The postnatal development of thalamocortical projections from the pulvinar in the cat

Summary The postnatal development of thalamocortical projections from the pulvinar to an association cortex of the cat, the crown of the middle suprasylvian gyrus, was studied by using both HRP and evoked field potentials. From birth onward, the pulvinar sends dense fibres to this cortical area, but the cortical laminar distribution of the afferents was found to change markedly with aging. An orthograde HRP study showed that at birth and up to 2 weeks of age, the terminals are distributed mainly in layer I, whereas in adult cats and kittens older than 1 month, the terminals are found largely in and around layer IV and only sparsely in layer I. After HRP injections exclusively into layer I of the crown, numerous thalamic neurones were retrogradely labelled in both the ventroanterior-ventrolateral complex (VA-VL) and the pulvinar in 5-day-old kittens, but in the VAVL alone in 2-month-old kittens. In agreement with these anatomical findings, stimulation of the pulvinar elicited a surface-negative, depth-positive potential in 1-week-old kittens, indicating the existence of a large current sink in layer I; however, it induced a surface-positive, depth-negative potential in 1month-old kittens, reflecting the presence of a strong current sink in the deep cortical layers.     

Response properties of neurons in the visual cortex of the rat

Summary Response properties of neurons in the visual cortex, area 17, of Long Evans pigmented rats were investigated quantitatively with computer-controlled stimuli. Ninety percent of the cells recorded (296/327) were responsive to visual stimulation. The majority (95%, 281/296) responded to moving images and were classified as complex (44%), simple (27%), hypercomplex (13%) and non-oriented (16%) according to criteria previously established for cortical cells in the cat and monkey. The remaining 5% of the neurons responded only to stationary stimuli flashed on-off in their receptive field. Results of this study indicate that neurons of the rat visual cortex have properties similar to those of cells in the striate cortex of more visual mammals.Supported by grant EY02964, the Biological Humanics Foundation and the Bendix Corporation     

Reversible inactivation of macaque frontal eye field

 The macaque frontal eye field (FEF) is involved in the generation of saccadic eye movements and fixations. To better understand the role of the FEF, we reversibly inactivated a portion of it while a monkey made saccades and fixations in response to visual stimuli. Lidocaine was infused into a FEF and neural inactivation was monitored with a nearby microelectrode. We used two saccadic tasks. In the delay task, a target was presented and then extinguished, but the monkey was not allowed to make a saccade to its location until a cue to move was given. In the step task, the monkey was allowed to look at a target as soon as it appeared. During FEF inactivation, monkeys were severely impaired at making saccades to locations of extinguished contralateral targets in the delay task. They were similarly impaired at making saccades to locations of contralateral targets in the step task if the target was flashed for ≤100 ms, such that it was gone before the saccade was initiated. Deficits included increases in saccadic latency, increases in saccadic error, and increases in the frequency of trials in which a saccade was not made. We varied the initial fixation location and found that the impairment specifically affected contraversive saccades rather than affecting all saccades made into head-centered contralateral space. Monkeys were impaired only slightly at making saccades to contralateral targets in the step task if the target duration was 1000 ms, such that the target was present during the saccade: latency increased, but increases in saccadic error were mild and increases in the frequency of trials in which a saccade was not made were insignificant. During FEF inactivation there usually was a direct correlation between the latency and the error of saccades made in response to contralateral targets. In the delay task, FEF inactivation increased the frequency of making premature saccades to ipsilateral targets. FEF inactivation had inconsistent and mild effects on saccadic peak velocity. FEF inactivation caused impairments in the ability to fixate lights steadily in contralateral space. FEF inactivation always caused an ipsiversive deviation of the eyes in darkness. In summary, our results suggest that the FEF plays major roles in (1) generating contraversive saccades to locations of extinguished or flashed targets, (2) maintaining contralateral fixations, and (3) suppressing inappropriate ipsiversive saccades. Received: 2 February 1996 / Accepted: 26 February 1997     

磁场对微循环的影响

为了探讨磁场对微循环的作用，利用直径０．７ｃｍ、表面磁感强度０．３Ｔ的磁片及磁感强度０．１Ｔ、转速２５００ｒ／ｍｉｎ的旋磁机分别作用于受试者左手无名指３０ｍｉｎ，并记录作用前后微循环改变。结果表明，动、静磁场均可使微血管清晰度、血流速及管径有明显改变，而对管袢数与红细胞聚集没有影响。这一结果提示，微血管扩张、血流速加快是磁场改善微循环的基础。     

