1. The primary goal of this study was to characterize the information about single-joint forelimb movements supplied to intermediate cerebellar cortex by mossy fibers. Discharge of mossy fibers and Golgi cells was studied while monkeys operated six devices that required movements about specific joints. Additional control experiments in anesthetized cats and monkeys established criteria for identification of mossy fibers and Golgi cells. 2. The control experiments demonstrate that mossy fibers can be distinguished from Purkinje and Golgi cells by the waveshapes of their action potentials. Asynaptic activation from the inferior cerebellar peduncle, in combination with histological localization of recording sites in granular layer or subcortical white matter, verified that mossy fibers produce a variety of waveshapes that are characterized by brief initial phases and relatively small amplitudes. The same waveshapes were observed for the mossy fiber recordings from awake monkeys, and many identified mossy fibers had sensory properties similar to those found in the awake animals. From these combined criteria, we conclude that the recordings in the awake animals were from mossy fibers. Golgi cells, recorded exclusively in the granular layer of cerebellar cortex, were characterized by action potentials of longer duration and larger amplitude as compared with mossy fibers, and none were asynaptically activated from the inferior cerebellar peduncle. 3. Units were isolated while the monkeys made free-form and tracking movements. We studied movement-related discharge of 80 mossy fibers and 12 Golgi cells. Mossy fibers showed high modulations during use of at least one of the six manipulanda and had clear preferences for movement about a specific joint, although they often showed consistent but weaker firing during movement about a neighboring joint. Separation of movements by more than one joint produced a large reduction in discharge: shoulder units never fired well to movements of the finger, and finger units never fired well to movement of the shoulder. 4. The tracking task required maintenance of fixed limb positions (a static phase) as well as movements between these positions (a dynamic phase). Of 80 mossy fibers, 18% had purely tonic discharge patterns, 63% were phasic-tonic, and 20% were purely phasic. Discharge patterns were reciprocal (45%), bidirectional (42%), or unidirectional (13%). 5. Eighty percent of the mossy fibers exhibited tonic discharge that was significantly (P < 0.01) correlated with joint angle (r = 0.65 +/- 0.19, mean +/- SD), and about one third had phasic components that were significantly correlated with movement velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Movement-related inputs to intermediate cerebellum of the monkey

The central projections of the rat sciatic, saphenous, median, and ulnar nerves were labeled by injecting each nerve with 0.05 mg B-HRP, or 0.5 mg WGA-HRP, or a mixture of both. The B-HRP labeled large dorsal root ganglion cells (30-50 microns) and, correspondingly, 98% of axons labeled in a rootlet were meyelinated; although all sizes of myelinated axons were labeled, a greater proportion fell in the large ranges (2-6.5 microns axon diameter) than in the small ranges (0.5-2 microns). Primary afferents labeled with B-HRP were distributed in laminae I, III, IV, and V of the dorsal horn and extended into the intermediate grey and the ventral horn; Clarke's column and the respective dorsal column nuclei were also densely labeled. Motoneurons of the nerve were densely labeled by B-HRP, including extensive regions of their dendritic trees. In contrast, WGA-HRP labeled small dorsal root ganglion cells (15-25 microns) and in the dorsal rootlets, 84% of the labeled axons were nonmyelinated; the small population of labeled myelinated afferents mainly fell within the smaller ranges (0.5-2.0 microns). Terminal fields of WGA-HRP labeled afferents were restricted to the superficial dorsal horn (laminae I-III), and to limited regions in the dorsal column nuclei. Sciatic nerve projections traced by labeling with B-HRP alone or in combination with WGA-HRP were more extensive than previously described when using either native HRP or WGA-HRP. Afferents to the dorsal horn extended from L1-S1, to Clarke's nucleus from T8-L1, to the ventral horn from L2-L5, and extended throughout the medial and dorsal region of the gracilie nucleus. Motoneurons were found from L4-L6. Using the same tracers, saphenous projections extended in the superficial dorsal horn from caudal L1 to rostral L4, in the deep dorsal horn to mid L4 and along the length of the central part of the gracilie nucleus. The median nerve projected to the internal basilar nucleus from C1-C6, the dorsal horn from C3-T2, Clarke's nucleus from T1-T6, the external cuneate nucleus, and a large central area throughout the length of the cuneate nucleus. Motoneurons were located in dorsolateral and ventrolateral nuclear groups from C4 through C8. The ulnar nerve projections were less extensive but also included the internal basilar nucleus from C1-C6, the medial region of the dorsal horn from C4-T1, Clarke's nucleus from T1-T6, the external cuneate nucleus, and the medial part of the cuneate nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Central projections of the sciatic, saphenous, median, and ulnar nerves of the rat demonstrated by transganglionic transport of choleragenoid-HRP (B-HRP) and wheat germ agglutinin-HRP (WGA-HRP)

Output systems of the dorsal column nuclei in the cat.

