Cerebellar afferents from the trigeminal sensory nuclei in the cat

Summary The cerebellar afferent projection from the trigeminal sensory nuclei (TSN) was studied by means of retrograde axonal transport of horseradish peroxidase (HRP). The projection is almost exclusively ipsilateral. Three cortical regions, viz., the intermediate-lateral part of lobulus simplex with the adjacent area of lobule V, the rostralmost folia of the paramedian lobule with the surrounding parts of crus I and II, and lobule IX, especially its rostral two folia, are the main targets for the cerebellar afferent fibres. A few fibres reach also the other cerebellar regions, as shown in Fig. 3.Most of the cerebellar afferent fibres originate in the nucleus interpolaris with nucleus oralis as the second most important region. The projection from the principal nucleus is moderate and reaches primarily the area of the crura bordering on the paramedian lobule and lobule IX. The projections from the nucleus caudalis and nucleus mesencephalicus are scanty. The fibres from the latter reach only the vermal region.The findings are discussed in relation to previous anatomical and physiological observations.On leave from the Laboratory of Neurobiology and Department of Anatomy, Faculty of Science, Mahidol University, Bangkok, Thailand, under the Fellowship Program of the Norwegian Agency for International Development (NORAD)     

The lateral reticular nucleus in the cat IV. Activation from dorsal funiculus and trigeminal afferents

1. The activation of neurones in the mLRN (major portion of lateral reticular nucleus comprising its parvi- and magnocellular parts) be a spinal path ascending in the dorsal funiculus (DF) and by trigeminal afferents has been studied. 2. Stimulation of the DF at C3 activated about one half of the mLRN neurones. The latencies were 2-28 ms. In experiments with the spinal cord interrupted at C3 except for the DF it was shown that cutaneous and high threshold muscle afferents in mainly forelimb nerves were effective. The latencies of the responses to nerve stimulation were 8-27 ms. 3. Stimulation of trigeminal afferents evoked a response in about one third of the mLRN neurones. The latencies were 2-27 ms. 4. Activation from the DF- and trigeminal paths occurred often in the same mLRN neurones and the neurones activated from the two paths had a similar location in the nucleus and a similar termination in the cerebellar cortex. 5. The DF- and trigeminal paths had similar properties. Activation was evoked from both ipsilateral and contralateral nerves. Fast adapting hair receptors were commonly effective. 6. Evidence is presented indicating that the DF- and trigeminal paths share a common final path to the mLRN neurones which is formed by brain stem interneurones intercalated between the DF- and trigeminal nuclei and the mLRN. It is suggested that these interneurones represent a supraspinal motor centre. 7. Activation from the DF- and trigeminal paths occurred with unequal frequency among groups of mLRN neurones activated from different spinal paths ascending in the ipsilateral lateral funiculus (cf. Clendenin et al., 1974a).     

Functional organization of long,second-order afferents in the dorsal funiculus

Summary Second-order neurones activated from forelimb nerves and ascending in the deep part of the dorsal funiculus from the eighth to the first cervical segentm were investigated in the cat by axonal recording. These neurones form a previously unknown tract denoted the ascending dorsal funiculus tract, ADFT. The ADFT neurones receive excitation from cutaneous afferents as well as high threshold afferents in deep nerves. The excitation is supplied by afferents from hair, touch, and possibly also pain receptors in the skin, and from receptors in deep connective tissue. There is no excitation from muscle spindles or from specific joint receptors. The cutaneous receptive fields are small and lack inhibitory surround.     

Dorsal column nuclei afferents in the lateral funiculus of the cat: Distribution pattern and absence of sprouting after chronic deafferentation

