Kinetic analysis of open- and closed-state inactivation transitions in human Kv4.2 A-type potassium channels.

1. We studied the gating kinetics of Kv4.2 channels, the molecular substrate of neuronal somatodendritic A-type currents. For this purpose wild-type and mutant channels were transiently expressed in the human embryonic kidney (HEK) 293 cell line and currents were measured in the whole-cell patch-clamp configuration. 2. Kv4.2 channels inactivated from pre-open closed state(s) with a mean time constant of 959 ms at -50 mV. This closed-state inactivation was not affected by a deletion of the Kv4.2 N-terminus (Delta2-40). 3. Kv4.2 currents at +40 mV inactivated with triple-exponential kinetics. A fast component (tau = 11 ms) accounted for 73 %, an intermediate component (tau = 50 ms) for 23 % and a slow component (tau = 668 ms) for 4 % of the total decay. 4. Both the fast and the intermediate components of inactivation were slowed by a deletion of the Kv4.2 N-terminus (tau = 35 and 111 ms) and accounted for 33 and 56 %, respectively, of the total decay. The slow component was moderately accelerated by the truncation (tau = 346 ms) and accounted for 11 % of the total Kv4.2 current inactivation. 5. Recovery from open-state inactivation and recovery from closed-state inactivation occurred with similar kinetics in a strongly voltage-dependent manner. Neither recovery reaction was affected by the N-terminal truncation. 6. Kv4.2 Delta2-40 channels displayed slowed deactivation kinetics, suggesting that the N-terminal truncation leads to a stabilization of the open state. 7. Simulations with an allosteric model of inactivation, supported by the experimental data, suggested that, in response to membrane depolarization, Kv4.2 channels accumulate in the closed-inactivated state(s), from which they directly recover, bypassing the open state.

Conserved Kv4 N-terminal domain critical for effects of Kv channel-interacting protein 2.2 on channel expression and gating.

Association of Kv channel-interacting proteins (KChIPs) with Kv4 channels leads to modulation of these A-type potassium channels (An, W. F., Bowlby, M. R., Betty, M., Cao, J., Ling, H. P., Mendoza, G., Hinson, J. W., Mattsson, K. I., Strassle, B. W., Trimmer, J. S., and Rhodes, K. J. (2000) Nature 403, 553-556). We cloned a KChIP2 splice variant (KChIP2.2) from human ventricle. In comparison with KChIP2.1, coexpression of KChIP2.2 with human Kv4 channels in mammalian cells slowed the onset of Kv4 current inactivation (2-3-fold), accelerated the recovery from inactivation (5-7-fold), and shifted Kv4 steady-state inactivation curves by 8-29 mV to more positive potentials. The features of Kv4.2/KChIP2.2 currents closely resemble those of cardiac rapidly inactivating transient outward currents. KChIP2.2 stimulated the Kv4 current density in Chinese hamster ovary cells by approximately 55-fold. This correlated with a redistribution of immunoreactivity from perinuclear areas to the plasma membrane. Increased Kv4 cell-surface expression and current density were also obtained in the absence of KChIP2.2 when the highly conserved proximal Kv4 N terminus was deleted. The same domain is required for association of KChIP2.2 with Kv4 alpha-subunits. We propose that an efficient transport of Kv4 channels to the cell surface depends on KChIP binding to the Kv4 N-terminal domain. Our data suggest that the binding is necessary, but not sufficient, for the functional activity of KChIPs.

Coupling of voltage-dependent potassium channel inactivation and oxidoreductase active site of Kvbeta subunits.

