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Biomedical subjects

B Ghelarducci

Publications and source records attributed to B Ghelarducci.

At least 37 records · Page 2Linked to original sources
PubMed1990

An electrophysiological and anatomical study of afferents reaching the cerebellar uvula in the rabbit.

Stimulation of a medial region of the cerebellar uvula cortex produces sympathetically mediated cardiovascular effects in the decerebrate rabbit. In the present study the afferents to this cerebellar area have been determined using electrophysiological and neuroanatomical methods. Field potentials of prevalent mossy origin evoked by single-shock stimulation of different peripheral nerves have been recorded from sublobules IXa and IXb. No response to vagus and aortic nerves stimulation has been found. A modulation of Purkinje cell discharge following natural vestibular stimulation has been found. A modulation of Purkinje cell discharge following natural vestibular stimulation has been recorded from sublobules IXb and IXc. The retrograde transport of horseradish peroxidase from the uvula cortex has revealed a widespread afferent input to this cerebellar region arising from brain stem reticular and sensory nuclei. On the basis of the results obtained, together with the results of experiments performed in conscious rabbits, contained in the following paper (Bradley, Ghelarducci, La Noce & Spyer, 1990), it is suggested that the uvula participates in co-ordination of the visceral and somatic components of the alerting reaction in the rabbit.

Afferent Pathways↗
PubMed1990

Autonomic and somatic responses evoked by stimulation of the cerebellar uvula in the conscious rabbit.

The present study has investigated the effects of electrical stimulation of the cerebellar posterior cortex in the conscious rabbit. Stimulation of lobule IX (the uvula) elicited an increase in mean arterial blood pressure and heart rate, accompanied by EEG desynchronization, pupillary dilatation and a specific motor reaction, consisting of pricking of the ears, neck stiffening and running movements. Stimulation of lobule VIII was ineffective in evoking equivalent responses. The administration of barbiturates reversed the cardiovascular response to uvula stimulation, producing a fall in mean arterial pressure. The characteristics of the pattern of responses obtained, together with the anatomical and electrophysical observations provided in the preceding paper (Bradley, Ghelarducci, La Noce, Paton, Spyer & Withington-Wray, 1990), suggest a possible involvement of uvula cortex in the expression of the alerting reaction in the rabbit.

Analysis of Variance↗
PubMed1988

Dark-rearing modifies serotonin and 5-hydroxyindoleacetic acid contents in specific regions of rabbit brain.

The contents of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in specific brain regions of rabbits dark-reared from birth until 3 months of age are higher than those of controls. After light exposure, 5-HT and 5-HIAA levels become similar to normal values. In adult rabbits kept in darkness for 3 months, 5-HT and 5-HIAA contents increase only in the superior colliculi. These results are discussed in relation to the early development of the vestibulo-ocular reflex.

Afferent Pathways↗
PubMed1987

The cardiovascular responses elicited from the posterior cerebellar cortex in the anaesthetized and decerebrate rabbit.

1. In this study the posterior cerebellar cortex has been electrically stimulated and changes in heart rate, arterial blood pressure, regional blood flows and renal sympathetic nerve discharge have been recorded in both the anaesthetized and the decerebrate unanaesthetized rabbit. 2. Specifically, lobules VII, VIII, IX and X of the posterior cerebellar vermis were stimulated but the only region which elicited cardiovascular changes was lobule IX (the uvula). The responsive area of the uvula was localized to the medial regions of sublobules a, b and c and was identical in both anaesthetized and decerebrate animals. 3. Under urethane anaesthesia, uvula stimulation evoked a small bradycardia, a fall in arterial pressure, a transient inhibition of renal sympathetic nerve activity, with no change in renal vascular conductance, and an increase in femoral vascular conductance. 4. Stimulation of an identical area in the decerebrate rabbit evoked a marked tachycardia, an increase in blood pressure, maintained increase in renal sympathetic nerve discharge, and decreases in both renal and femoral conductances. 5. The response evoked from the decerebrate rabbit could be reversed by a small dose of anaesthetic to a pattern of response which was essentially identical to that seen in the urethane-anaesthetized rabbit. 6. This influence of anaesthetics on the pattern of cardiovascular responses that may be elicited from the cerebellar cortex indicates that caution should be exercised when making physiological inferences on the basis of stimulation experiments in anaesthetized preparations. 7. In the light of the cardiovascular changes that may be evoked from the uvula, and recent neuroanatomical and neurophysiological data concerning afferent and efferent connexions of this cerebellar region, we discuss the possibility that the uvula plays a role in the alerting reaction of the rabbit.

Anesthesia, General↗
PubMed1984

Development of vertical vestibulo-ocular reflex characteristics in intact and flocculectomized rabbits visually deprived from birth.