Summary In adult cats the successive degeneration technique has been used to demonstrate the existence and distribution pattern of lateral funicular fibers to the dorsal column nuclei (DCN) originating from the brachial and thoracic cord. In a first operation, interruption of the dorsal columns at appropriate cervical levels and of the lateral funiculus at low thoractic levels was performed. Thirteen months later, a lesion was made in the lateral funiculus at upper brachial or uppermost thoracic levels. Fiber degeneration in the DCN consequent to this second operation is not contaminated by damage to dorsal roots or by interruption of lateral funicular afferents from lumbo-sacro-coccygeal segments. All animals were sacrified 7 days after the second operation. Serial sections through the medulla oblongata, impregnated with the Fink-Heimer technique, show that fibers ascending from brachial levels in the dorsal part of the lateral funiculus reach the cuneate nucleus either by a dorsomedial route through the tegmentum or by ascending in the restiform body. Degenerated fibers distribute selectively to the rostral part, and to a lesser extent to the base, of the cuneate nucleus. Only very few fibers ascending from thoracic levels in the lateral funiculus distribute to the DCN.Abbreviation List CUN cuneate nucleus - DV dorsal motor nucleus of vagus nerve - EC external cuneate nucleus - GR gracile nucleus - HYP hypoglossal nucleus - int nucleus intercalatus - PH nucleus praepositus hypoglossi - PM paramedian nucleus - SOL solitary nucleus and tract - VEST vestibular complex - X nucleus X of Brodal and Pompeiano (1957) - Z nucleus Z of Brodal and Pompeiano (1957) - V spin spinal trigeminal nucleus     

Tectorecipient zone of cat lateral posterior nucleus: evidence that collicular afferents contain acetylcholinesterase

Summary The superficial layers of the cat's superior colliculus innervate the medial subdivision of the thalamic lateral posterior nucleus (LPm). LPm is set off from adjoining thalamic zones by its denser staining for acetylcholinesterase (AChE). We sought to learn whether the tectal afferents to LPm might themselves be the source of the enzyme staining by examining the effects of collicular lesions on the thalamic staining pattern. Large excitotoxin lesions of the colliculus largely eliminated AChE staining in the ipsilateral LPm. By contrast, fibersparing lesions of LPm itself left AChE staining nearly unchanged. Destruction of collicular neurons by excitotoxins dramatically reduced AChE staining in fibers of the brachium and superficial gray layer of the superior colliculus. The reduction was especially pronounced in the lower part of the superficial gray layer, in which LP-projecting collicular neurons are located. These results are consistent with the view that LP-projecting collicular neurons synthesize AChE and account for much of the histochemically detectable enzyme present both in the lower superficial gray layer and in LPm. In the colliculus, the excitotoxin lesions spared AChE staining in a thin sheet at the upper border of the superficial gray layer and in the enzyme-positive patches in the intermediate layers. This surviving tectal AChE thus is probably presynaptic and could be contained at least partly in cholinergic afferents from the parabigeminal nucleus and pontomesencephalic tegmentum. The collicular lesions had no obvious effect on AChE staining in the parabigeminal nucleus or in the C-laminae or ventral division of the lateral geniculate nucleus.     

Myelin breakdown in the posterior funiculus of the kitten after dorsal rhizotomy

Summary Morphological aspects of myelin breakdown in the posterior funiculus during Wallerian degeneration were studied in kittens subjected to lumbosacral dorsal rhizotomies 6–8 days after birth. The first sign of myelin breakdown was characterized by swollen or shrunken nerve fibers. Shortly thereafter there was an increased occurrence of collapsed myelin sheaths and later of rounded myelin bodies. Myelin was clearly seen in microglial cells. Correlative observations on Marchi-stained material indicated the simultaneous and frequent appearance of Marchi-positive bodies (MPB:s) and myelin bodies. Due to the rapidity of the degeneration process in the kitten, the increase in the occurrence of Marchi-positive granules (MPG:s) seemed to start concomitantly with increased occurrence of MPB:s. However, the frequent occurrence of MPG:s outlasted that for MPB:s. The findings indicate that the MPB:s may be the counterpart to myelin bodies and the MPG:s to lipid droplets. Microglial cells may be responsible for the primary uptake of degenerating myelin and the subsequent transformation of myelin bodies to lipid droplets. The much faster breakdown of myelin and elimination of lipid material in the degenerating posteror funiculus of the kitten, as compared to the adult, seemed to be due not only to the lower myelin content in the kitten, but also to a higher density of microglia and a greater efficiency in the myelin breakdown process in the degenerating posterior funiculus of the kitten.     