The accessory beta subunits of voltage-dependent potassium (Kv) channels form tetramers arranged with 4-fold rotational symmetry like the membrane-integral and pore-forming alpha subunits (Gulbis, J. M., Mann, S., and MacKinnon, R. (1999) Cell. 90, 943-952). The crystal structure of the Kvbeta2 subunit shows that Kvbeta subunits are oxidoreductase enzymes containing an active site composed of conserved catalytic residues, a nicotinamide (NADPH)-cofactor, and a substrate binding site. Also, Kvbeta subunits with an N-terminal inactivating domain like Kvbeta1.1 (Rettig, J., Heinemann, S. H., Wunder, F., Lorra, C., Parcej, D. N., Dolly, O., and Pongs, O. (1994) Nature 369, 289-294) and Kvbeta3.1 (Heinemann, S. H., Rettig, J., Graack, H. R., and Pongs, O. (1996) J. Physiol. (Lond.) 493, 625-633) confer rapid N-type inactivation to otherwise non-inactivating channels. Here we show by a combination of structural modeling and electrophysiological characterization of structure-based mutations that changes in Kvbeta oxidoreductase activity may markedly influence the gating mode of Kv channels. Amino acid substitutions of the putative catalytic residues in the Kvbeta1.1 oxidoreductase active site attenuate the inactivating activity of Kvbeta1.1 in Xenopus oocytes. Conversely, mutating the substrate binding domain and/or the cofactor binding domain rescues the failure of Kvbeta3.1 to confer rapid inactivation to Kv1.5 channels in Xenopus oocytes. We propose that Kvbeta oxidoreductase activity couples Kv channel inactivation to cellular redox regulation.

Repetitive firing deficits and reduced sodium current density in retinal ganglion cells developing in the absence of BDNF.

Previous work by Cellerino et al. has shown that chronic absence of brain-derived neurotrophic factor (BDNF) resulted in hypomyelination of the optic nerve. Since myelination is influenced by neuronal activity, it is possible that a deficiency in BDNF during early development could alter the firing properties of retinal neurons. To test this hypothesis, patch-clamp recordings were performed in retinal whole mounts from BDNF-deficient (bdnf-/-), heterozygote (bdnf+/-) or wild-type control mice (bdnf+/+). Ganglion cell layer neurons (RGNs) were tested at different age [postnatal day (P)1-11] for their ability to encode graded depolarization with variable action potential frequency. At all developmental ages examined, RGNs exhibiting frequency coding were less frequently encountered in bdnf-/- than in bdnf+/+ mice. At P1, none of the RGNs from bdnf-/- mice displayed repetitive firing compared to 50% in bdnf+/+ mice, and by P7-11, only 50% of bdnf-/- RGNs exhibited repetitive firing compared to 100% in bdnf+/+ mice. Moreover, in bdnf-/- RGNs repetitive discharge was characterized by a reduced frequency increment per current change. Acquisition of repetitive firing was paralleled by a decrease in input resistance and a steep increase of sodium current density. In bdnf-/- mice, the onset of this increase occurred at later stages of development than in wild-type controls (bdnf-/-: P6-11; bdnf+/+: P2-6). The discharge pattern of P7-11 bdnf-/- RGNs resembled that of RGNs in neonatal wild-type mice and was mimicked by acute application of a Ca(2+) channel blocker. We conclude that BDNF plays an important role in the ontogeny of repetitive firing of RGNs.

Functional and molecular aspects of voltage-gated K+ channel beta subunits.

Voltage-gated potassium channels (Kv) of the Shaker-related superfamily are assembled from membrane-integrated alpha subunits and auxiliary beta subunits. The beta subunits may increase Kv channel surface expression and/or confer A-type behavior to noninactivating Kv channels in heterologous expression systems. The interaction of Kv alpha and Kv beta subunits depends on the presence or absence of several domains including the amino-terminal N-type inactivating and NIP domains and the Kv alpha and Kv beta binding domains. Loss of function of Kv beta 1.1 subunits leads to a reduction of A-type Kv channel activity in hippocampal and striatal neurons of knock-out mice. This reduction may be correlated with altered cognition and motor control in the knock-out mice.

Ion conductances related to development of repetitive firing in mouse retinal ganglion neurons in situ.

In the retina, the ability to encode graded depolarizations into spike trains of variable frequency appears to be a specific property of retinal ganglion neurons (RGNs). To deduce the developmental changes in ion conductances underlying the transition from single to repetitive firing, patch-clamp recordings were performed in the isolated mouse retina between embryonic day 15 (E15) and postnatal day 5 (P5). Immature neurons of the E15 retina were selected according to their capacity to generate voltage-activated Na+ currents (I(Na)(v)). Identification of P5 RGNs was based on retrograde labeling, visualization of the axon, or the amplitude of I(Na)(v). At E15, half of the cells were excitable but none of them generated more than one spike. At P5, all cells were excitable and a majority discharged in tonic fashion. Ion conductances subserving maintenance of repetitive discharge were identified at P5 by exposure to low extracellular Ca2+, Cd2+, and charybdotoxin, all of which suppressed repetitive discharge. omega-Conotoxin GVIA and nifedipine had no effect. We compared passive membrane properties and a variety of voltage-activated ion channels at E15 and P5. It was found that the density of high voltage-activated (HVA) Ca2+ currents increased in parallel with the development of repetitive firing, while the density of Ni2+-sensitive low voltage-activated (LVA) Ca2+ currents decreased. Changes in density and activation kinetics of tetrodotoxin-sensitive Na+ currents paralleled changes in firing thresholds and size of action potentials, but seemed to be unrelated to maintenance of repetitive firing. Densities of A-type K+ currents and delayed rectifier currents did not change. The results suggest that HVA Ca2+ channels, and among them a toxin-resistant subtype, are specifically engaged in activation of Ca2+-sensitive K+ conductance and thereby account for frequency coding in postnatal RGNs.

