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K J Dormer

Publications and source records attributed to K J Dormer.

At least 37 records · Page 2Linked to original sources
PubMed1986

Fastigial nucleus projections in the midbrain and thalamus in dogs.

Efferent connections to midbrain and thalamus from portions of the cerebellar fastigial nucleus were investigated using autoradiographic techniques. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area which produced maximal increases in blood pressure and heart rate was localized in each dog. A mixture of [3H]leucine and [3H]proline (4:1) was injected into that area and autoradiograms were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. The rostral-caudal extent of injection sites were mapped in the horizontal plane from sequential coronal, thionin-stained sections and "primary" and "secondary" injection zones were defined according to specific criteria. Labeled axons reached the mesencephalon via the contralateral uncinate fasiculus. Ascending fibers assembled in a diffuse contingent at the prerubral level adjacent to the ventrolateral periaqueductal gray. The heaviest projections were contralateral to the injection site, but ipsilateral terminals were observed as well. In the midbrain, axons entered the contralateral and ipsilateral superior colliculus to branch repeatedly and terminate in the deep and intermediate layers. Additional terminals were observed bilaterally in the nuclei of the posterior commissure and pretectal areas at the midbrain-diencephalic junction. In the thalamus, labeled axons formed into three groups which terminated in: the contralateral paraventricular complex and medial dorsal nucleus; the contralateral central medial, paracentral, parafasicular and central lateral nuclei, and the contralateral ventral medial and ventral lateral nuclei. There was a sparse projection to the ipsilateral ventral lateral nucleus. The contralateral projection to the ventral medial and ventral lateral nuclei was marked by dense clusters of label ventral to the internal medullary lamina extending, in the dorsal ventral lateral nucleus, to its rostral pole. Projections to specific somesthetic thalamus or the hypothalamus were not observed. These ascending projections in the canine brain generally conform to those described in other nonprimate mammals. The fastigial nucleus presumably provides information concerning equilibrium and body proprioception to the superior colliculus and to thalamic nuclei including both specific motor relay and "nonspecific" midline and intralaminar nuclei, much the same as reported in the cat. The projection to the ventral medial and ventral lateral thalamic nuclei terminate in areas known to participate in the control of axial and proximal limb muscle activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1986

Fastigial nucleus cardiovascular response and brain stem lesions in the beagle.

Changes in the excitatory cardiovascular response (heart rate, arterial blood pressure, left ventricular pressure, and LV dP/dt as an index of myocardial contractility) resulting from electrical stimulation of the cerebellar fastigial nucleus (FN) were recorded after placement of DC or radio-frequency lesions or after microinjections of kainic acid into brain stem areas that receive FN projections and have been shown to be involved in central cardiovascular control. FN-induced increases in heart rate, blood pressure, and contractility were reduced or abolished by lesions made in the restiform body or the A5 area, which is homologous to the catecholamine-containing region in cats and rats. Lesions in the paramedian reticular nucleus, rostral and caudal to obex, failed to reduce the FN cardiovascular response. Nucleus of the solitary tract lesions augmented the FN pressor response and tachycardia. Kainic acid (1 microliter of 100 mM solution) caused profound depression of heart rate, blood pressure, and contractility and reduced or eliminated the FN-induced cardiovascular response when injected into the A5 area, previously identified by the pressor response following electrical stimulation. We concluded from these observations that a descending fastigiobulbar sympathoexcitatory pathway courses through a previously identified A5 pressor area that is also capable of a depressor response when the cell bodies alone are activated.

Animals↗
PubMed1986

An implantable hearing device: osseointegration of a titanium-magnet temporal bone stimulator.

