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At least 397 records · Page 22Linked to original sources
PubMed2002

Laryngeal effects of stimulation of rostral and ventral pons in the anaesthetized rat.

In order to study the importance of two pontine regions modulating laryngeal resistance, electrical current or microinjections of glutamate (10-30 nl, 1-3 nmol) were made into the pontine parabrachial complex and the A5 region in spontaneously breathing anaesthetized rats. Two distinct patterns of laryngeal and respiratory responses were elicited. An increase of subglottal pressure was accompanied with an expiratory facilitatory response consisted of a decrease in both respiratory rate and phrenic nerve activity. A decrease of subglottal pressure was accompanied with an inspiratory facilitatory response consisted of an increase in both respiratory rate and phrenic nerve activity. The modification of laryngeal calibre occurred during both respiratory phases in most cases. The concomitant cardiovascular changes of these responses were also analyzed. Controls using guanethidine to block autonomic responses which might interact with respiratory control were also made. Histological analysis of stimulation sites showed a topographical organization of these responses: laryngeal constriction was evoked from Kölliker-Fuse, medial parabrachial nuclei and A5 region, whilst the laryngeal dilation was evoked from the lateral parabrachial nucleus.

Action Potentials↗
PubMed2000

Connections of sympathetic fibres inside the cavernous sinus: a microanatomical study.

A microanatomical study has been designed to investigate the pattern of arrangement of the sympathetic fibres inside the cavernous sinus. The course of these fibres has been examined in 60 fresh specimens of parasellar region from autopsy cadavers. Apart from the thin branches arising at different intervals along its course, the sympathetic plexus of the carotid artery gives rise to a large division that usually joins the abducens nerve and leaves it to combine with the ophthalmic branch of the fifth. In 10% of specimens we have found a direct connection between sympathetic fibres and the ophthalmic branch of the trigeminal nerve. We did not recognise similar connections with oculomotor and trochlear nerves.

Abducens Nerve↗
PubMedDate not supplied

Pattern formation and rhythm generation in the ventral respiratory group.

1. There is increasing evidence that the kernel of the rhythm-generating circuitry for breathing is located within a discrete subregion of a column of respiratory neurons within the ventrolateral medulla referred to as the ventral respiratory group (VRG). It is less clear how this rhythm is transformed into the precise patterns appearing on the varied motor outflows. 2. Two different approaches were used to test whether subregions of the VRG have distinct roles in rhythm or pattern generation. In one, clusters of VRG neurons were activated or inactivated by pressure injection of small volumes of neuroactive agents to activate or inactivate groups of respiratory neurons and the resulting effects on respiratory rhythm and pattern were determined. The underlying assumption was that if rhythm and pattern are generated by neurons in different VRG subregions, then we should be able to identify regions where activation of neurons predominantly alters rhythm with little effect on pattern and other regions where pattern is altered with little effect on rhythm. 3. Based on the pattern of phrenic nerve responses to injection of an excitatory amino acid (DL-homocysteate), the VRG was divided into four subdivisions arranged along the rostrocaudal axis. Injections into the three rostral regions elicited changes in both respiratory rhythm and pattern. From rostral to caudal the regions included: (i) a rostral bradypnoea region, roughly associated with the Bötzinger complex; (ii) a dysrhythmia/tachypnoea area, roughly associated with the pre-Bötzinger complex (PBC); (iii) a second caudal bradypnoea area; and, most caudally, (iv) a region from which no detectable change in respiratory motor output was elicited. 4. In a second approach, the effect of unilateral lesions of one subregion, the PBC, on the Breuer-Hering reflex changes in rhythm were determined. Activation of this reflex by lung inflation shortens inspiration and lengthens expiration (TE). 5. Unilateral lesions in the PBC attenuated the reflex lengthening of TE, but did not change baseline respiratory rhythm. 6. These findings are consistent with the concept that the VRG is not functionally homogenous, but consists of rostrocaudally arranged subregions. Neurons within the so-called PBC appear to have a dominant role in rhythm generation. Nevertheless, neurons within other subregions contribute to both rhythm and pattern generation. Thus, at least at an anatomical level resolvable by pressure injection, there appears to be a significant overlap in the circuitry generating respiratory rhythm and pattern.

Animals↗
PubMed2004

Canceling planned action: an FMRI study of countermanding saccades.

We investigated the voluntary control of motor behavior by studying the process of deciding whether or not to execute a movement. We imaged the human dorsal cortex while subjects performed a countermanding task that allowed us to manipulate the probability that subjects would be able to cancel a planned saccade in response to an imperative stop signal. We modeled the behavioral data as a race between gaze-shifting mechanisms and gaze-holding mechanisms towards a finish line where a saccade is generated or canceled, and estimated that saccade cancelation took approximately 160 ms. The frontal eye fields showed greater activation on stop signal trials regardless of successful cancelation, suggesting coactivation of saccade and fixation mechanisms. The supplementary eye fields, however, distinguished between successful and unsuccessful cancelation, suggesting a role in monitoring performance. These oculomotor regions play distinct roles in the decision processes mediating saccadic choice.

