Corticopontine Cells Research Articles

Distribution in areas 18 and 19 of neurons projecting to the pontine nuclei: a quantitative study in the cat with retrograde transport of HRP-WGA.

Following large injections of horseradish peroxidase - wheat germ agglutinin in the pontine nuclei, corticopontine neurons in areas 18 and 19 were quantitatively mapped and flat maps showing the distribution of retrogradely labeled cells were constructed. The areal borders were defined either cyto- and myeloarchitectonically or from standard retinotopic maps presented in frontal sections (Tusa et al. 1981). Maps of the retinotopic organization in areas 18 and 19 (Tusa et al. 1979) were transferred to the present flat maps. Thus, the number and distribution of pontine projecting cells could be correlated with the retinotopic organization. The cell density (number of labeled cells per mm2 cortex) is in both areas highest in the cortex representing the lower and upper visual periphery and decreases towards the representation of the retinal central area. However, since in both areas 18 and 19 the visual field representation is twisted and portions of the visual field are magnified, the actual number of cells is higher in the cortex representing the central area and the lower medial visual field than in other parts. The cortex representing the lower hemifield contains approximately 2/3 (mean, N = 4) of the corticopontine cells in both areas. The average density of corticopontine cells increases from area 17 through 18 to 19, but the total number of cells within each of the areas is about the same (area 17: 18000 cells, area 18: 13400 cells, area 19: 17200 cells; mean, N = 4; data on area 17 from Bjaalie and Brodal, 1983). In conclusion, areas 17, 18 and 19 contribute about equally in quantitative terms to the pontine nuclei. Furthermore, assuming that the corticopontine neurons transmit spatially relevant information, there is a moderate overrepresentation of central vision and the lower medial visual field in the pontine projection from areas 18 and 19. This visual field representation is remarkably similar to that found in the corticopontine projection from area 17 (Bjaalie and Brodal 1983).

Distribution in area 17 of neurons projecting to the pontine nuclei: a quantitative study in the cat with retrograde transport of HRP-WGA.

The number and distribution of corticopontine neurons within area 17 of the cat were studied quantitatively with the use of retrograde transport of horseradish peroxidase-wheat germ agglutinin. Eight cats received stereotactic injections in the pontine nuclei; in three of these complete staining of the parts of the pontine nuclei receiving fibers from the visual cortex was achieved. Labeled cells were counted in frontal sections through the hemisphere, spaced at 0.5 mm. The borders of area 17 were determined cyto- and myeloarchitectonically and a flat map was produced for each animal. A map of the representation of the visual field in 10 degrees X 10 degrees blocks in the first visual area (Tusa et al., '78, '81) was transferred to our maps of area 17. The density and number of labeled corticopontine cells could then be determined within blocks of the cortex representing 10 degrees X 10 degrees of the visual field. The cell density (number of labeled cells per mm2 cortex) was found in general to be highest in parts of the cortex representing peripheral parts of the visual field. The cell density is low in cortex representing the central visual field, but the lowest density was found in the representation of a para-central region in the upper visual field. Furthermore, cortical regions representing the lower part of the visual field have a higher cell density than those representing the upper part; in four cases, 68-86% of all labeled cells were found in parts of area 17 representing the visual field below the horizontal meridian. Since there is an enlarged cortical representation of central vision, the much lower cell densities in "central" parts of area 17 than in "peripheral" parts may mean that all parts of the visual field are represented with equal numbers of corticopontine neurons ("linear" representation). This is not the case, however, since the number of labeled cells per 10 degrees X 10 degrees is considerably higher in the cortex representing the central 10 degrees and medial parts of the lower visual field than in the rest of area 17. Assuming that the corticopontine cells in the visual cortex transmit spatially relevant information, we conclude that there is an overrepresentation of central vision and the medial parts of the lower visual field in the corticopontine projection from area 17.

Cat visual corticopontine cells project to the superior colliculus

Antidromic stimulation was used to study corticopontine visual axons and their tectal collaterals in cats. Sixty-seven cortical cells were activated antidromically by electrical stimulation of the rostral pontine visual area, 38 in area 18, and 29 in lateral suprasylvian cortex. Two thirds of these corticopontine cells (46 cells) could also be antidromically activated by stimulation of the superior colliculus, demonstrating that they gave rise to a tectal collateral.

Cortical neurons projecting to the pontine nuclei in the cat. An experimental study with the horseradish peroxidase technique.