The use of bone conduction hearing devices has recently entered the realm of implantable prostheses and solid-state electronics, resulting in improved fidelity and applicability for a wider range of patients. One particular device, a temporal bone stimulator (TBS), consists of an external sound processor and implanted portion to cause vibration under the skin. An implantable temporal bone stimulator screw constructed of titanium alloy with a permanent magnet can be vibrated by inductive transcutaneous coupling. The safety and osseointegration of the TBS bone screw were tested in adult goats that were free-field stimulated at 75 dB with the TBS processor for 4 to 21 weeks. Histologic comparisons of the soft tissue and bone adjacent to active and passive screws revealed no remarkable differences between them with bone growing in the interstices of the threaded portion. Evidence for mild reorganization of bone was shown with Goldner's stain, which differentiated bone that was young and unmineralized from bone that was older and mineralized. Reorganization was evident in both the active and passive sites and there was no remarkable difference between the two in a blind study. Additional evidence for the integrity of the implant was obtained by subjecting a calvarium containing both screws to a 5000 gauss magnetic field for 10 minutes of a nuclear magnetic resonance head scan. The calvarium was first dissected free from overlying skin and connective tissue. The magnet-containing screws were not loosened. We conclude that the implanted screw portion of the TBS implantable hearing device is well-integrated into the temporal bone. Mild stimulation of new bone growth indicates a healthy long-term viable implant for bone conduction amplification of sound.

Animals↗
PubMed1985

Neural regulation of the cardiovascular system during exercise.

Neural components important in control of the cardiovascular system during exercise can be divided into central nervous system (CNS) components and peripheral components. CNS components would include the cerebral cortex, cerebellum, medullary region of the brain stem, and the spinal cord. Peripheral components would include the efferent limbs of the autonomic nervous system and afferent fibers carrying information to the CNS. The neural pathways involved in the control of cardiovascular system during exercise and the relationship between the various neural components have been actively pursued in the last few years. Several new studies suggest that information arising from the active muscles and the cardiovascular system itself may be important in the control of the cardiovascular system during exercise. The cerebellum may play a modulating role in the cardiovascular response. The information from the peripheral afferent fibers, the cerebellum, and the cerebral cortex is integrated in the brain to result in overall neural control. Exercise training probably modifies the central integration of information and modifies the cardiovascular response to exercise and other stresses.

Afferent Pathways↗
PubMed1984

Fastigial nucleus projections to the brain stem in beagles: pathways for autonomic regulation.

Efferent connections from a portion of the cerebellar fastigial nucleus were investigated using autoradiography. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area that produced increases in blood pressure and heart rate was localized. A mixture of [3H]leucine and [3H]proline (4:1) was injected into the area and autoradiograms of transported material were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. Labeled axons reached the brain stem via two routes, the ipsilateral juxtarestiform body and the contralateral uncinate fasciculus. Ventral portions of the lateral vestibular nucleus were labeled bilaterally, projections to the inferior vestibular and medial vestibular nuclei are contralateral. Nucleus tractus solitarius was heavily labeled on the side opposite the injection. The contralateral medial reticular formation contained many labeled terminals and axons. Label was found in the nucleus reticularis ventralis, lateral reticular nucleus, nucleus gigantocellularis, nucleus pontis caudalis and the paramedian reticular nucleus. No terminal labeling was found in nucleus parvocellularis or nucleus ambiguous. Stimulation of the rostral fastigial nucleus produces increases in blood pressure and heart rate by generalized sympathoexcitation. Many cell groups which facilitate the activity of preganglionic sympathetic neurons do not receive direct fastigial input. It is suggested that that sympathoexcitation resulting from stimulation of the fastigial nucleus occurs through multisynaptic connections in the brain stem.

Animals↗
PubMed1984

Modulation of cardiovascular response to dynamic exercise by fastigial nucleus.

