Progressive supranuclear palsy with asymmetric lesions in the thalamus and cerebellum,with special reference to the unilateral predominance of many torpedoes

This report concerns a notable case of progressive supranuclear palsy exhibiting asymmetric dentate nucleus and thalamic degeneration with numerous torpedoes. The neuronal loss in the ventral lateral nucleus of the thalamus was predominant on the right side, while in the cerebellum, a quantitative study revealed the contralateral predominance of the neuronal loss in the dentate nuclei and torpedo formation, with preserved Purkinje cells. The abnormal tau-protein-related profiles in the two nuclei did not show any laterality in their distribution, indicating that the dentatothalamic tract may have been affected in a non-specific way in this case. In addition, the fact that the prominent sites of torpedo formation and loss of dentate nucleus neurons are identical supports the hypothesis that the torpedoes may be formed in association with neuronal loss in the dentate nucleus because of a plausible metabolic change in Purkinje cells through synaptic detachment of their axon terminals. Received: 4 January 1996 / Revised: 27 March 1996 / Accepted: 5 April 1996     

Isolated angiitis of the central nervous system: involvement of penetrating vessels at the base of the brain

Summary Isolated angiitis of the central nervous system (IAC) was diagnosed in a 40-year-old Caucasian male by histological examination of a leptomeningeal biopsy specimen, and the exclusion of systemic inflammatory or infective disease. Therapy with prednisone 30 mg/day and cyclophosphamide 100 mg/day resulted in clinical and radiological improvement, which have been maintained for an 8-month follow-up period. Magnetic resonance imaging (MRI) showed lesions implicating involvement of specific penetrating vessels at the base of the brain, an unusual complication of IAC, and allowed an accurate MRI-clinical correlation.     

Thermoreceptive lamina I trigeminothalamic neurons project to the nucleus submedius in the cat

Summary The technique of antidromic mapping with a roving array of electrodes was used to demonstrate that lamina I trigeminothalamic cells responsive specifically to skin temperature project to the n. submedius (Sm) in the medial thalamus of the cat. This finding indicates that Sm receives thermoreceptive in addition to nociceptive information.     

Noxious stimuli excite neurons in nucleus submedius of the normal and arthritic rat

Anatomical studies have revealed the existence of an ascending pathway originating in the spinal cord and medullary dorsal horn, relaying in nucleus submedius (Sm) in medial thalamus and terminating in ventrolateral orbital cortex. It has been suggested that this pathway may be involved in the transmission of nociceptive information. In the present study extracellular recordings were obtained from neurons in Sm of anesthetized arthritic and normal rats. Mechanical and thermal stimuli were delivered to various regions of the body to determine the types of somatic stimuli which could activate Sm neurons. Over 40% of the 146 neurons studied responded to somatic stimuli. In the normal rats only high intensity mechanical and thermal stimuli were effective in inducing responses. In the arthritic rats lower intensity mechanical stimuli, joint movements and high intensity thermal stimuli were effective. Such stimuli produce nociceptive reactions in the freely moving arthritic rat. Almost all the responses were excitatory and generally lasted the entire duration of the 15-s stimuli employed. In some cases after-discharges were present. The receptive fields of the neurons were in almost all cases large and bilateral. These findings support the hypothesis that Sm may be involved in mediating the affective-motivational aspects of pain.     

The organization of trigeminotectal and trigeminothalamic neurons in rodents: a double-labeling study with fluorescent dyes

