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F W Kerr

Publications and source records attributed to F W Kerr.

14 recordsLinked to original sources
PubMed1979

Organization of trigeminothalamic tracts and other thalamic afferent systems of the brainstem in the rat: presence of gelatinosa neurons with thalamic connections.

Thalamic projections from trigeminal and certain other nuclei of the brainstem of the rat have been investigated using the technique of retrograde transport of horseradish peroxidase (HRP). The pattern of trigeminothalamic projections is very specifically related to the individual subnuclei of the complex. The Main Sensory Nucleus (MSN) provides profuse cross connections to the ventrobasal thalamus (VB); these arise exclusively from medium and small-sized neurons, but never from the large cells. In addition to these crossed connections, a small ipsilateral dorsal trigeminothalamic tract arises from the dorsal third of the most rostral part of the MSN; this is the only ipsilateral connection to VB found in the trigeminal complex. Subnucleus Oralis has no projections to the thalamus; it is suggested that it may be concerned primarily with reflex activation of the facial nucleus, with which it is co-extensive in the rostro-caudal axis. Subnucleus Interpolaris has a well-defined crossed projection of moderate size which arises from the large, medium and some of the small neurons. Subnucleus Caudalis has a sparse output to the thalamus and differs in its projections from rostral to caudal. At the most rostral level, all layers (marginal, transitional gelatinosa and magnocellularis) contain neurons which project to the thalamus; particularly conspicuous in this respect are the marginal neurons, most of which are strongly labelled. The presence of gelatinosa neurons projecting to the thalamus emphasizes a point made in earlier reports, that these neurons do not form an homogeneous population. At caudal levels, the marginal neurons are the major source of thalamic projections, while connections to the thalamus form deeper lying neurons are infrequent. With a single exception, the medullary reticular nuclei contained no neurons with thalamic connections; a small number of reticulo-thalamic neurons were found in the ventral pontine area. Marked labelling of the medial cuneate nucleus and moderate labelling of the gracilis and lateral cuneate nuclei occurred contralaterally to the injection site. A small numebr of medial cuneate and gracile neurons project to the ipsilateral thalamus. Projections from the solitary nucleus were always ipsialteral. The boundaries of individual subnuclei of the lateral sensory trigeminal complex in the rat have been redefined on the basis of cytological criteria; these are in good accord with the corresponding thalamic projection patterns.

Animals↗
PubMed1978

Pain.

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Afferent Pathways↗
PubMed1978

Pain.

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Animals↗
PubMed1975

Neuroplasticity of primary afferents in the neo-natal cat and some results of early deafferentation of the trigeminal spinal nucleus.

The plasticity of cervical primary afferents has been investigated in young adult cats in which the trigeminal root, together with most of the ganglion, had been excised via a new approach to these structures during the first week after birth. Once degeneration debris had disappeared, bilateral ganglionectomies of the upper three cervical dorsal roots were done in five animals and the IXth and Xth roots transected on the side of the chronic trigeminal denervation in one instance; the degeneration pattern on the chronically denervated side was compared to that on the normal side. There was mild evidence of increased degeneration of the cervical afferents in the C1 segment and in the medulla (subnucleus interpolaris of V) on the chronically denervated side. The proliferation was more apparent in the kitten operated at three days of age and was only vestigial in animals operated at six or seven days; it had no appreciable tendency to extend into the large contiguous pool of denervated trigeminal neurons. There was no evidence of sprouting of the IXth and Xth nerve afferents. These observations indicate that primary afferents of the upper cervical roots and of the glossopharyngeal and vagus nerves have little neuroplastic potential even at early stages. The literature on neuroplasticity is controversial and a brief review of this together with suggestions regarding the reasons for some of these conflicts is presented. Some structural and functional effects of chronic trigeminal denervation are briefly described.

Animals↗
PubMed1975

The ascending projections of the dorsolateral funiculus of the spinal cord in the primate.

The ascending projections of the dorsolateral funiculus of the spinal cord to the brain stem have been determined in five macaque monkeys. Connections to the lateral cervical nucleus and to the reticular nucleus of the cord in the C1 and C2 segments are present. In the medulla the most prominent connections are to the nuclei "Z" and "x" of Brodal and Pompeiano, to the rostral portion of n. gracilis and to the n. proprius of the restiform body. Minor projections reach the rostral part of the medial and lateral cuneate nuclei, the reticular nucleus, the n. centralis dorsalis and the periependymal gray. There were no projections to planes rostral to the medulla. In view of the connections established it is concluded that ascending systems in the DLF to the brain stem of primates are concerned with transmission of mechanoreceptor input to the cerebellum and thalamus and that nociceptive relay appears very unlikely.