Thalamic projection of muscle nerve afferents in the cat

1. Evoked responses on stimulation of hind- and forelimb muscle nerves have been recorded in the ventro-postero-lateral (VPL) and centre median (CM) nuclei of the thalamus of the cat.2. The stimulation of hind-limb muscle afferents with increasing strength usually did not evoke a thalamic response, either in the CM or in the VPL, until the threshold for Group III muscle afferents was reached.3. Short latency potentials were evoked in the VPL on stimulation of low threshold Group I muscle afferents from forelimbs. The projection zone occupies the dorso-medio-rostral part of the nucleus.4. An attempt was made to locate the medullary relay for forelimb Group I afferents either in the lateral part of the cuneate or in external cuneate.5. Low threshold afferents from forelimb muscle nerves do not project to the CM. CM responses began to appear only when the threshold for Group II muscle nerve fibres was reached.6. Group II afferents from hind- or forelimb muscle nerves projecting to the CM are probably not connected to spindle secondary endings.7. The role played by muscle afferents in the somesthetic mechanisms is briefly discussed.     

Olivary afferents from the pretectal nuclei in the cat

Summary The organization of the projection from the pretectal region to the inferior olive in the cat was studied by means of retrograde protein tracing and experimental degeneration. Small injections of horseradish peroxidase (HRP) were made into various parts of the inferior olive from a ventral approach. The number of nerve cells in the pretectal nuclei retrogradely labelled with HRP was counted and put in relation to the site of injection. Labelled cells were only found in the posterior pretectal nucleus (NPP), the nucleus of the optic tract (NOT) and the anterior pretectal nucleus (NPA). Most labelled cells were found in NPP and NOT in cases in which the rostral or caudal levels of the principal olive were labelled by the injection. NAP labelling occurred in one case with a very rostral injection of the inferior olive. Unilateral electrolytical destruction of the pretectal region produced terminal degeneration in the ipsilateral inferior olive. The heaviest ipsilateral degeneration was found in the upper half of the principal and dorsal accessory olives, and caudally in the ventrolateral outgrowth, the dorsal cap and nucleus with the adjacent part of the medial accessory olive. Some functional implications of the findings are discussed.     

Morphometric evaluation of posterior funiculus nerve fibers in relation to aging

We morphologically evaluated the size of axons in the posterior funiculus in different age groups and examined the changes due to aging. In the past, such studies have been conducted at the cervical spinal cord (C6) level, and a decrease in the size and number of axons due to aging has been noted. The current study was conducted at the lower lumbar spinal cord (L2) level.     

The projection of splanchnic afferents on the cerebellum of the cat

1. The projections of the ipsilateral and contralateral splanchnic nerves on the cerebellum were studied in cats under sodium thiopentone anaesthesia.2. The splanchnic nerves were electrically stimulated. Evoked potentials and single unit discharges were recorded by means of 2.5 M-NaCl-filled glass micropipettes. A responsive region was found in the intermediate cortex of lobules Vb to f of the anterior lobe.3. The Agammadelta fibres of the splanchnic nerve had a bilateral cerebellar representation. The Abeta fibres were represented only on the ipsilateral side.4. At the level of the upper cervical spinal cord, fibres from the ipsilateral splanchnic nerve were conveyed in both the dorsal and lateral funiculi; fibres from the contralateral nerve were restricted to the ipsilateral lateral funiculus.5. On the basis of the characteristic potential fields generated in the cerebellar cortex, it is concluded that the majority of the splanchnic afferents studied terminate in the cerebellum as climbing fibres. A few responses of short latency may have been due to a mossy fibre input.6. In interaction experiments, a conditioning stimulus to one splanchnic nerve depressed the response to stimulation of the other nerve for up to 80-100 msec, the effect being most pronounced at 40-50 msec. During this period, spontaneous activity of the cerebellar unit was also suppressed.7. The organization of the splanchnic pathways to the cerebellum and their terminal connexions are discussed.     