The role of hydrophobic interactions in binding of polyamines to non NMDA receptor ion channels.

Block of kainate subtype glutamate receptor channels by internal polyamines was analysed using outside out patches from HEK 293 cells transiently transfected with GluR6(Q). Tetramines with different numbers and spacing of methylene groups between NH2 groups produced biphasic rectification well fit by the Woodhull model for a weakly permeable ion channel blocker. Such analysis revealed an increase in binding energy of 611 cal M(-1) for each methylene group added over the range 6-12 (CH2), suggesting that a major component of block by polyamines involves hydrophobic binding. Isomers with the same number of CH2 groups but different spacing between NH2 groups showed similar affinity. Due to differences in pKa values for protonation of NH2 groups, the average charge on the tetramines studied would be expected to vary from 3.98 to 2.22 at physiological pH; despite this, the voltage dependence of block was similar for all tetramines tested, with a mean value for ztheta of 1.82, similar to values for polyamines with five or six NH2 groups. In contrast, for 1,3-propane diamine (DA3 ztheta 0.83), and the N-propyl- (ztheta 1.42) and N,N'-diethyl- (ztheta 1.37) analogues of DA3, there was an increase in the voltage dependence of block on addition of hydrophobic groups.

Coexpression of the KCNA3B gene product with Kv1.5 leads to a novel A-type potassium channel.

Shaker-related voltage-gated potassium (Kv) channels may be heterooligomers consisting of membrane-integral alpha-subunits associated with auxiliary cytoplasmic beta-subunits. In this study we have cloned the human Kvbeta3.1 subunit and the corresponding KCNA3B gene. Identification of sequence-tagged sites in the gene mapped KCNA3B to band p13.1 of human chromosome 17. Comparison of the KCNA1B, KCNA2B, and KCNA3B gene structures showed that the three Kvbeta genes have very disparate lengths varying from >/=350 kb (KCNA1B) to approximately 7 kb (KCNA3B). Yet, the exon patterns of the three genes, which code for the seven known mammalian Kvbeta subunits, are very similar. The Kvbeta1 and Kvbeta2 splice variants are generated by alternative use of 5'-exons. Mouse Kvbeta4, a potential splice variant of Kvbeta3, is a read-through product where the open reading frame starts within the sequence intervening between Kvbeta3 exons 7 and 8. The human KCNA3B sequence does not contain a mouse Kvbeta4-like open reading frame. Human Kvbeta3 mRNA is specifically expressed in the brain, where it is predominantly detected in the cerebellum. The heterologous coexpression of human Kv1.5 and Kvbeta3.1 subunits in Chinese hamster ovary cells yielded a novel Kv channel mediating very fast inactivating (A-type) outward currents upon depolarization. Thus, the expression of Kvbeta3.1 subunits potentially extends the possibilities to express diverse A-type Kv channels in the human brain.

An analysis of philanthotoxin block for recombinant rat GluR6(Q) glutamate receptor channels.

