial variability in the onset time of the pause with respect to the onset of saccades, whereas there was large trial-to-trial variability in the offset time of the pause with respect to the offset of saccades. In addition, the mean onset time of the pause for each cell had a relatively narrow distribution. 6. The burst lead time of burst tonic cells relative to saccade onset was 9.5 +/- 3.9 ms. The tonic discharge rate of burst tonic cells was a nonlinear function of eye position. The regression of each cell was fit to two lines. The regression coefficient ranged from 0.95 to 0.99 (mean = 0.97). 7. Axons of Purkinje cells in the oculomotor vermis are thought to project exclusively to saccadic burst cells in the fastigial oculomotor region (FOR), which is located in the caudal portion of the fastigial nucleus. Our previous studies indicated that FOR cells provide temporal signals for controlling targeting saccades. The present results suggest that Purkinje cells in the oculomotor vermis modify the temporal signals of FOR cells for saccades in different directions and amplitudes. The modification of FOR cell activity by Purkinje cells is thought to be essential for the function of the cerebellum in the control of saccadic eye movements.     

Neural network simulations of the primate oculomotor system. III. An one-dimensional, one-directional model of the superior colliculus

This report evaluates the performance of a biologically motivated neural network model of the primate superior colliculus (SC). Consistent with known anatomy and physiology, its major features include excitatory connections between its output elements, nigral gating mechanisms, and an eye displacement feedback of reticular origin to recalculate the metrics of saccades to memorized targets in retinotopic coordinates. Despite the fact that it makes no use of eye position or eye velocity information, the model can account for the accuracy of saccades in double step stimulation experiments. Further, the model accounts for the effects of focal SC lesions. Finally, it accounts for the properties of saccades evoked in response to the electrical stimulation of the SC. These include the approximate size constancy of evoked saccades despite increases of stimulus intensity, the fact that the size of evoked saccades depends on the time that has elapsed from a previous saccade, the fact that staircases of saccades are evoked in response to prolonged stimuli, and the fact that the size of saccades evoked in response to the simultaneous stimulation of two SC sites is the average of the saccades that are evoked when the two sites are separately stimulated.     

Effects of stimulus duration on responses of neurons in the chinchilla inferior colliculus

The effects of the stimulus duration (10 to 300 ms) on the responses of chinchilla inferior colliculus neurons to pure tones were studied in 41 units. The responses of the majority of the neurons (90%) were classified as sustained, onset, pause with onset peak and pause without onset peak response patterns. Three neurons were found to have response to the stimulus offset (offset response pattern). One neuron responded to the sound with the decrease of the spontaneous discharge rate (inhibitory response pattern). The responses restricted within the stimulus duration could be simply predicted from the peristimulus time histogram (PSTH) to the longer duration. The leading part of the PSTH to the longer stimulus duration resembled that to the shorter stimulus duration. The function of the spike number versus duration was correlated with the PSTH patterns. The response following the stimulus offset (including inhibitory response) could vary with the stimulus duration nonmonotonically and show a band-pass or band-reject property. Overall, four (about 10%) of the neurons could be regarded as duration-tuned units. The duration selectivity could be understood by the interaction between the ongoing and the offset process of the neurons.     

Dopamine efflux from the brain stem of the rat during feeding, drinking and lever-pressing for food

To determine whether endogenous dopamine (DA) is involved in the control of feeding and drinking, the cerebral activity of 14C-DA was examined in the rat while the animal consumed food or water. A push-pull guide tube was implanted above sites either adjacent to the third ventricle, the anterior hypothalamus or the substantia nigra in each of 41 rats. After the endogenous stores of DA at specific sites were labelled by a microinjection of 0.5 to 2.0 muCi of 14C-DA, an artificial CSF was perfused at half-hour intervals at a rate of 20-23 mul/min in these sites in the food deprived rat. After a 14C-washout curve of radioactivity in the perfusate was derived for successive control samples, the food-deprived rat was offered food or water which was ingested during the course of one or more perfusions. As the rat consumed food, 14C-DA was released in some experiments from circumscribed sites in the nucleus reuniens and the zona incerta. The efflux of 14C-DA from certain sites in the circumscribed sites in the nucleus reuniens and the zona incerta. The efflux of 14C-DA from certain sites in the ventromedial and dorsomedial hypothalamus as well as from the substantia nigra also was enhanced as the rat depressed a lever to obtain food pellets. Since 14C-DA was also released from the zona incerta, perifornical hypothalamus, and into the third ventricle as the rat drank water, these results suggest that dopaminergic neurons in the brain stem play some part in the motor component of ingestive behavior rather than feeding per se.     