Retrogradely transported fluorescent dyes (fast blue and diamidino-dihydrochloride yellow) were used to compare the distributions of trigeminofugal neurons that project to the superior colliculus and/or the thalamus in three rodent species. The objective was to determine what the projection and collateralization patterns of these trigeminofugal pathways are and whether they are similar among different species. In each anesthetized animal, one dye was injected into the superior colliculus and the other into the topographically congruent area of the thalamus. Counts of the numbers of yellow, blue, and double-labeled neurons were made throughout the trigeminal complex: principalis, pars oralis, pars interpolaris, and pars caudalis. Trigeminothalamic projections were similar in each of the rodent species studied. The densest concentration of retrogradely labeled neurons was in principalis, with substantially fewer neurons in pars interpolaris, and fewer still in pars oralis and pars caudalis. These neurons were generally small and tended to have round or fusiform somata. A common pattern was also noted among the three species for trigeminotectal neurons. Most trigeminotectal projections originated from neurons in pars interpolaris, somewhat fewer from pars oralis, and the fewest from principalis and pars caudalis. These neurons tended to be the largest in each subdivision and were often multipolar. Following paired injections of the tracers, double-labeled neurons were scattered throughout the sensory trigeminal complex and had morphologies characteristic of single-labeled trigeminotectal neurons. Although comparatively few double-labeled neurons were observed in any species, most of those seen were restricted to the ventrolateral portion of pars interpolaris, a position that corresponds to the representation of the vibrissae. These data indicate that, regardless of the rodent species, the vast majority of labeled trigeminal neurons project either to the superior colliculus or the thalamus, but not to both targets. This might be expected on the basis of the very different behavioral roles these structures play. On the other hand, a subpopulation of trigeminal neurons exists (mainly in pars interpolaris) that does project to both the superior colliculus and the thalamus, perhaps because both structures require some of the same somatosensory information to perform their behavioral functions.     

Electrophysiologic studies on the pallido- and cerebellothalamic projections in squirrel monkeys (Saimiri sciureus)

Summary Thalamic projections of the pallidum and the deep cerebellar nuclei were studied by unitary recordings as well as field potential analysis in the thalamus of squirrel monkeys (Saimiri sciureus) under sodium pentobarbital anesthesia.Stimulation of the pallidum produced a positive field potential preceded by incoming afferent fiber volleys in the thalamus. Spontaneous discharges of thalamic neurons were suppressed during this positive potential, and intracellular recordings from the thalamic neurons revealed that the time course of this field potential corresponded to that of the hyperpolarizing potential. The hyperpolarization was presumed to be a monosynaptic inhibitory postsynaptic potential by the short synaptic delay (about 0.5–0.7 ms) and responsiveness to high frequency stimulation (over 150 Hz). The positive field potential on stimulation of the external pallidal segment was distributed in L.po (VA) and the reticular thalamic nucleus around L.po, whereas that on stimulation of the internal segment was in V.o.a (the anterior basal part of VL) and in Z.o (upper part of VL). The projection of the external segment appeared to be less dense than that of the internal segment.The projection of deep cerebellar nuclei was situated in V.o.a, V.o.p (posterior part of basal part of VL), V.o.i (VLm), the intralaminar nucleus (CL), and some part of V. im (the rostral part of VPLo). Projections of the interpositus and dentate nuclei were distributed in a more anterior part than those of the fastigial nucleus. A certain topographical arrangement of the projections of these three nuclei was found in V.o.p, V.o.i and V.im. No significant overlap was detected between projections of the pallidum and the deep cerebellar nuclei within the thalamus.     

Retinal projections to the lateral posterior-pulvinar complex in intact and early visual cortex lesioned cats

In intact cats, it is generally considered that the lateral posterior-pulvinar complex (LP-pulvinar) does not receive direct retinal terminals, with the exception of the retino-recipient zone known as the geniculate wing. There is, however, some evidence that early lesions of the visual cortex can occasionally induce the formation of novel retinal projections to the LP nucleus. Given the importance of knowing the connectivity pattern of the LP-pulvinar complex in intact and lesioned animals, we used the B fragment of cholera toxin, a sensitive anterograde tracer, to reinvestigate the retinal projections to the LP-pulvinar in normal cats and in cats with early unilateral lesions of the visual cortex (areas 17 and 18). Immunohistochemical localization of the toxin was performed to show the distribution and morphology of retinofugal terminals. A direct bilateral but predominantly contralateral retinal projection reached the caudal portion of LPl and LPm in the form of patches located mainly along its dorsomedial surface and many scattered terminals. The distribution of retinal projections to LP-pulvinar in intact and operated cats did not differ. Contrary to what had been previously reported, we found no evidence for lesion-induced sprouting of retinal axons in these higher-order thalamic nuclei. Retinal input to the LP-pulvinar might modulate visual responses driven by primary visual cortex or superior colliculus.     