Horseradish peroxidase (HRP) injections in various portions of the cat pontine nuclei resulted in retrograde labeling of neurons in layer V of the ipsilateral cerebral cortex. Corticopontine neurons, pyramidal in type, have been found to be labeled in the entire cortex, confirming the previous findings of anterograde degeneration studies. Most (91%) of the labeled cells were 14--26 micrometer in diameter (mean 19.4 +/- 4.5 micrometer SD). Small (10--20 micrometer) and medium (20--40 micrometer) cells represent 51.5% and 47.7%, respectively, of the total number of the labeled neurons. The populations of the neurons of various sizes were almost identical in different cortical areas, and were different from the populations of corticoreticular and corticospinal cells. Corticopontine cells were well labeled in experimental cases of 3-days' survival time, confirming the topographical organization established previously by degeneration studies for this projection system. However, in cases of shorter survival time (20--27 h), the number of labeled neurons was very small. The relative paucity of labeled corticopontine neurons in the sigmoid and lateral gyri is discussed with reference to other cortical descending neurons (e.g., the corticotectal, corticoreticular and corticospinal) which have hitherto been identified morphologically as well as physiologically.

Cells of origin of corticopontine and corticotectal fibers in the medial and lateral banks of the middle suprasylvian sulcus in the cat. An experimental study with the horseradish peroxidase method

Cells of origin of corticopontine and corticotectal fibers in the medial and lateral banks of the cat middle suprasylvian sulcus (MSs area) were identified by means of the retrograde axonal transport of horseradish peroxidase. Somal diameters of labeled cells seen in the MSs area were measured after injection of the enzyme in the pons and the tectum. Diameters of corticopontine and corticotectal neurons are 12–35 μm (mean and SD: 18.9 ± 3.2 μm) and 12–55 μm (mean and SD: 27.7 ± 10.6 μm), respectively. These two kinds of neurons are both pyramidal in shape, located in layer V and the corticotectal neurons are, in general, larger and more polymorphic than the corticopontine cells. It thus appears that the two descending fibers originate from different, and independent sets of pyramidal neurons in layer V of the cortex.

Thalamic inputs and subcortical targets of cortical neurons in areas 5 and 7 of cat

Subcortical projection structures and thalamic inputs of single neurons in cortical areas 5 and 7 of cat were extracellularly investigated in locally anesthetized, encéphale isolé preparations and chronically implanted, behaving animals. Testing stimulations were applied to the lateralis intermedius (LI), lateralis posterior (LP), ventralis anterior (VA), and centrum medianum (CM) thalamic nuclei, the mesencephalic reticular formation, and the pontine nuclei. Output cells ( N = 101) were identified by antidromic invasion, selectively elicited in 91 cells from PN, CM, LI, or LP; the remaining 10 neurons had branching axons to two of the above targets. Two cortical-subcortical circuits involve areas 5 and 7. In one of them, afferents of LI and/or LP origin mainly reach cortico-CM cells and, less often, neurons giving rise to a reciprocal cortico-LI or cortico-LP projection, Within the other circuit, corticopontine cells are synaptically activated from the VA nucleus or convergently modulated from both the VA and LI nuclei. The unexpectedly high proportion of antidromically identified cells suggest that many functions of the parietal “association” cortex depend on downstream projections to the thalamic integrative nuclei and to the pontocerebellar system. Forty-two nonoutput cells were modulated synaptically, especially from the LI nucleus, with high-frequency spike barrages similar to activities described in putative interneurons recorded from other cerebral structures. The thalamically elicited excitation of nonoutput cells occurred immediately after the early discharges induced in output cells, in close time relation with secondary depth-negative waves and with the onset of a long-lasting slow positive shift associated with silenced firing in output cells.

Firing rates and patterns of output and nonoutput cells in cortical areas 5 and 7 of cat during the sleep-waking cycle

The rate and patterns of spontaneous discharge in output cells and putative interneurons of cortical areas 5 and 7 were analyzed in the behaving cat during wakefulness (W), synchronized (S) sleep, and desynchronized (D) sleep, with (D+) and without (D−) rapid eye movements (REMs). Output cells were antidromically identified following stimulation of the thalamic and pontine nuclei. Interneurons were inferred from their thalamically elicited synaptic responses consisting of high-frequency spike barrages. Non-parametric (rank) statistics were used for tests of significance. A method derived from the Wilcoxon rank tests was developed to permit some statistical testing between interspike interval histogram patterns. Rate analysis showed that output cells discharge in all states of the sleep-waking cycle at significantly higher rates than interneurons. Corticothalamic and corticopontine cells decreased firing rates from W to S sleep and reached maximal rates in both (D+ and D−) substates of D sleep. In contrast, interneurons increased firing rates from W to S sleep and had their highest rates in D sleep, selectively occurring during REM epochs. In output cells, pattern differences between states consisted essentially of: (a) more short and long interspike intervals in S sleep compared to W, which indicates an increase in the burst-silence pattern in S sleep; (b) more short, but less long, intervals in D sleep, compared to both W and S sleep, which results from tonic excitation during D sleep and indicates that the firing pattern in D sleep is not an extreme type of S sleep. Compared to output cells, interneurons in all states had more short and long intervals and a significantly higher probability of spike bursts. The REM-related firing of interneurons may be related to recent investigations suggesting the consolidation of memory traces during D sleep.