The vertical vestibulo-ocular reflex (VOR) was recorded in dark-reared rabbits 3 months of age submitted in the dark to lateral sinusoidal oscillations of different frequencies and fixed amplitude. While the phase of the response was perfectly adequate to ensure head movements compensation, the gain values recorded showed a clear reduction with respect to the values obtained in a normally raised control group of the same age. After exposure to light, the visually deprived animals showed a complete and rapid recovery of normal VOR gain values. Another group of animals was flocculectomized prior to light exposure. The bilateral ablation of flocculus and paraflocculus did not affect the VOR characteristics of the deprived animals. After exposure to light, in the flocculectomized animals, no recovery of the VOR gain values was observed. The present results confirm that visual experience in early life is necessary for a correct development of the VOR. If visual deprivation is limited to the first few months of life, the impairment of the reflex characteristics is completely reversible. Finally our data suggest that in the rabbit, the flocculus controls the early life development of the VOR.

Animals↗
PubMed1984

Development of the dynamic characteristics of the horizontal vestibulo-ocular reflex in infancy.

The horizontal vestibulo-ocular reflex (VOR) has been recorded electrooculographically in normal infants aged from one to four weeks and in older subjects submitted to sinusoidal oscillations (+/- 15 degrees, 0.05-0.5 Hz) in the dark. The analysis of the dynamic characteristics of the reflex indicates that, at least in the low frequency range, the VOR has not yet attained a truly compensatory role in the first month of life. In two of the subjects the VOR has been followed throughout the second month of life. At this age the phase of the reflex has already developed the characteristics of the comparison-group at all the frequencies of stimulation, while the trend of the amplitude modulation has not yet changed from the newborn stage. By the 6th month of life the VOR characteristics are comparable with those present in the comparison-group. It appears therefore that the horizontal VOR undergoes a process of maturation during the early period of life, which affects in different times both phase and amplitude values. The possible role exerted by different neural structures on this maturation process is discussed.

Female↗
PubMed1984

Recovery of the vertical vestibulo-ocular reflex gain in rabbits submitted to bilateral and unilateral visual deprivation from birth.

Rabbits were raised in complete darkness from birth to the age of 3 months. At this age, the animals were submitted to dynamic vestibular stimulation consisting of lateral sinusoidal oscillations of different frequencies and fixed amplitude. The vertical VOR, elicited in complete darkness, was then recorded. While the phase of the response was perfectly adequate to ensure head movements compensation, the gain values recorded were clearly reduced with respect to the values obtained in a normally raised control group of the same age. After exposure to light, the visually deprived animals showed a complete recovery of normal VOR gain values in a relatively short period of time. Another group of animals was submitted to monocular prolongation of light deprivation during the fourth month of life. After 2 weeks these rabbits displayed a clear unbalance of the VOR between the two eyes: the eye in which vision was allowed showed a complete recovery of VOR gain values, while the gain of the occluded eye remained unchanged. The present results confirm that visual experience in early life is necessary for a correct development of the VOR. If visual deprivation is limited to the first few months of life, the impairment of the reflex characteristics is completely reversible. Finally, data on monocular deprivation suggest that, in the rabbit, the neural structures which preside to the development of the vertical VOR compensatory properties are lateralized.

Animals↗
PubMed1983

EMG responses of the vertical eye muscles to dynamic and static natural vestibular stimulation about different axes in alert rabbits.

The EMG responses of the vertical eye muscles have been recorded in alert intact rabbits submitted to both dynamic and static natural vestibular stimulations about different axes. Following dynamic vestibular stimulation, the phase lead of the EMG response with respect to head position as well as its sensitivity increased with stimulus frequency in all the stimulation modalities. This indicates a progressive recruitment by the stimulus of the second-order vestibular neurons related to semicircular canals. The sensitivity of the response was consistently higher in the effective intermediate roll-pitch modality for all the 4 muscles. Following static stimulation, the EMG response showed an asymmetric modulation. The excitatory response was always higher than the inhibitory one and linearly related with the stimulus. Also for the static stimulation the amplitude of the response was significantly higher when the animal was tilted about the effective intermediate roll-pitch axis for all the 4 muscles. The presence of a maximal EMG response in the same modality for both static and dynamic stimulation indicates a similar spatial organization of those subgroups of ampullar and macular receptors projecting to the same eye muscle.

Acoustic Stimulation↗
PubMed1982

Vestibular mechanisms related to vertical and torsional eye movements.

1. A series of experiments concerning the organization of the vertical vestibuloocular reflex (VOR) of the rabbit are reviewed. 2. Unanesthetized, encéphale isolé and intact, alert rabbits have been submitted to natural stimulation of the labyrinth consisting in sinusoidal oscillations and static tilts around the longitudinal axis. The oculomotor responses have been recorded at the level of the III nucleus oculomotor neurons (OMN) and from the four vertical eye muscles. 3. The phase and gain of the OMN response at different frequencies of oscillation indicate a serial involvement of the macular ampullar labyrinthine receptors in the activation of the OMN. In the low frequency range of head movements, macular receptors alone can provide adequate ocular compensation. By raising the frequency of head movements, the threshold value of acceleration for recruiting second order vestibular neurons related to semicircular canals is reached and the vertical VOR is controlled predominantly by the ampullar receptors of the vertical canals. 4. These results have been confirmed and extended in the alert, intact rabbit. By orienting the animal in different positions with respect to the axis of oscillation it has been possible to activate selectively one or the other pair of complementary vertical canals. The EMG responses recorded from the vertical eye muscle exhibited different magnitudes in the different orientations, while the phase curve remained the same. 5. The static otolith-ocular reflex has also been investigated by tilting the alert animals oriented in the same way. The pattern of the EMG responses elicited by the pure macular input coincides with that obtained during dynamic stimulation. The existence of separate functional macular regions specifically connected with the different eye muscles and a close convergent action of the two types of labyrinthine receptors in ocular compensation, are suggested.