Frontal eye field neurons orthodromically activated from the superior colliculus

Frontal eye field neurons orthodromically activated from the superior colliculus. J. Neurophysiol. 80: 3331-3333, 1998. Anatomical studies have shown that the frontal eye field (FEF) and superior colliculus (SC) of monkeys are reciprocally connected, and a physiological study described the signals sent from the FEF to the SC. Nothing is known, however, about the signals sent from the SC to the FEF. We physiologically identified and characterized FEF neurons that are likely to receive input from the SC. Fifty-two FEF neurons were found that were orthodromically activated by electrical stimulation of the intermediate or deeper layers of the SC. All the neurons that we tested (n = 34) discharged in response to visual stimulation. One-half also discharged when saccadic eye movements were made. This provides the first direct evidence that the ascending pathway from SC to FEF might carry visual- and saccade-related signals. Our findings support a hypothesis that the SC and the FEF interact bidirectionally during the events leading up to saccade generation.     

Locomotor stepping initiated by glutamate injections into the hypothalamus of the anesthetized rat.

Glutamate (50 mM, 50 nl) injected into the tuberal and posterior hypothalamus was tested for capacity to elicit locomotor stepping. Rats (n?=?23) were anesthetized with sodium pentobarbital and suspended by a sling in a stereotaxic apparatus such that locomotor stepping rotated a wheel. In 61 of 275 sites tested, stepping was initiated by glutamate injections within 60 sec. Positive sites were widespread and were contained in the lateral hypothalamus, the perifornical area, the dorsomedial nucleus, and the zona incerta. The perifornical and lateral hypothalamic sites were most likely to have locomotor responses and the shortest latencies. These findings indicate that selective activation of hypothalamic neurons as opposed to fibers of passage can initiate locomotion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Barley lipid-transfer protein complexed with palmitoyl CoA: the structure reveals a hydrophobic binding site that can expand to fit both large and small lipid-like ligands

The expression of cadherin-8 was mapped by in situ hybridization in the embryonic and postnatal mouse central nervous system (CNS). From embryonic day 18 (E18) to postnatal day 6 (P6), cadherin-8 expression is restricted to a subset of developing brain nuclei and cortical areas in all major subdivisions of the CNS. The anlagen of some of the cadherin-8-positive structures also express this molecule at earlier developmental stages (E12.5-E16). The cadherin-8-positive neuroanatomical structures are parts of several functional systems in the brain. In the limbic system, cadherin-8-positive regions are found in the septal region, habenular nuclei, amygdala, interpeduncular nucleus, raphe nuclei, and hippocampus. Cerebral cortex shows expression in several limbic areas at P6. In the basal ganglia and related nuclei, cadherin-8 is expressed by parts of the striatum, globus pallidus, substantia nigra, entopeduncular nucleus, subthalamic nucleus, zona incerta, and pedunculopontine nuclei. A third group of cadherin-8-positive gray matter structures has functional connections with the cerebellum (superior colliculus, anterior pretectal nucleus, red nucleus, nucleus of posterior commissure, inferior olive, pontine, pontine reticular, and vestibular nuclei). The cerebellum itself shows parasagittal stripes of cadherin-8 expression in the Purkinje cell layer. In the hindbrain, cadherin-8 is expressed by several cranial nerve nuclei. Results from this study show that cadherin-8 expression in the embryonic and postnatal mouse brain is restricted to specific developing gray matter structures. These data support the idea that cadherins are a family of molecules whose expression provides a molecular code for the regionalization of the developing vertebrate brain.