Mongrel dogs (n = 34) were used to record the cardiovascular responses during submaximal exercise-tolerance tests (ETT) before and after the placement of lesions in rostral portions of the cerebellar fastigial nucleus (FN). Sterile surgical procedures were used to implant solid-state pressure transducers into the left ventricle or descending aorta (anesthesia 1% halothane in O2) and multipolar stainless steel electrodes into FN (anesthesia alpha-chloralose 115 mg/kg iv). Heart rate (HR), maximal left ventricular systolic pressure ( LVPmax ) and its first derivative ( dLVP /dt), and mean arterial blood pressure (MAP) were recorded during a motorized treadmill ETT. Electrolytic direct-current or radio-frequency lesions were made through the indwelling FN electrodes, and the ETT was repeated following 10-14 days recovery. Two-way analysis of variance (ANOVA), with repeated measures on one, and one-way ANOVA for simple effects indicated a significant reduction in HR and MAP (P less than 0.01) but not LVPmax and dLVP /dt occurred during exercise as a result of rostral FN lesions. Although the trend for reduced LVPmax and dLVP /dt was also evident, a relatively greater decrease in blood pressure occurred in the peripheral vasculature during exercise. It was concluded that FN acts as a modulator of HR and MAP during dynamic exercise because of the observed deficits, and because FN is known to both send efferent projections to medullary vasomotor areas and receive projections from motor cortex and muscle and joint afferents.

Afferent Pathways↗
PubMed1983

Bilateral lesions of the fastigial nucleus prevent the recovery of blood pressure following hypotension induced by hemorrhage or administration of endotoxin.

The present studies were undertaken to determine if bilateral lesions of the fastigial nuclei of the cerebellum would impair the recovery and maintenance of mean arterial blood pressure during hypotension caused by hemorrhage or administration of endotoxin. We had shown previously that cerebellectomy would produce such an impairment, and the fastigial nuclei were implicated as the specific area involved due to the known pressor response observed when they are stimulated electrically. Chloralose-anesthetized dogs were made hypotensive by administration of E. coli endotoxin or hemorrhage to 50 mm Hg and observed over the subsequent 3 h. Dogs with fastigial nucleus lesions had a significantly lower mean arterial pressure during both the recovery and maintenance phases when compared with intact animals under both hypotensive protocols. In the hemorrhage study, a significant number of lesioned animals died whereas none of the controls died. Lesion of the fastigial nuclei produced an impairment similar to that seen with cerebellectomy. It is concluded that the fastigial nuclei play an important role in the recovery of blood pressure following a hypotensive episode.

Animals↗
PubMed1982

Fastigial nucleus stimulation and excitatory spinal sympathetic activity in dog.

To locate the cerebellar-activated descending sympathetic pathways in the dog the fastigial nucleus (FN) was electrically stimulated in chloralose-anesthetized dogs while recording from sympathetic preganglionic neurons. Physiological interventions included lesions in the dorsolateral funiculus (DLF) of the spinal cord, myelotomy, arterial pressure changes, bilateral occlusion of the carotid arteries, and administration of clonidine. Multiunit activity at the T2 on T3 white ramus communicans was recorded on-line during rest and FN stimulation. Descending sympathetic activity (averaging 3.5 m/s) in the DLF was increased in response to FN stimulation but was significantly reduced by ipsilateral and eliminated by bilateral FN lesions. When testing for the effects of baroreceptor reflexes on the sympathetic pathway phenylephrine-induced hypertension decreased, but moderate hemorrhage increased the amount of preganglionic activity at rest and during FN stimulation. During hypertension and simultaneous carotid artery occlusion the amount of sympathetic activity that could be evoked was comparable to that evoked during normotensive states. Clonidine (IV) reduced the FN sympathoexcitation, but direct stimulation of the DLF indicated that clonidine had sympathoinhibitory activity at both medullary and spinal sites. In summary, rostral FN primarily excited ipsilateral descending sympathetic pathways in DLF, and this sympathoexcitation was partially inhibited by baroreceptor intervention.

Animals↗
PubMed1981

The use of rare-earth magnet couplers in cochlear implants.

