Dual morphology and topography of the corticothalamic terminals originating from the primary, supplementary motor, and dorsal premotor cortical areas in macaque monkeys.

In the motor, somatosensory, and auditory systems of rodents and cats, the corticothalamic connection is composed of a main projection formed by small endings and a minor projection terminating with giant endings. To establish whether the corticothalamic projection originating from motor cortical areas in primates exhibits the same duality, the anterograde tracer biotinylated dextran amine was injected in eight macaque monkeys in the primary motor (M1; n = 3), the supplementary motor (SMA; n = 3) and the dorsal premotor (PMd; n = 2) cortical areas to label corticothalamic axons. The corticothalamic projection originating from these three motor cortical areas was characterized by the presence of axon terminals constituting the same two types of endings, observed both as boutons en passant and terminaux. The population of small endings exhibited a mean cross-sectional maximum diameter of 0.95 microm (S.D. = 0.23), a range of diameters not overlapping that of giant endings (mean diameter = 3.46 microm, S.D. = 0.74 microm). Topographically, the giant endings originating from M1 were located in the same thalamic nucleus (ventroposterolateral nucleus, oral part) in which the small endings were found. In contrast, the giant endings originating from SMA and PMd were located in a thalamic nucleus (mediodorsal nucleus) distinct from the main termination zone formed by small endings. Along the rostrocaudal axis, the giant endings were distributed in a restricted zone, irrespective of the origin of the projection (M1, SMA, PMd). The dual morphology of corticothalamic endings, previously found in rodents and cats, is present in the motor system of subhuman primates for both primary and nonprimary motor cortical areas.

The hypothalamocerebellar projection in the cat: branching and nuclear termination.

The hypothalamic projection to the cerebellar nuclei and cortex in the cat was studied by means of retrograde transport of wheat germ agglutinin-horseradish peroxidase complex and various fluorescent tracers. The hypothalamocerebellar nuclear projection originates from various parts of the posterior hypothalamus and reaches mainly the ipsilateral fastigial and interposed nuclei, but all nuclei receive some hypothalamocerebellar fibres. It appears from our double labelling experiments that at least one half of the hypothalamocerebellar nuclear neurones by means of axon collaterals also projects to the cerebellar cortex. Experiments with depositions of fluorescent tracers in both cerebellar hemispheres show that some hypothalamocerebellar fibres branch to reach different parts of the cerebellar cortex. Previous studies have shown that hypothalamocerebellar axons may be branches of hypothalamic efferents to other sites. However, experiments with combined fluorescent tracer depositions in the cerebellum and hippocampus gave no evidence for hypothalamic neurones with axon collaterals to both these regions.

Morphological data concerning the acupuncture points and channel network.

Through its traditional rules, the practice of acupuncture requires knowledge of the channel networks and point locations. For nearly three centuries, morphological research did not show any evidence on peripheral morphological support of the channels. Their courses appear as referred sensations, and the persistence of propogated sensations along the channels in amputees and their cessation after total section of the spinal cord implicates a neuraxial participation. The spatial sequence of the segmental centers seems to be the indispensable primary structure. Through the various centers having a topical organization, the somesthetic areas appear as the necessary structural support of the propogated sensation along the channel. Acupuncture points are less discussed as a basis of acupuncture in the West, but they do have equivalences in all medical systems. Nervous structures are necessary for acupuncture to work, and complete denervation totally suppresses the effect of the points. There is not only one type of acupuncture point but many of them, and the concomitant stimulation of multiple and clearly defined structures is necessary to obtain the acupuncture sensation, De Qi. Thus, the effect seems strictly correlated with convergence of nerve impulses on the primary centers. Lastly, accurate anatomical knowledge of the point and its correct puncture (location, direction, depth) are indispensable to get satisfactory therapeutical effects and to avoid iatrogenic incidents.

The location of LH-RH neurons in the rat hypothalamus and their pathways to the median eminence. Experimental immunohistochemistry and radioimmunoassay.

The location of the perikarya of LH-RH neurons in the rat hypothalamus and their pathways to the median eminence were studied by immunohistochemistry and radioimmunoassay after placing stereotaxic electrolytic lesions in several parts of the hypothalamus. The principal location of the cell somata was found to be in the ventral part of the medial preoptic area; their pathways were classified into a main baso-lateral pathway and an accessory descending pathway branching off from the former. The main pathway was found to cross in the vicinity of the corresponding neuronal perikarya. The central median eminence and the dorsal and ventral walls of the tubero-infundibular sulcus of the caudal part of the median eminence are innervated mainly by the baso-lateral pathway. On the other hand, the rostral and most caudal protions of the median eminence are innervated principally by the descending pathway and have a subsidiary dual innervation. The projection of LH-RH neurons to the OVLT is believed to originate from perikarya adjacent to this circumventricular organ.

Histological and electrophysiological investigation of lizard skeletal muscle.

1. The patterns of innervation and electrical properties of muscle fibres in a skeletal muscle of the blue tongue lizard Tiliqua nigrolutea have been investigated.2. Gold impregnation of nerve terminals and staining of muscle fibre junctional areas for cholinesterase showed that there are two histological types of muscle fibre in scalenus muscles of the lizard: (a) those usually receiving single en plaque innervation, and (b) those that receive multiple en grappe terminations.3. In normal solution and in solutions to which small doses of curare were added, two types of subthreshold post-junctional response were recorded following nerve stimulation, (a) potentials with rapid rates of rise and a half-decay time of less than 10 msec and (b) responses with fast rise times and long half-decay times (50 msec or more).4. Fast time course subthreshold responses often gave rise to propagated action potentials. In curarized preparations ((+)-tubocurarine 0.4-1.0 mug/ml.) action potentials failed, giving way to junction potentials of decreasing amplitude, when stimulation was maintained at rates of 5/sec or more. The decay phases of fast time course potentials were closely approximated by error functions.5. Slow time course responses summated during repetitive stimulation, but action potentials were never produced. The decays of slow junction potentials were well fitted by exponentials. It is suggested that fibres in which they were recorded received distributed, en grappe innervation.6. Fibres in which fast time course junction potentials were recorded were excited by direct stimulation via an intracellular micro-electrode. They had apparent membrane resistance and capacity of about 4000 Omega. cm(2) and 7 muF/cm(2).7. Fibres exhibiting slow junction potentials could not be excited directly, even when depolarizing pulses were preceded by hyperpolarizations of 50 mV or more for more than 20 msec. Such fibres had an apparent membrane resistance of 31 x 10(3) Omega.cm(2) (mean) and a capacity of less than 3 muF/cm(2) (eight fibres).8. Curarized muscles developed tension in response to nerve stimulation at frequencies of 5/sec or more. The tension profile was smooth at even the lowest frequencies at which a response was elicited. Normal fusion frequency was around 50/sec.9. It is suggested that fibres exhibiting slow junction potentials were functionally similar to amphibian tonic fibres.10. Some fibres were found in which action potentials could be elicited by stimulation of one or more axons. Their subthreshold responses and passive properties were not determined and it remains uncertain to which of the two structural types they belong.