Adolescent↗
PubMed1994

Dynamics of propagating waves in the olfactory network of a terrestrial mollusk: an electrical and optical study.

1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives ipsilateral axonal projections from superior and inferior noses. This network exhibits an approximately 0.7-Hz intrinsic oscillation in its local field potential (LFP). 2. Intracellular recordings show that the lobe contains at least two classes of neurons with activity phase locked to the oscillation. Neurons in one class produce periodic bursts of spikes, followed by a period of hyperpolarization and subsequently a depolarizing afterpotential. There is a small but significant chance for a second burst to occur during the depolarizing afterpotential; this leads to a double event in the LFP. Bursting neurons constitute approximately 10% of the neurons in the lobe. 3. Neurons in the other class fire infrequently and do not produce periodic bursts of action potentials. However, they receive strong, periodic inhibitory input during every event in the LFP. These nonbursting cells constitute the major fraction of neurons in the lobe. There is a clear correlation between the periodic burst of action potentials in the bursting neurons and the hyperpolarization seen in nonbursting neurons. 4. Optical techniques are used to image the spatially averaged transmembrane potentials in preparations stained with voltage-sensitive dyes. The results of simultaneous optical and electrical measurements show that the major part of the optical signal can be interpreted as a superposition of the intracellular signals arising from the bursting and nonbursting neurons. 5. Successive images of the entire PC lobe show waves of electrical activity that span the width of the lobe and travel its full length along a longitudinal axis. The direction of propagation in the unperturbed lobe is always from the distal to the proximal end. The wavelength varies between preparations but is on the order of the length of the preparation. 6. One-dimensional images along the longitudinal axis of the lobe are used to construct a space-time map of the optical activity, from which we calculate the absolute contribution of bursting and nonbursting neurons to the optical signal. The contribution of the intracellular signals from the two cell types appears to vary systematically across the lobe; bursting cells dominate at middle and proximal locations, and nonbursting cells dominate at distal locations. 7. The direction and form of the waves can be perturbed either by microsurgical manipulation of the preparation or by chemical modulation of its synaptic and neuronal properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Testing models of the oculomotor velocity-to-position transformation.

1. Do neural computations in premotor circuits mirror the physical properties of the systems they control? In 1987, Tweed and Vilis showed that oculomotor theories where a neural integrator converts eye angular velocity commands into position commands cannot be correct, because angular position is not the integral of angular velocity. Recently Schnabolk and Raphan proposed that an angular velocity integrator is nevertheless used to generate tonic commands in the oculomotor system. Here we test the Schnabolk-Raphan (S-R) model against Tweed and Vilis's quaternion (Q) model of the velocity to position transformation. 2. The S-R model predicts large (up to 7 degrees) transient (approximately 700 ms) deviations ("blips") in torsional eye position during attempted horizontal and vertical saccades. The Q model predicts no blips. Search coil recordings of saccades by 7 normal human subjects showed no large blips. 3. For approximately 200 saccades by each subject, we plotted the area under the torsional blip versus the product of saccade eccentricity and magnitude. According to the S-R model, this graph should form a straight line with slope 1.00. According to the Q model, the slope should be zero. Measured slopes averaged 0.016 (range -0.073 to 0.061) for saccade targets at 20 degrees eccentricity and 0.040 (range 0.004-0.076) for targets at 40 degrees. 4. No parameter change can significantly improve the S-R model, but lowering one parameter eradicates the tiny inaccuracy in the Q model. We show that the fundamental reason for the S-R model's failure is its use of a commutative controller to steer a noncommutative plant.

Attention↗
PubMed2005

Detecting activity in olfactory bulb glomeruli with astrocyte recording.