Adrenaline and the plateau phase of the cardiac action potential

Summary Conduction block in heart cells by K⁺ rich, or Na⁺ depleted solutions can be overcome by adrenaline. In order to explain this phenomenon, the effect of adrenaline on the membrane resting and action potentials of cow Purkinje fibers was measured at various extracellular concentrations of Na⁺, K⁺ and Ca⁺⁺, in the presence of tetrodotoxin, Mn⁺⁺ and beta-receptor antagonists.It was found that adrenaline specifically increases the amplitude and duration of the plateau phase of the cardiac action potential. Plateu-like action potentials, without preceding Na⁺-spike, can be generated and conducted in an all-or-nothing way. In K⁺ rich solutions and under the influence of adrenaline, the depolarization proceeds in two steps. The first step corresponds to the Na⁺-spike. The second step or secondary depolarization corresponds to the plateau; it was not modified by changes of the membrane potential between –85 and –55 mV, or by reduction of extracellular Na⁺ ions, but was specifically blocked by Mn⁺⁺ ions and beta-receptor antagonists. Its amplitude increased by 17 mV for a tenfold change in extracellular Ca⁺⁺. Tetrodotoxin preferentially blocked the Na⁺-spike, but also slowed the rate of potential change during the secondary depolarization.The simplest explanation for the observed phenomena can be found in an increase of Ca⁺⁺ inward current under the influence of adrenaline. The existence of an inward Na⁺⁺ current, different in characteristics from the Na⁺ conductance during the fast upstroke, cannot be ruled out. Some data are in accord with a decrease in K⁺ conductance.     

Removal of GABAergic inhibition alters subthreshold input in neurons in forepaw barrel subfield (FBS) in rat first somatosensory cortex (SI) after digit stimulation

Our objective was to test the hypothesis that suppression of GABAergic inhibition results in an enhancement of responses to stimulation of the surround receptive field. Neurons in the forepaw barrel subfield (FBS) in rat first somatosensory cortex (SI) receive short latency suprathreshold input from a principal location on the forepaw and longer latency subthreshold input from surrounding forepaw skin regions. Input from principal and surround receptive field sites was examined before, during, and after administration of the GABA(A) receptor blocker bicuculline methiodide (BMI) (in 165 mM NaCl at pH 3.3-3.5). In vivo extracellular recording was used to first identify the location of the glabrous forepaw digit representation within the FBS. In vivo intracellular recording and labeling techniques were then used to impale single FBS neurons in layer IV as well as neurons in layers III and V, determine the receptive field of the cell, and fill the cell with biocytin for subsequent morphological identification. The intracellular recording electrode was fastened with dental wax to a double-barrel pipette for BMI iontophoresis and current balance. A stimulating probe, placed on the glabrous forepaw skin surface, was used to identify principal and surround components of the receptive field. Once a cell was impaled and a stable recording was obtained, a stimulating probe was placed at a selected site within the surround receptive field. Single-pulse stimulation (1 Hz) was then delivered through the skin probe and the percentage of spikes occurring in 1-min intervals before BMI onset was used as a baseline measure. BMI was then iontophoresed while the periphery was simultaneously stimulated, and spike percentage measured during and after BMI ejection was compared with the pre-BMI baseline. The major findings are: (1) suppression of GABAergic inhibition enhanced evoked responses to firing level from sites in surround receptive fields in 65% of the cells ( n=17); (2) evoked responses were rapidly elevated (within 1 min) to suprathreshold firing in the presence of BMI in 31% of the cells; (3) GABAergic inhibition was reversible [suprathreshold spiking gradually reversed to subthreshold excitatory postsynaptic potentials (EPSPs) in 45% of the cells tested]; (4) BMI altered the stimulus-evoked and non-stimulus-evoked firing pattern in SI neurons from single spikes to burst patterns in all tested cells; and (5) iontophoresis of NaCl (165 mM) without BMI was ineffective in altering evoked responses in control cells ( n=4). The present findings support the notion that subthreshold input from surround receptive fields is one possible mechanism for rapid cortical reorganization in barrel cortex and that GABAergic inhibition may regulate its expression. Possible corticocortical and thalamocortical substrates for subthreshold input to reach barrel neurons are discussed.     

Compensation of labyrinthine lesions: effects of trigeminal neurotomy on vestibular field potentials

The aim of the research was to analyse the vestibular nuclear activity before and after the section of the 5th cranial nerve in chronically hemilabyrinthectomized guinea pigs during the stage of compensation. The animals were hemilabyrinthectomized (chloroform and vaselin oil into the right middle ear) and upon compensation (24–45 days), field potentials were recorded from the vestibular nuclei of the intact side following electrical stimulation of the ipsilateral labyrinthine receptors. Then the left trigeminal trunk was sectioned ventrally through the foramen lacerum and ovale which are fused in the guinea pig and the vestibular field potentials were again recorded for a period of 120 min. Trigeminal neurotomy modified the vestibular field potentials determining an increment in amplitude of 30–50% of N₁ and N₂ waves, configuration and latency remained unaltered. The dependence of vestibular compensation on trigeminal afferents is discussed on the light of reported results.     