1. The action of philanthotoxin 343 (PhTX) on rat homomeric GluR6(Q) recombinant glutamate receptor channels was analysed using concentration-jump techniques and outside-out patches from HEK 293 cells. Both onset and recovery from block by external PhTX were dependent on the presence of agonist, indicating that channels must open for PhTX to bind and that channel closure can trap PhTX. 2. Block by external PhTX developed with double-exponential kinetics. The rate of onset of the fast component of block showed an exponential increase per 27 mV hyperpolarization over the range -40 to -100 mV. The rate of onset of the slow component of block showed a non-linear concentration dependence indicating a rate-limiting step in the blocking mechanism. 3. The extent of block by 1 microM external PhTX was maximal at -40 mV and did not increase with further hyperpolarization; the rate of recovery from block by external PhTX increased 6-fold on hyperpolarization from -40 to -100 mV suggesting that PhTX permeates at negative membrane potentials. 4. Apparent Kd values for block by external PhTX estimated from dose-inhibition experiments decreased 300-fold on hyperpolarization from +40 mV (Kd, 19.6 microM) to -40 mV (Kd, 69 nM); there was little further increase in affinity with hyperpolarization to -80 mV (Kd, 56 nM), consistent with permeation of PhTX at negative membrane potentials. 5. Block by internal PhTX showed complex kinetics and voltage dependence. Analysis with voltage ramps from -120 to +120 mV indicated a Kd at 0 mV of 20 microM, decreasing e-fold per 16 mV depolarization. However, at +90 mV the extent of block by 1 and 10 microM internal PhTX (73 % and 95 %, respectively) reached a maximum and did not increase with further depolarization. 6. Voltage-jump analysis of block by 100 microM internal PhTX revealed partial trapping. With 100 ms jumps from -100 to -40 mV, onset and recovery from block were complete within 5 ms. With jumps of longer duration the extent of block increased, with a time constant of 8.1 s, reaching 84 % at 30 s. On repolarization to -100 mV, recovery from block showed fast and slow components. 7. The amplitude of the slow component of block by internal PhTX showed a biphasic voltage dependence, first increasing then decreasing with progressive depolarization. Maximum block was obtained at 0 mV. 8. Our results suggest that PhTX acts as an open channel blocker; however, provided that the toxin remains bound to the channel, an allosteric mechanism destabilizes the open state, inducing channel closing and trapping PhTX. Strong depolarization for internal PhTX, or strong hyperpolarization for external PhTX, forces the toxin to permeate before it triggers entry into closed blocked states.

Evaluation of temperature increase with different amounts of magnetite in liver tissue samples.

RATIONALE AND OBJECTIVES: The biologic effects of magnetically induced heating effects using iron oxide, magnetite, were examined in vitro in liver tissue samples as a first step toward potential applications in cancer therapy. METHODS: For the determination of the temperature profile around an iron oxide sample, a cylinder containing 170 mg of magnetite was constructed and placed into pureed liver tissue from pig, together with thermocouples of copper and constantan wires positioned at defined distances from it. Temperature measurements were performed during the exposure to an alternating magnetic field (frequency: 400 kHz; amplitude: approximately 6.5 kA/m) generated by a circular coil (90 mm of diameter). Moreover, variable amounts of magnetite (dissolved in approximately 0.2 mL physiologic saline) were injected directly into carrageenan gels. During the exposure to a magnetic field for 4 minutes the temperature increase was determined in the area of iron oxide deposition using a thermocouple. Additionally, variable amounts of magnetite were injected directly into isolated liver tissue samples (diameter: 20 mm; height: 30 mm) and exposed to a magnetic field for 2 minutes. The extent of the induced macroscopically visible tissue alterations (light brown colorations caused by heating) was examined by means of volume estimations. The degrees of cellular necrosis were investigated by histopathologic studies. RESULTS: The temperature profile around a magnetite cylinder revealed a significant decrease of temperature difference between the beginning and the end of heating, depending on increasing distance from the sample center. The extent of the temperature difference correlated with increasing heating time. No significant variations of temperature were observed at a distance of approximately 12 mm from the sample center. A good correlation (r = 0.98) between the injected amounts (31 to 200 mg) and the temperature increase since the start of heating (6.8-33.7 degrees C) in the area of iron oxide deposits was detected. The volume of damaged liver tissue was approximately seven times higher than the injected volume of iron oxide dispersion. Histologically different degrees of cellular necrosis were observed. CONCLUSIONS: The parameters determined in this article show that iron oxides are able to induce considerable heating effects in the surroundings. After an adequate optimization of the technical procedure, it is conceivable that heating properties of magnetites can be used in future cancer treatments.

Permeation and block of rat GluR6 glutamate receptor channels by internal and external polyamines.