In the olfactory bulb, axons of olfactory sensory neurons (OSNs) expressing the same olfactory receptor converge on specific glomeruli. These afferents form axodendritic synapses with mitral/tufted and periglomerular cell dendrites, whereas the dendrites of mitral/tufted cells and periglomerular interneurons form dendrodendritic synapses. The two types of intraglomerular synapses appear to be spatially isolated in subcompartments delineated by astrocyte processes. Because each astrocyte sends processes into a single glomerulus, we used astrocyte recording as an intraglomerular detector of neuronal activity. In glomerular astrocytes, a single shock in the olfactory nerve layer evoked a prolonged inward current, the major part of which was attributable to a barium-sensitive potassium current. The K+ current closely reflected the time course of depolarization of mitral/tufted cells, indicating that K+ accumulation mainly reflects the activity of mitral/tufted cells. The astrocyte K+ current was dependent on AMPA and NMDA receptors in mitral/tufted cells as well as on a previously undescribed metabotropic glutamate receptor 1 component. Block of the K+ current with barium unmasked a synaptic glutamate transporter current. Perhaps surprisingly, the transporter current had components caused by glutamate released at both olfactory nerve terminals and mitral/tufted cell dendrites. The time course of the transporter currents suggested that rapid synchronous glutamate release at OSN terminals triggers asynchronous glutamate release from mitral/tufted cells. Glomerular astrocyte recording provides a sensitive means to examine functional compartmentalization within and between olfactory bulb glomeruli.

Animals↗
PubMed1999

Spontaneous network activity transiently depresses synaptic transmission in the embryonic chick spinal cord.

We examined the effects of spontaneous or evoked episodes of rhythmic activity on synaptic transmission in several spinal pathways of embryonic day 9-12 chick embryos. We compared the amplitude of synaptic potentials evoked by stimulation of the ventrolateral funiculus (VLF), the dorsal or ventral roots, before and after episodes of activity. With the exception of the short-latency responses evoked by dorsal root stimulation, the potentials were briefly potentiated and then reduced for several minutes after an episode of rhythmic activity. Their amplitude progressively recovered in the interval between successive episodes. The lack of post-episode depression in the short-latency component of the dorsal root evoked responses is probably attributable to the absence of firing in cut muscle afferents during an episode of activity. The post-episode depression of VLF-evoked potentials was mimicked by prolonged stimulation of the VLF, subthreshold for an episode of activity. By contrast, antidromically induced motoneuron firing and the accompanying calcium entry did not depress VLF-evoked potentials recorded from the stimulated ventral root. In addition, post-episode depression of VLF-evoked synaptic currents was observed in voltage-clamped spinal neurons. Collectively, these findings suggest that somatic postsynaptic activity and calcium entry are not required for the depression. We propose instead that the mechanism may involve a form of long-lasting activity-induced synaptic depression, possibly a combination of transmitter depletion and ligand-induced changes in the postsynaptic current accompanying transmitter release. This activity-dependent depression appears to be an important mechanism underlying the occurrence of spontaneous activity in developing spinal networks.

Animals↗
PubMed2005

Central nervous mechanisms in the generation of the pattern of breathing.

The role of the Bötzinger complex (BötC) and the pre-Bötzinger complex (pre-BötC) in the genesis of the breathing pattern was investigated in anesthetized, vagotomized, paralysed and artificially ventilated rabbits making use of bilateral microinjections of kainic acid (KA) and excitatory amino acid (EAA) receptor antagonists. KA microinjections into either the BötC or the pre-BötC transiently eliminated respiratory rhythmicity in the presence of tonic phrenic activity (tonic apnea). Rhythmic activity resumed as low-amplitude, high-frequency irregular oscillations, superimposed on tonic inspiratory activity and displayed a progressive, although incomplete recovery. Microinjections of kynurenic acid (KYN) and D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) into the BötC caused a pattern of breathing characterized by low-amplitude, high-frequency irregular oscillations and subsequently tonic apnea. Responses to KYN and D-AP5 in the pre-BötC were similar, although less pronounced than those elicited by these drugs in the BötC and never characterized by tonic apnea. Microinjections of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) into the BötC and the pre-BötC induced much less intense responses mainly consisting of increases in respiratory frequency. The results show that the investigated medullary regions play a prominent role in the genesis of the normal pattern of breathing through the endogenous activation of EAA receptors.

Action Potentials↗
PubMed1989

Immunocytological localization of pedal peptide in the central nervous system and periphery of Aplysia.

Immunocytology using antisera raised to conjugated pedal peptide (Pep) was used to localize the peptide in the CNS and periphery of Aplysia. A total of over 200 neurons in the CNS exhibited Pep-like immunoreactivity. As expected from results presented in the previous paper, immunoreactive neurons were heavily concentrated in the pedal ganglia, primarily in a broad ribbon comprised of about 60 large contiguous neurons on the dorsal side of each ganglion. Smaller and less numerous immunoreactive neurons were found in the other ganglia. A number of neurons primarily located in the abdominal ganglia had dense networks of immunoreactive varicose fibers surrounding their cell bodies. Many immunoreactive axons were observed in peripheral nerves, particularly those nerves leaving the pedal ganglia. Analyses of sections of body wall indicated that Pep-like immunoreactivity was localized to a series of varicose axons that appeared to be associated with vascular spaces, muscle fibers, and other large cells. These axons likely arise from pedal ganglion nerves that were shown to transport large amounts of 35S-labeled Pep to the periphery. These results suggest that Pep is a transmitter-like neuropeptide that is likely to have a number of important physiological actions in Aplysia.