Characterization of pretectal-nuclear-complex afferents to the pulvinar in the cat

We investigated anatomical and physiological properties of the projection from the pretectal nuclear complex (PNC) to the ipsilateral lateral posterior–pulvinar complex in the cat. After Phaseolus vulgaris leucoagglutinin injections into the PNC, the majority (70%) of anterogradely labeled terminals was localized in the pulvinar proper, the remaining 30% were scattered in the lateral and medial portions of the LP. No PNC neuron retrogradely labeled from the pulvinar was found to also express glutamic acid decarboxylase (GAD) mRNA, although a large number of neurons carrying the GAD label were found in close vicinity. In contrast, 69% of retrogradely labeled PNC cells also displayed glutamate-like immunoreactivity. Twenty-six out of 96 (27%) visually responsive pulvinar neurons were orthodromically activated by electrical stimulation of the ipsilateral PNC at latencies between 1 and 10 ms (median 1.9 ms). All orthodromically activated neurons responded well to the onset and offset of large visual stimuli and to sudden stimulus shifts. Whenever a saccadic eye movement was executed, these neurons were also activated, except during saccades in darkness. The comparison of saccade-evoked response with responses to visual stimuli that elicit similar retinal image shifts revealed that pretectorecipient pulvinar neurons also seem to receive a saccade-related non-visual input. All response properties correspond to those of a specific class of pulvinar neurons that have been termed "SV" neurons because they respond to visual stimulation as well as during saccades. They also closely resemble response properties of PNC neurons that project to the ipsilateral pulvinar. The results support the proposal that PNC cells not only directly activate their postsynaptic target neurons in the pulvinar, but that they also provide a visual input to these neurons that greatly contributes to their response characteristics. Electronic Publication     

Chemical ablation of sensory afferents in the walking system of the cat abolishes the capacity for functional recovery after peripheral nerve lesions

Weakening the ankle extensor muscles of cats by denervation of the synergists of the medial gastrocnemius (MG) muscle results in transient increase in yield at the ankle during early stance. Recovery of ankle function occurs over a period of 1–2 weeks, is use-dependent, and is associated with increases in the strength of reflexes from MG group I muscle afferents and an increase in the magnitude of bursts in the MG muscles during stance. These observations have led to the hypothesis that feedback from large muscle afferents is necessary for functional recovery. In this investigation we have tested this hypothesis by examining functional recovery in animals treated with pyridoxine, a drug known to destroy large muscle afferents. In four adult animals we confirmed that pyridoxine abolished the group I-mediated tendon-tap reflex in the ankle extensor muscle, and subsequently found that group I afferents from MG were either destroyed or non-conducting. Immediately after pyridoxine treatment the animals showed severe locomotor dysfunction but all recovered significantly over a period of 1 or 2 months and showed only minor kinematics deficits at the time of the muscle denervations. In all four pyridoxine-treated animals, weakening of the ankle extensors by denervation of the synergists of the MG muscle resulted in a large increase in yield at the ankle that persisted almost unchanged for a month after the operation. The magnitude of burst activity in the MG muscle during early stance of the pyridoxine-treated animals either did not increase or increased only slightly after the denervation of synergists. These observations are consistent with the hypothesis that feedback from group I afferents is necessary for functional recovery in untreated animals. Electronic Publication     

Mechanical sensitivity of group III and IV afferents from posterior articular nerve in normal and inflamed cat knee

Recordings were performed from sciatic nerve or dorsal root filaments in 28 cats to study single group III (conduction velocity 2.5-20 m/s) and group IV (conduction velocity less than 2.5 m/s) units supplying the knee joint via the posterior articular nerve (PAN). In seven of these cats the knee joint had been inflamed artificially. Recordings from sciatic nerve filaments revealed responses to local mechanical stimulation of the joint in only 3 of 41 group IV units and in 12 of 18 group III units from the normal joint. In the inflamed joint 14 of 36 group IV units and 24 of 36 group III units were excited with local mechanical stimulation. In recordings from dorsal root filaments (normal joint) 4 of 11 group IV units and 7 of 13 group III units were activated by stimulating the joint locally. In the normal joint four group IV units (recorded from dorsal root filaments) responded only to rotations against the resistance of the tissue, whereas the majority of the fibers did not respond even to forceful movements. Group III units with local mechanosensitivity in the normal joint reacted strongly or weakly to movements in the working range of the joint or only to movements against resistance of the tissue. In the inflamed joint, group IV fibers (recorded in sciatic nerve filaments) with detectable receptive fields responded strongly to gentle movements or only to movements against resistance of tissue. Some did not react to movements. Group III units reacted strongly or weakly to gentle movements or only to movements against resistance of the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)