Muscarinic action of acetylcholine in the rat ventromedial thalamic nucleus

Summary Several lines of evidence suggest a role for ACh in the mediation of cerebello-thalamic transmission. The physiological, pharmacological and biochemical experiments described were designed to test this hypothesis for the rat cerebello-thalamic pathway. Unilateral electrolytic lesions of the superior cerebellar peduncle resulted in modest falls of CAT from both ventromedial thalamic nuclei (contralateral 35%, ipsilateral 15%). Iontophoretic application of ACh to relay cells evokes three types of response (i) excitation (ii) inhibition (iii) polyphasic combinations of (i) and (ii). The type of response evoked was directly related to the firing pattern of the cell. Thus, for example, excitatory responses were never recorded during high-frequency bursting but were easily evoked following a switch to tonic, single-spike activity. All responses to ACh and synaptic responses to cerebellar stimulation were sensitive to muscarinic but not to nicotinic cholinergic antagonists. The nicotinic antagonist mecamylamine was a potent blocker of excitant amino acid responses but had no effect on cerebellarevoked synaptic responses. Cholinergic and anticholinergic agents had a profound action on relay cell firing pattern. ACh promoted single-spike activity whereas atropine promoted high-frequency bursting. The actions of ACh are discussed with reference to recently discovered voltage-sensitive ionic conductances. Because of the modulatory action of ACh on relay cell firing pattern and excitability no firm conclusion can be reached concerning the hypothesis under test here. We tentatively suggest a dual role for ACh as both neurotransmitter and neuromodulator.     

Patterns of spontaneous unitary discharge in thalamic ventro-basal complex during wakefulness and sleep

Summary Influences of the wake-sleep states on spontaneous activity of thalamic ventro-basal neurons have been studied in the chronic cat using the following analyses for cell discharges: mean firing rate, interspike histogram and joint interval histogram (J.I.H.). While slow wave sleep is accompagnied by a characteristic firing pattern it is more difficult to compare spontaneous unit activity during wakefulness (W) and desynchronised sleep (D).A detailed analysis (especially of the J.I.H.) of the same neuron during the three states indicates marked differences between W and D; on the contrary, the intraburst pattern shows definite similarities between D and S. The greatest stability in the firing pattern of a given neuron is found during S on long recording. During D the variability in the firing pattern is mainly due to phasic activity but may also be related to tonic changes.     

Organization of the thalamo-cortical connexions to the frontal lobe in the rhesus monkey

Summary In 25 rhesus monkeys horseradish peroxidase was injected in different parts of the frontal cortex. The retrogradely labelled thalamic neurons formed longitudinal bands, some of which crossed the internal medullary lamina, and extended from one thalamic nucleus into another. On the basis of these findings the frontal cortex was subdivided into seven transverse cortical strips which receive afferents from seven longitudinal bands of thalamic neurons. The most rostral transverse strip receives afferents from the most medial thalamic band which is oriented vertically and extends through the most medial part of the MD into the medial pulvinar. Progressively more caudally located transverse strips receive afferents from progressively more laterally located thalamic bands which in part are situated in the VL and show an increasing tilt towards the horizontal. Moreover, those parts of the various bands which are situated along the dorsal and lateral margin of the thalamus project to the medial portions of the transverse cortical strips, i.e. along the medial margin of the frontal lobe, while the other parts situated ventromedially in the thalamus project to the lateral portions of these strips, i.e. along the lateral margin of the frontal lobe.These data provide an alternative view of the organization of the thalamus and suggest that this structure contains a matrix of longitudinal cell columns which in some cases extend across specific nuclear borders and may represent the basic thalamic building blocks in respect to the thalamo-cortical connexions.