Animals↗
PubMed1981

Phase changes induced by ketamine in the vertical vestibulo-ocular reflex in the rabbit.

The effect of ketamine has been tested on the phase of the vertical vestibulo-ocular reflex of rabbits sinusoidally oscillated at various frequencies. A significant phase lag, predominantly affecting the macular component of the reflex, was observed. This action resembles that induced by Nembutal in the same preparation. A specific action of ketamine on synaptic transmission is suggested. Erroneous phase relationship between natural stimuli responses can be obtained in experiments employing ketamine.

Animals↗
PubMed1980

Vestibular inputs to the fastigial nucleus; evidence of convergence of macular and ampullar inputs.

1. Experiments have been undertaken on 11 decerebrate cats to investigate the effects of natural vestibular stimulation on the activity of cerebellar fastigial neurons. 2. From recordings in the rostral portion of the nucleus during sinusoidal lateral (roll) and horizontal (yaw) rotation, distinctive patterns of response were observed. 3. The majority of neurons sensitive to vestibular stimulation showed responses to a single modality of vestibular activation. During lateral tilt some neurones showed positional sensititivy, others gave responses related tothe velocity of movement. Other neurones responded in phase with the velocity of movement in the horizontal plane. 4. Aside from these neuronal responses, others provided indications of a convergence of inputs from different sets of vestibular receptors. In particular, several neurons showed a pattern of response that indicated tht they received inputs from otolith receptors and ampullar receptors of the vertical canal. At low velocities of movement their response was positional but with inreasing velocity the magnitude of the response increased and there was a marked phase shift of the discharge towards head velocity. 5. Neurons responding to horizontal rotation often showed positional responses during lateral tilt. There were also indications of a convergence of ampullar inputs from both vertical and horizontal canals. 6. The neural pathways mediating these resonses are discussed in consideration of previous neuroanatomical and neurophysiological data. We consider it likely that several pathways may act to evoke the patterns of response observed, and a role of the cerebellar cortex is indicated.

Acoustic Maculae↗
PubMed1980

The dynamic discharge properties of oculomotor neurons in rabbits with intact and canal-plugged labyrinths during sinusoidal lateral tilt.

The characteristics of the control exerted by macular and ampullar vestibular receptors on oculomotor neurons (OMN) have been investigated by submitting unanesthetized, encéphale isolé rabbits, with intact and canal-plugged labyrinths, to sinusoidal lateral tilts of varying frequencies (0.013-0.2 Hz). For frequencies of tilt above 0.025 Hz, corresponding to peak angular accelerations suprathreshold for canal related vestibular neurons, both phase and sensitivity of the OMN response differ significantly in the two types of preparation. At lower frequencies of tilt the characteristics of the OMN response are, on the contrary, very similar, thus indicating that also in the intact animals the control of the vertical vestibulo-ocular reflex, in this frequency range, is exerted almost exclusively by the otoliths.

Animals↗
PubMed1979

Behavior of the oculomotor neurons discharge during sinusoidal lateral tilt in the rabbit.

The characteristics of the control exerted by macular and ampullar vestibular receptors on oculomotor neurons (OMN) have been investigated by submitting unanesthetized, encéphale isolé rabbits to sinusoidal lateral tilts of varying frequencies (0.013-0.2 Hz). The phase of the response exhibited a progressive shift towards head velocity with increasing frequencies of tilt. The sensitivity of the OMN significantly increased at frequencies above 0.025 Hz, corresponding to peak accelerations suprathreshold for canals related vestibular neurons. The convergent action of macular and ampullar vestibular receptors in the control of vertical eye movements is discussed in relation with stimulus frequency.

Animals↗
PubMed1978

Sensitivity of lateral cerebellar nucleus to macular stimulation in the rabbit.

Experiments were performed in decerebrate rabbits to determine the sensitivity of the lateral cerebellar nucleus (LCN) to macular stimulation. Twenty-three percent of the neurons recorded extracellularly in the LCN showed steady changes in their discharge rate during 20 degrees tilt in both directions of the medial plane. Most of these neurons exhibited an alpha- and beta-type of response. A few gamma-types, but no delta-types were observed. The units sensitive to tilt were restricted to the caudal half of the LCN. Some of these positionally sensitive neurons responded monosynaptically to ipsilateral labyrinthine stimulation, but many received a polysynaptic input. These units could be activated antidromically by stimulation of the oculomotor nucleus but at a very high intensity suggesting current spread to the nearby brachium conjunctivum fibers. These results exclude a role of the LCN in the disynaptic otolith-ocular reflex.

Acoustic Maculae↗