Animals↗
PubMed1975

The ventral spinothalamic tract and other ascending systems of the ventral funiculus of the spinal cord.

The ascending degeneration resulting from experimental lesions of the ventral funiculus of the spinal cord of Macaca mulatta has been studied using the Nauta technique and its variants. The ventral spinothalamic tract is shown to be an independent entity with respect to the lateral spinothalamic tract; its fibers are widely distributed in the ventral funiculus and it establishes connections with the brain stem and thalamus which are analogous but not identical to those of the latter. Its role in the relay of nociceptive input is discussed in view of the similarity in hodology of the two systems and it is proposed that it may be responsible for the failure of anterolateral cordotomy to control pain on a long term basis. Other ascending systems in the ventral funiculus include the spino-olivary and spino-reticular tracts, as well as minor connections to the N. of Edinger-Westphal, the red nucleus and the superior colliculus. The projections from the ventral quadrant of the spinal cord to the brain stem are almost entirely ipsilateral until the rostral mesencephalon is reached, at which level the N. of Darkschewitz receives both ipsilateral and crossed input; the magnocellular nucleus of the medial geniculate body receives a small contribution which is mainly ipsilateral. In the thalamus the VPL receives predominantly ipsilateral projections while the input to the paralaminar nuclei is only slightly less pronounced contralaterally than ipsilaterally.

Animals↗
PubMed1975

Vasodilator system for the face.

The authors describe investigations in cats to delineate a vasodilator system to the face, which they undertook after a previous study showed that radiofrequency coagulation of the trigeminal ganglion produced a pronounced flush in the skin of the corresponding division. Results demonstrate a vasodilator system emerging from the brain stem with the facial nerve which, by way of the greater superficial petrosal nerve, reaches the trigeminal ganglion. There the fibers are distributed to each of the divisions of the fifth nerve; in addition, a moderate number of vasodilator fibers also appear to leave the brain stem directly with the trigeminal nerve. Vasodilator fibers also appear to leave the brain stem directly with the trigeminal nerve. Vasodilator effects were elicited by stereotaxic stimulation of the facial and trigeminal nuclei in the brain stem. There is, therefore, a dual vasomotor control of the facial cutaneous vascular bed; the classical sympathetic vasoconstrictor system of the face is complemented by a vasodilator system capable of producing changes of equal but opposite amplitude in vessel caliber.

Animals↗
PubMed1975

Microcirculatory obstruction in focal cerebral ischemia. Relationship to neuronal alterations.

The cerbral microcirculation in squirrel monkeys was studied by the carbon perfusion technique after middle cerebral artery occlusion. No filling impairment was detected with 90 minutes of ischemia, and only slight impairment was detected with 3 hours of ischemia. Severe microcirculatory obstruction was found after ischemia longer than 3 hours. The obstruction appeared to be at the capillary level and seemed partly the result of narrowing of cappillary channels by perivascular glial swelling and developing cerebral edema. The relationship between the developing microcirculatory obstruction and the distribution and severity of the neuronal alterations was studied. The results of this investigation using the same experimental model suggest that obstruction of parenchymal vessels does not play a major role in the production of an infarct in areas of acute focal ischemia.

Animals↗
PubMed1975

Pain. A central inhibitory balance theory.

Knowledge of the segmental neuronal circuitry for noxious and non-noxious input is a necessary prelude to understanding pain mechanisms. Significant gaps in our understanding of the synaptology of these pathways in the dorsal horn have hindered progress in this area. This report describes the excitatory and inhibitory circuits that supply the marginal neurons of the spinal cord, whose role in nociceptive mechanisms is well established. On the basis of these data, it is proposed that large primary afferents (non-noxious) provide heavy inhibitory input to marginal neurons via gelatinosa cells. Conversely, small primary afferents (nociceptive) provide excitatory input to marginal neurons but relatively little inhibitory feedback to these cells via gelatinosa neurons. The modulation of pain-producing input depends thus on the balance between large-fiber and small-fiber activity via a postsynaptic inhibitory mechanism acting on the nociceptive relay neurons. This theory accounts satisfactorily for the modulation of pain by counterirritation and by various methods of stimulating large-fiber input.

Animals↗