Central termination patterns of primary afferents from the hand and forelimb were studied following subdermal injections of HRP conjugates in macaque monkeys. In the middle layers of the dorsal horn of the spinal cord, afferents from digits 1–5 terminated in a rostrocaudal sequence in separate, elongated columns at cervical levels 5–7. Afferents from teh glabrous digits extended to the medial margin of the dorsal gray, while afferents from the dorsal skin of the digits terminated more laterally. Afferents from the dorsal hand and palm terminated lateral to those from the digits, while inputs from the forearm occupied tissue rostral and caudal to the representation of the hand. In the cuneate nucleus, terminations from each digit formed an elongated column that was densely labelled in the central pars rotunda and sparsely labelled in both the rostral and caudal reticular poles. Within the pars rotunda, digits 1–5 were represented in order from lateral to medial. Inputs from the digit tips terminated ventral to inputs from the proximal digits. Afferents from the dorsal skin of the digits terminated in an even more dorsal position, while the most dorsal portion of the pars rotunda related to the glabrous and dorsal hand. Within the pars rotunda, terminations from specific parts of the hand overlapped parcellated clusters of neurons. These clusters were densely reactive for cytochrome oxidase (CO) and were surrounded by myelinated fibers. Much sparser label in the reticular poles was found consistently only after injections in the glabrous digits. Inputs to the poles appeared diffuse and overlapping while preserving some somatotopic order. When treated for CO or stained for Nissl substance or myelin, the pars rotunda of humans showed parcellation patterns that closely resembled the patterns seen in monkeys. From the relationship of inputs to the CO dense cell clusters in monkeys, it was possible to postulate in detail the somatotopic organization of inputs to pars rotunda of humans.



The present results provide a comprehensive description of the somatotopic patterns of termination of afferents from the skin of the hand and forearm in the spinal cord and cuneate nucleus of macaque monkeys. A direct relationship of afferent somatotopy and identifiable cell clusters in the pars rotunda of the cuneate nucleus is further demonstrated. Finally, the patterns of cell clusters in the pars rotunda of macaque monkeys and humans suggest that the somatotopic organization of the cuneate nucleus may be very similar in human and nonhuman primates.

Somatotopic organization of inputs from the hand to the spinal gray and cuneate nucleus of monkeys with observations on the cuneate nucleus of humans.

Nineteen physiologically identified group Ia and five group Ib fibers at the L3 and L4 levels of the spinal cord originating from various hind-limb muscles were intraaxonally injected with horseradish peroxidase (HRP). The trajectories of the stained axons were reconstructed. They extended for distances of 8.6 mm-18.0 mm rostrocaudally. Ascending axons ran in various regions of the dorsal funiculus: The ascending axon from a toe muscle (3 microns in diameter) ran in the ventral most part of the paramedian region; those from shank muscles (3.0-5.0 microns) in both dorsal and ventral paramedian regions; those from thigh muscles (5.0-7.0 microns) in both the paramedian and the more lateral regions; and those from hip muscles (6.0-7.0 microns) in the lateral region. Main collaterals arising from the parent fiber were given off at intervals of 0.5-6.2 mm (mean 2.4 mm). Collaterals of a fiber from a toe muscle (1.0 micron in diameter) entered Clarke's column from the dorsomedial side and ramified mostly in the dorsomedial one-third of the column. Collaterals of fibers from shank muscles (1.0-2.0 microns) entered Clarke's column from the dorsal side and terminated in its middle parts as well as in laminae V-VII. Collaterals of fibers from thigh muscles (1.0-2.5 microns) passed lateral to or through the lateral part of Clarke's column and terminated in its ventrolateral part and in laminae V-VIII. Collaterals of fibers from hip muscles (1.5-2.5 microns) passed lateral to Clarke's column and ramified mostly in laminae VII-IX. As the muscle of origin became more proximal, the proportion of termination outside of Clarke's column progressively increased. Thus, the trajectory of group I fibers was somatotopically organized both in the dorsal funiculus and in the gray matter. The long axis of boutons ranged from 0.5 to 17 microns in Ia fibers and from 0.5 to 8 microns in Ib fibers. "Giant" Ia boutons (above 7 microns) were found both in and outside Clarke's column.

Trajectory of group Ia and Ib fibers from the hind-limb muscles at the L3 and L4 segments of the spinal cord of the cat.

Muscular and cutaneous afferents from distal forelimb distributed to the cuneate and external cuneate nuclei have been demonstrated in cat with the method of transganglionic transport of horseradish peroxidase. Injections of the same tracer were also done in ganglia C7 to T6 to demonstrate the afferents to these two nuclei. It is concluded that only muscle afferents terminate in the external cuneate nucleus. Afferents from paw and forearm occupy sequential territories in the medial part of the nucleus, which are only partly exclusive. Afferents from individual flexor muscles of forearm occupy distinct sites but their distributions overlap with those of forearm extensor muscles. In the external cuneate nucleus, the, distributions of afferents from individual muscles constitute integral parts of a segmental representation. In the cuneate nucleus, cutaneous afferents are located dorsally and terminate over cells of the “clusters”. Muscle afferents are distributed in ventral regions and are topographically arranged. They terminate over “reticular” regions.

Afferent projections from forelimb muscles to the external and main cuneate nuclei in the cat. A study with transganglionic transport of horseradish peroxidase.

L. Jasmin

Papers

Afferent projections from forelimb muscles to the external and main cuneate nuclei in the cat. A study with transganglionic transport of horseradish peroxidase.