Animals↗
PubMed1994

The oculomotor neural integrator uses a behavior-related coordinate system.

Coordinate systems are a central issue in computational neuroscience: are they explicitly represented at some reductive level of brain function, and if so, are they only trivial products of associated anatomic geometries? This investigation examined these questions in the neural network that holds eye position, the so-called oculomotor integrator. Since neural activity in the integrator is behaviorally constrained by Listing's law to encode horizontal and vertical eye positions within Listing's plane and zero rotation about the orthogonal torsional axis, it was hypothesized that any integrator coordinate system would be developmentally predisposed to align with Listing's plane. A test for this hypothesis was developed with the use of a kinematically correct model of the three-dimensional saccade generator. Three mathematical integrators were used to represent the neuron populations that control torsional, vertical, and horizontal eye position. Simulated failure of the torsional and vertical integrators produced eye position drift that was parallel to the horizontal plane containing the intrinsic coordinate axes for these components. Furthermore, this drift settled toward a resting range parallel to the intrinsic vertical coordinate axis (for horizontal rotation). To experimentally identify these intrinsic population coordinates, three-dimensional eye positions were measured in four Macaca fascicularis after injection of muscimol into the mesencephalic interstitial nucleus of Cajal (INC), a technique that disrupts the torsional and vertical integrators (Crawford et al., 1991). INC inactivation produced exponential, position-dependent decay in vertical and torsional eye position. There was no position-dependent horizontal drift, but in the original coordinate system (defined arbitrarily by the measurement apparatus) there was a constant-direction horizontal drift. However, this extraneous horizontal drift was eliminated when the data were transformed into a coordinate system that aligned with Listing's plane. The direction of torsional drift correlated well (r = 0.85), across all experiments, with the normal to Listing's plane. On average, these two directions were only 0.06 degrees from perfect alignment. In contrast, drift direction did not correlate with stereotaxic coordinates (r = 0.10). Furthermore, the drift settled toward a range parallel to and correlated with Listing's plane (r = 0.94), whereas this range did not correlate well with stereotaxic coordinates (r = 0.02). On average, the resting range was aligned within 0.98 degrees of Listing's plane. Finally, this resting range was near orthogonal (average 91.9 degrees across all experiments) to the direction of torsional drift. These results show that integrator cell populations use an orthogonal, craniotopic coordinate system that aligns with Listing's plane.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Detection of structural damage from glaucoma with confocal laser image analysis.

PURPOSE: To determine which structural optic nerve head parameters measured with confocal scanning laser image analysis that best discriminate between normal persons and those with glaucoma. METHODS: One randomly selected eye of 53 patients with early open-angle glaucoma (average visual field mean deviation = -4.8 dB) and of 43 age-, race-, and refractive error-matched normal subjects were studied. The performance of nine structural measures was evaluated with linear multivariate analysis and a neural network: cup area, cup to disc area ratio, rim area, height variation contour, cup volume, rim volume, cup shape measure, mean retinal nerve fiber layer thickness, and retinal nerve fiber layer cross-section area. A discriminant function was derived with two thirds of the sample and its discriminant power tested on the remaining one third. This was repeated twice so that the entire sample was used for training and testing. A neural network was trained and tested in the same way. Stereoscopic color optic nerve photographs of the same eyes were evaluated qualitatively by three experienced, masked observers. Receiver operating characteristic (ROC) curves of discriminant function, neural network results, and qualitative evaluation were plotted. Comparisons of the areas under the ROC curves were performed with nonparametric statistics. RESULTS: There were statistically significant differences between the normal and glaucoma groups for all measures (P < or = 0.007) except for height variation contour, mean retinal nerve fiber layer thickness, and retinal nerve fiber layer cross-section area. Cup shape measure provided the single best measure to distinguish between normal subjects and those with early glaucoma and had a diagnostic precision of 84%. Neural network diagnostic precision, when all measures were used, was 92% and decreased to 82% when cup shape measure was omitted. The area under the ROC curve when all measures were combined was 0.94; it was significantly lower (P = 0.04) when cup shape measure was omitted (area = 0.84). The area under the ROC curve for qualitative optic disc evaluation by experienced observers was 0.93. There was no statistically significant difference between qualitative evaluation and neural network performance (P = 0.80). CONCLUSIONS: Cup shape measure, the statistical third moment of the distribution of depth values of the optic nerve head obtained with confocal laser image analysis, can be used to discriminate between normal persons and those with early glaucomatous damage with high diagnostic precision.

Female↗