1. Polyamine block of rat GluR6(Q) glutamate receptor channels was studied in outside-out patches from transiently transfected HEK 293 cells. With symmetrical 150 mM Na+ and 30 microM internal spermine there was biphasic voltage dependence with 95% block at +40 mV but only 20% block at +140 mV. Dose-inhibition analysis for external spermine also revealed biphasic block; the Kd at +40 mV (54 microM) was lower than at +80 (167 microM) and -80 mV (78 microM). 2. For internal polyamines relief from block was most pronounced for spermine, weaker for N-(4-hydroxyphenylpropanoyl)-spermine (PPS), and virtually absent for philanthotoxin 343 (PhTX 343), suggesting that permeation of polyamines varies with cross-sectional width (spermine, 0.44 nm; PPS, 0.70 nm; PhTX 343, 0.75 nm). 3. With putrescine, spermidine, or spermine as sole external cations, inward currents at -120 mV confirmed permeation of polyamines. For bi-ionic conditions with 90 mM polyamine and 150 mM Na+i, reversal potentials were -12.4 mV for putrescine (permeability ratio relative to Na+, PPut/PNa = 0.42) and -32.7 mV for spermidine (PSpd/PNa = 0.07). Currents carried by spermine were too small to analyse accurately in the majority of patches. 4. Increasing [Na+]i from 44 to 330 mM had no effect on the potential for 50% block (V1/2) by 30 microM internal spermine; however, relief from block at positive membrane potentials increased with [Na+]i. In contrast, raising [Na+]o from 44 to 330 mM resulted in a depolarizing shift in V1/2, indicating a strong interaction between internal polyamines and external permeant ions. 5. The Woodhull infinite barrier model of ion channel block adequately described the action of spermine at membrane potentials insufficient to produce relief from block. For 30 microM internal spermine such analysis gave Kd(O) = 2.5 microM, z theta = 1.97; block by 30 microM external spermine was weaker and less voltage dependent (Kd(O) = 37.8 microM and z delta = 0.55); delta and theta are electrical distances measured from the outside and inside, respectively. 6. Fits of the Woodhull equation for a permeable blocker adequately described both onset and relief from block by spermine over a wide range of membrane potentials. However, the rate constants and z delta values estimated for block by internal spermine predicted much stronger external block than was measured experimentally, and vice versa. 7. An Eyring rate theory model with two energy wells and three barriers explained qualitatively many characteristic features of the action of polyamines on GluRs, including biphasic I-V relationships, weaker block by external than internal spermine and low permeability.

AMPA receptor heterogeneity in rat hippocampal neurons revealed by differential sensitivity to cyclothiazide.

1. The kinetics of onset of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor desensitization by glutamate, and the extent of attenuation of AMPA receptor desensitization by cyclothiazide, showed pronounced cell-to-cell variation in cultures of rat hippocampal neurons. Cultures prepared from area CA1 stratum radiatum tended to show weaker modulation by cyclothiazide than cultures prepared from the whole hippocampus. 2. Kinetic analysis of concentration jump responses to glutamate revealed multiple populations of receptors with fast (approximately 400 ms), intermediate (approximately 2-4 s), and slow (> 20 s) time constants for recovery from modulation by cyclothiazide. The amplitudes of these components varied widely between cells, suggesting the existence of at least three populations of AMPA receptor subtypes, the relative density of which varied from cell to cell. 3. The complex patterns of sensitivity to cyclothiazide seen in hippocampal neurons could be reconstituted by assembly of recombinant AMPA receptor subunits generated from cDNAs encoding the flip (i) and flop (o) splice variants of the GluR-A and GluR-B subunits. Recovery from modulation by cyclothiazide was slower for GluR-AiBi and GluR-AoBi than for GluR-AiBo and GluR-AoBo. 4. Coexpression of the flip and flop splice variants of GluR-A, in the absence of GluR-B, revealed that heteromeric AMPA receptors with intermediate sensitivity to cyclothiazide, similar to responses observed for the combinations GluR-AoBi or GluR-AiBo, could be generated independently of the presence of the GluR-B subunit. However, recovery from modulation by cyclothiazide was twofold slower for GluR-AiBi than for homomeric GluR-Ai, indicating that the GluR-A and GluR-B subunits are not functionally equivalent in controlling sensitivity to cyclothiazide. 5. These results demonstrate that AMPA receptors expressed in hippocampal neurons are assembled in a variety of subunit and splice variant combinations that might serve as a mechanism to fine-tune the kinetics of synaptic transmission.

Differential modulation by sulfhydryl redox agents and glutathione of GABA- and glycine-evoked currents in rat retinal ganglion cells.