Interhemispheric influences on area 19 of the cat

Summary Anatomical studies have shown an extensive network of homotopic and heterotopic interhemispheric connections in area 19 of the cat visual cortex (Segraves and Rosenquist 1982a; 1982b). We have investigated their functional organization by recording visual responses in area 19 of cats following a midsagittal section of the optic chiasm. This operation interrupts all crossed optic fibers coming both from the nasal and the temporal retinae; as a result, each hemisphere receives optic fibers only from the lateral hemiretina of the ipsilateral eye which conveys information from the contralateral visual field. Visual information transmitted to the same hemisphere from the contralateral retina and the ipsilateral visual field must be attributed to an indirect, interhemispheric pathway. We found that a rather high proportion of neurons (31.8%) in area 19 of seven split-chiasm cats responded to visual stimuli presented to the contralateral eye. 1 — All neurons receiving this interhemispheric activation were also driven by the ipsilateral eye via an intrahemispheric pathway. 2 — The property of binocularity was significantly related to the visuotopic map in that both receptive fields of each binocular neuron adjoined or were in the immediate vicinity of the vertical meridian. 3 — Due to the small size of receptive fields in area 19, the contribution of the interhemispheric pathway to the representation of the visual field is rather limited and it is certainly less extensive than that predicted by anatomical studies. The representation of the ipsilateral visual field in area 19 of intact cats, as assessed electrophy-siologically, was comparable to that found in split-chiasm cats. Recordings in areas 17–18 of split-chiasm cats showed that the visual field represented through the corpus callosum in these visual areas is certainly not less and probably more, extensive than that found in area 19. The results support the conclusion that the relation to the vertical meridian and the receptive field size can explain the organization of the interhemispheric connections in the visual areas studied so far.     

Bilateral receptive field neurons in the hindlimb region of the postcentral somatosensory cortex in awake macaque monkeys

Single-neuron activities were recorded in the hindlimb region of the primary somatosensory cortex and part of area 5 in awake Japanese monkeys. A total of 1050 units were isolated from five hemispheres of four animals. Receptive fields (RFs) and submodalities were identified for 90% of isolated neurons in areas 3a and 3b. The percentage decreased as the recoding site moved to the more caudal areas. Deep or skin submodality neurons were dominant in area 3a or area 3b, respectively. Deep submodality neurons increased in more caudal areas and were the majority in areas 2 and 5. These observations were consistent with those in the hand and/or digit or arm and/or trunk region. The identified neurons were classified by their RF positions into four types: the foot, leg, foot and leg, or hindlimb and other body parts type. Among 831 identified neurons, 33 neurons had bilateral RFs, 14 had ipsilateral RFs, and the rest (N=784) had contralateral RFs. The relative incidence of neurons with bilateral or ipsilateral RFs among identified neurons was less than 1% in areas 3a, 3b, and 1, and 16% or 25% in areas 2 or 5, respectively. Within areas 2 and 5, the percentage of neurons with bilateral or ipsilateral RFs was significantly smaller in the foot type (5%) than in other RF types (24-57%). RFs of the foot type were on the sole or single toe but never on multiple toes. These observations contrasted with the previous findings that neurons with bilateral RFs were more frequently seen in the hand and/or digit region and that RFs on multiple digit tips were dominant there. The present study thus demonstrated that neurons with bilateral RFs do exist in the hindlimb region. Similarly to the forelimb region, they were found mostly in areas 2 and 5, the caudalmost areas of the postcentral gyrus and hierarchically higher stages in information processing. The relative paucity of neurons with bilateral RFs on the foot, especially those with RFs on multiple toes, may reflect functional differences between the foot and the hand.     

Double-opponent-process mechanism underlying RF-structure of directionally specific cells of cat lateral suprasylvian visual area

Summary For the experiments reported in this study, recordings were obtained from 246 single units in the middle lateral suprasylvian visual area (LS) of 13 cats. 49 of these cells were subjected to detailed quantitative analysis. The receptive field (RF) organization was examined for directionally specific cells by presenting moving single spots on large moving random dot backgrounds. A cell's response to an optimal spot (in terms of size, direction, velocity) moving on a stationary background inside the excitatory RF (ERF) was compared to in-phase (same direction, same velocity) and anti-phase (opposite direction, same velocity) movement of spot and background. In-phase movement resulted in inhibition of the cell's response (3–100%) in 94% of the cells, while anti-phase movement led to reduced inhibition in 52% of the cells or to facilitation (0.5–327%) in 39% of the cells. By changing the direction of background motion with respect to that of the spot, the directional tuning of the in-phase inhibition and anti-phase facilitation effects was determined.We were able to manipulate the size of the background effects by masking out the background for various proportions of the ERF, and maximizing them by restricting background stimulation to the large inhibitory RF (IRF) surrounding the ERF. These results could be best accounted for by a double-opponent-process mechanism with both RF center and RF surround being directionally selective, but with opposite polarity. It is suggested that this type of mechanism could be involved in the processing of object motion.Partially supported by an NSERC University Research Fellowship (U 0057) and an ARC equipment grant to M. von Grünau and by an NSERC Grant to B. J. Frost (A 0353)