The cochlear implant is an electronic auditory prosthesis gaining widespread acceptance as a means of restoring partial hearing to the totally deaf. A number of engineering and biological hurdles remain toward the improvement of existing implantable systems and development of multichannel systems. One hurdle concerns reliable transcutaneous coupling of the external electric signal to the implanted device. To date this has been accomplished by inductive means through coils which were mechanically held in place. The incorporation of small, permanent, rare-earth (SmCo5) magnets with the coil assemblies has eliminated the unreliable mechanical supporting devices. Magnetic attachment was simulated in dogs to examine for biological compatibility. Electron micrographs indicated normal subcellular structures in tissue exposed for 10 weeks. Five patients were implanted with magnet-modified coil assemblies and tested for the proper alignment and support of the external coil assembly, as well as efficiency of inductive coupling. Electromagnetic coupling was not interfered with and mechanical support was adequate. We conclude that rare-earth magnets provide an effective means for supporting and positioning in place medical devices, such as the cochlear implant.

Animals↗
PubMed1980

Interaction of fastigial pressure response and depressor response to nasal perfusion.

The fastigial nucleus pressor response (FPR) and the nasal-perfusion diving response were elicited alone and simultaneously to observe the net effect on cardiovascular variables. The fastigial nucleus was electrically stimulated in 14-chloralose-urethane anesthetized dogs and the FPR was characterized by a transient tachycardia with sustained elevations in arterial pressure, left ventricular pressure and maximal dP/dt. The tachycardia was buffered by baroreceptor reflexes during the elevated arterial pressure of the FPR. All variable of the FPR, however, were reduced by superimposition of the diving response upon the FPR. Heart rate was most sensitive to depression by the nasal perfusion which elicited a bradycardia as much as 70 beats/min below the control rate. The nasal-evoked diving response was discussed with respect to the trigeminal depressor response which results from direct stimulation of the spinal trigeminal complex. Algebraic cancellation of the FPR and dive responses is considered along with anatomical and electrophysiological evidence which suggests that these two responses, as well as the baroreceptor reflex, could be integrated at a common site. This site may be the medullary nucleus of the solitary tract which receives projections from trigeminal and glossopharyngeal nerves and from the fastigial nucleus.

Adrenergic Fibers↗
PubMed1980

Neural control of the heart during arrhythmias and exercise.

Involvement of neural activity during cardiovascular adjustments and during arrhythmias can be determined by comparing the results of cardiovascular changes after lesions are made in nuclei or pathways of the central nervous system or ablations of ganglia or nerves are made in the peripheral nervous system. The neural effects can be exaggerated if these systems are forced to perform at higher levels during a stressful situation. The purpose of this presentation is to discuss the responsiveness of the cardiovascular system after left or right stellate ganglionectomy and after lesions are made in the fastigial nucleus of the cerebellum in dogs stressed with submaximal exercise. These dogs are implanted with instruments that are designed to measure cardiovascular responses. Hypotheses for potential neural mechanisms are generated from the results of chronic animal studies, and these mechanisms are tested in anesthetized dogs and cats. Electrical stimulation of ascending and descending pathways in the central nervous system and stimulations such as coronary occlusion and mechanical probing are used to activate neural mechanisms in the anesthetized state. A general schema concerning the results of our studies provides further information about our approach to understanding the physiological role that the central nervous system may exert on the cardiovascular system during stress.

Afferent Pathways↗
PubMed1976

Cerebellar pressor response in the dog.

A fastigial pressor response has been elicited in the anesthetized mongrel dog. Stimulation within the rostral portions of this nucleus results in mean arterial pressure rises up to 150 mmHg above control. A proportional tachycardia is simultaneously evoked which may rapidly attain heart rates of 190 beats/min above control levels. Peak tachycardias immediately suside and often the heart rate declines below control values during stimulation while arterial pressure remains elevated. When either the carotid sinuses were isolated by ligation or a bilateral vagotomy was performed, the fastigial tachycardia was sustained. Thresholds for the response are near 0.05 mA and the stimulus intensity curve is linear to 0.4 mA whereupon the pressure rise and tachycardia begin to approach a plateau value. The response could still be attained when submaximal doses of alpha-chloralose anesthesia or high levels of barbiturates (30-40 mg/kg) were given. Both portions of the response result from widespread sympathetic activation; however, buffering of the response through the baroreceptor reflexes is only demonstrated in the cardiac segment of the response.

Animals↗