Some areas of the mammalian CNS, such as the retina, contain not one but two fast inhibitory neurotransmitter systems whose actions are mediated by GABA and glycine. Each inhibitory receptor system is encoded by a separate gene family and has a unique set of agonists and antagonists. Therefore, in rat retinal ganglion cells we were surprised to find that a single agent, extracellular glutathione, was capable of modulating currents activated by either GABAA or glycine receptor stimulation. Both oxidized and reduced glutathione influence inhibitory neurotransmission in a manner similar to that of the sulfhydryl redox agents dithiothreitol (DTT) and 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB). Remarkably, the actions of glutathione are diametrically opposed on the GABAA and glycine systems. In whole-cell recordings of single retinal ganglion cells with patch pipettes, reduced glutathione enhances GABA-evoked currents but decreases glycine-evoked currents. These findings suggest that endogenous redox agents, such as glutathione, may constitute a novel modulatory system for the differential regulation of inhibitory neurotransmission in the mammalian retina.

GABA-activated chloride currents of postnatal mouse retinal ganglion cells are blocked by acetylcholine and acetylcarnitine: how specific are ion channels in immature neurons?

The goal of this study was to clarify pharmacological properties of GABAA receptors in cells of the mouse retinal ganglion cell layer in situ. Spontaneous synaptic currents and responses to exogenous GABA were recorded from individual neurons in retinal whole mounts (postnatal days 1-3) or retinal stripe preparations (postnatal days 4-6). Drugs were applied by a fast local superfusion system. Current responses were measured with the patch-clamp technique in the whole-cell configuration. All cells responded to exogenous GABA (average EC50 and Hill coefficient: 16.7 microM and 0.95 respectively) and generated GABAergic synaptic currents in response to elevated KCl. GABA-induced currents of retinal ganglion cells were blocked by bicuculline, picrotoxin and Zn2+, as well as strychnine, and increased by pentobarbital, clonazepam and 3 alpha-hydroxy-5 alpha-pregnan-20-one. In some retinal ganglion cells GABA caused an increase in the frequency of spontaneous synaptic currents, which points to a partially depolarizing action of this traditionally inhibitory neurotransmitter in the neural retina. Our major observation is that acetylcholine and acetylcarnitine blocked or reduced GABAergic inhibitory postsynaptic currents and responses to exogenous GABA. This effect was seen in only a fraction of retinal ganglion cells and occurred in both the undesensitized and the desensitized state of the GABAA receptor. The block was voltage-independent and persisted during coapplication with the nicotinic and muscarinic acetylcholine receptor antagonists D-tubocurarine and atropine. In contrast to GABA-activated Cl- currents, glycine-activated Cl- currents remained unaffected by acetylcholine and acetylcarnitine.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral ablation of the frontal eye field of the rat affects the beating field of ocular nystagmus.

Spontaneous saccadic orientation and compensatory eye movements in response to optokinetic and vestibular velocity steps were studied in head-restrained, pigmented rats before and 1-2 weeks after unilateral ablation of the frontal eye field (FEF). One group of rats (n = 5) received a deep lesion and another group of rats (n = 4) received a superficial lesion of the left FEF. Postoperative response parameters such as the duration of slow buildup of eye velocity, the steady state velocity gain, the duration of optokinetic afternystagmus and of per- and postrotatory vestibular nystagmus were similar in the two groups of rats and did not differ from preoperative values measured in the same individuals. Superimposed upon these velocity components of nystagmus was a transient orienting response that expressed itself by a shift of the beating field of nystagmus in quick phase direction (gaze shift). The amplitudes of this gaze shift in quick phase direction were asymmetric in rats with a deep FEF lesion. Gaze shift amplitudes toward the side of the lesion were significantly enhanced and gaze shift amplitudes toward the intact side were significantly reduced. Similar asymmetries were observed in the distribution of spontaneous orienting movements of these rats in the light. Spontaneous saccadic eye movements of the same animals in darkness, however, were symmetric in amplitude to either side. These deficits suggest a partial sensory hemineglect after a deep unilateral lesion of the FEF and an involvement of this structure in the selective attention for targets in visual space. Thus the FEF orients the gaze at rest by means of saccades toward points of interest and during simulated circular locomotion by means of a shift of the beating field of nystagmus toward the visual sector that will be approached next.