Corticopontine cells in area 18 of the cat.

1. Area 18 projects to the rostral pontine nuclei. The visual response properties of rostral pontine cells differ greatly from those that have been reported for area 18 cells. We identified and studied corticopontine cells in area 18 and compared their receptive-field properties to those of other area 18 cells and to pontine visual cells. 2. We first located the visual area in the rostral pons by microelectrode recording and placed stimulating electrodes at the same site. Anti-dromically invaded cells were then recorded in area 18. The antidromic invasion of each cell was verified by orthodromic-antidromic spike collision. 3. Fifty-seven well-isolated corticopontine cells were studied in detail. We also recorded 466 unitary antidromic potentials with a mean invasion latency of 3.5 ms and recorded from 40 additional area 18 units to serve as a comparison group for the corticopontine cells. The comparison group cells were located in the same area in the visual field as the corticopontine cells. 4. The average receptive-field area for corticopontine cells (485 deg2) was much larger than the comparison cells (59 deg2). Forty percent of the corticopontine cells responded preferentially to multiple-spot target. Properly oriented gratings, slits, or edges were the most effective stimuli for the comparison cells. Eighty-two percent of the corticopontine cells showed clear directional preferences to moving-spot stimuli, and downward movements were most commonly preferred. Fifty-five percent of the area 18 comparison cells showed some directional preference, but no particular direction was preferred. The optimal stimulus speeds for corticopontine cells were higher than those for the comparison cells. 5. The response properties of the area 18 corticopontine cells are similar to the response properties of rostral pontine visual cells, except for a somewhat higher selectivity for orientation in the corticopontine cells. 6. We conclude that most response properties of rostral pontine visual cells are already present in a subset of area 18 cortical cells which project to the pons. The corticopontine cells are sensitive to multiple-spot targets moving in particular directions over large portions of the visual field, such properties are consistent with a visuomotor function for the corticopontocerebellar pathway.

Single-unit recording and stimulation in superior colliculus of the alert rhesus monkey.

RECENT SINGLE-UNIT recording studies of the alert rhesus monkey superior colliculus have disclosed that the deeper layers of this structure contain cells which discharge in association with eye movement (15-17, 23, 24). Such units fire selectively prior to saccades of a specific direction and size, irrespective of the position of the eye in orbit. Stimulation studies of the superior colliculus have so far produced conflicting results. Some reports suggest that in the alert cat stimulation brings the eye to a certain position in orbit irrespective of eye position prior to stimulation (1, 9, 19). Thus, the size and direction of elicited saccades is reported to vary as a function of initial eye position. By contrast, in the alert monkey it has recently been reported that stimulation produces conjugate saccades of a specific size and direction; these parameters are the same no matter where the eye is in the orbit prior to stimulation (12, 15, 16). The stimulation map of Robinson (12) shows a reasonable correspondence with the receptive-field map of the superior colliculus reported by Cynader and Berman (5). The aim of this study was to clarify the relationship between recording and stimulation data by using methods which allow a direct comparison. We used alert rhesus monkeys which had one eye immobilized for the mapping of visual receptive fields. The other eye was normal, thus permitting the study of eye movement. Stimulation and recording were carried out using the same low-resistance microelectrode; for each site sampled, records were obtained for both single-unit activity and for electrical stimulation.

Activity of superior colliculus in behaving monkey. IV. Effects of lesions on eye movements.

Activity of superior colliculus in behaving monkey. IV. Effects of lesions on eye movements.

RECEPTIVE FIELDS AND FUNCTIONAL ARCHITECTURE IN TWO NONSTRIATE VISUAL AREAS (18 AND 19) OF THE CAT.

RECEPTIVE FIELDS AND FUNCTIONAL ARCHITECTURE IN TWO NONSTRIATE VISUAL AREAS (18 AND 19) OF THE CAT.