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Biomedical subjects

H Vanegas

Publications and source records attributed to H Vanegas.

At least 37 records · Page 2Linked to original sources
PubMed1995

Anti-nociception induced by systemic or PAG-microinjected lysine-acetylsalicylate in rats. Effects on tail-flick related activity of medullary off- and on-cells.

Previous experiments using metamizol have shown that this non-steroidal anti-inflammatory drug (NSAID) produces a central anti-nociceptive effect probably through neural substrates that also support the analgesic effects of opiates, such as the periaqueductal grey matter (PAG) and the off- and on-cells of the rostral ventromedial medulla (RVM). Off- and on-cells have been postulated to respectively inhibit and facilitate nociceptive transmission, since the heat-elicited tail flick reflex (TF) occurs only after off-cells have decreased (pause), and on-cells, have increased (burst) their activity. The aim of the present study was to examine whether the effect of metamizol upon TF and off- and on-cells responses could be generalized to other NSAIDs such as, in this case, lysine-acetylsalicylate (LASA). Fifty-nine off- and on-cells of the RVM were recorded in lightly anaesthetized rats. Systemic administration (200 and 300 mg/kg) or PAG microinjection (30, 50 and 100 micrograms) of LASA caused retardation of the heat-elicited off-cell pause, on-cell burst and the corresponding TF. Neuronal responses and TF retained their mutual time relationship but shifted simultaneously toward longer latencies. This anti-nociceptive effect of LASA was dose-dependent, present 5 min after administration and reached a maximum in 30 min for both administration methods. These data confirm that analgesics typically defined as peripherally-acting, such as metamizol and LASA in this study, may also have an anti-nociceptive effect by acting directly upon PAG, and suggest that this central effect involves the RVM off- and on-cells.

Action Potentials↗
PubMed1993

Concurrent effect of morphine on thalamic nociceptive neurons and medullary on- and off-cells.

On- and off-cells of the rostral ventromedial medulla project to the spinal cord, where off-cells are postulated ot inhibit, and on-cells to facilitate, nociceptive transmission. In the present experiments, unitary recordings were made from ventrobasal (VB) thalamic neurons and, simultaneously, on- or off-cells in lightly anesthetized rats. When the tail was heated (45-55 degrees C) off-cells stopped firing (pause) and on-cells began to fire (burst) 0.5-0.6s before VB neurons responded to the tail stimulus. Administration of morphine sulfate (2 mg/kg i.v.) concurrently prevented the off-cell pause, the on-cell burst an the VB neuronal response. Naloxone (1 mg/kg i.v.) reversed these effects. The results are consistent with the notion that prevention of the off-cell pause and the on-cell burst by morphine is responsible for the lack of nociceptive information flow towards the thalamus.

Animals↗
PubMed1990

"Off" and "on" cells of the medulla oblongata as possible mediators of analgesia produced by mesencephalic and diencephalic stimulation in rats.

The present study shows the effects of electrical' stimulation of mesencephalic and diencephalic structures on the activity of two types of neuron from the rostral ventromedial medulla, which are related to the nocifensive reflex known as tail flick response (TF). One type of neuron, the off-cell, abruptly stops firing immediately before the tail is flicked, while the other type, the on-cell, increases firing just before the flick. When electrical stimulation was applied to mesencephalic and diencephalic structures the TF was inhibited and, simultaneously, both kinds of cells showed increments in their activities. On average, this increment was 81 +/- 22.09% for the off-cells, and 1563 +/- 257.66% for the on-cells. Quantitative analysis showed a directly proportional relationship between the activation of the firing rate of both kinds of cells and the intensity of the stimulation currents. Also, when the stimulation electrode was positioned more rostrally in the brain, greater currents were needed to reach the threshold of analgesia. The present work contributes to a large body of evidence indicating that off-cells, on-cells, or both, are involved in the complex mechanism of the control of nociceptive transmission and nocifensive reflexes.

Analgesia↗
PubMed1989

Tooth pulp stimulation advances both medullary off-cell pause and tail flick.

It has been postulated that the so-called off-cells of nucleus raphe magnus and adjacent structures in the rat are the output elements of a system which inhibits nociceptive transmission at the spinal cord. Off-cells stop firing about 0.4 s before the tail flick reflex (TF) elicited by the application of noxious heat to the tail. When continuous off-cell activity is induced by either morphine injection or periaqueductal gray stimulation, the TF is delayed. The present results show that electrical stimulation of the tooth pulp (TP) causes the off-cells to stop firing. Furthermore, when TP is stimulated during tail heating and before the expected time for TF, off-cells stop firing earlier and the TF occurs also earlier. This supports the notion that off-cells inhibit nociceptive transmission.

Animals↗
PubMed1984

Diameters and terminal patterns of retinofugal axons in their target areas: an HRP study in two teleosts (Sebastiscus and Navodon).

Studies in various vertebrate classes, particularly amphibians and mammals, have revealed that retinal ganglion cells with different functional properties project by means of axons of correspondingly different diameters onto specific target regions. Whether a similar pattern exists in teleosts is partly investigated in the present study. HRP was injected into the optic nerve of Sebastiscus and Navodon. The calibers of intraretinal HRP-labeled axons were classed as fine (ca. 0.8 micron), medium (ca. 1.3 micron), and coarse (ca. 2.5 microns). The calibers of HRP-labeled retinofugal axons were then determined in their target areas, and these can be summarized as follows: Optic hypothalamus: fine, medium. Lateral geniculate nucleus: fine. Dorsolateral thalamic nucleus: fine, medium. Area pretectalis: fine. Nucleus of the posterior commissure: fine, medium. Area ventralis lateralis, contralateral: fine, medium, coarse; ipsilateral: coarse. Optic tectum, stratum opticum: fine, medium; stratum fibrosum et griseum superficiale: fine, medium, coarse, segregated in sublayers; stratum album centrale: fine, medium, coarse. Therefore, fine fibers were found to reach all target areas except the ipsilateral area ventralis lateralis, and these were the only fibers found in the lateral geniculate nucleus, area pretectalis, and stratum griseum centrale of the optic tectum. Coarse fibers, on the other hand, were found only in the area ventralis lateralis and the optic tectum (stratum fibrosum et griseum superficiale and stratum album centrale). Terminal patterns of these fibers were also studied. Most fine fibers take tortuous courses giving off a few branches and terminate with many varicosities, and medium and coarse fibers give off several finer branches and terminate with bulbous swellings. The physiological significance of these findings is discussed. In addition, retrogradely labeled (retinopetal) cells were found in the olfactory bulb and the area ventralis pars ventralis of the telencephalon, as well as in the preoptic area and the dorsolateral thalamic nucleus.

Animals↗
PubMed1984

Midbrain stimulation inhibits tail-flick only at currents sufficient to excite rostral medullary neurons.

The effects of midbrain electrical stimulation on the activity of tail-flick (TF) related neurons in the rostral ventromedial medulla (RVM) were studied. Neurons whose activity either decreased (off-cells) or increased (on-cells) immediately prior to TF were examined. Of 31 off- and on-cells, 26 (84%) showed increased activity during midbrain stimulation sufficient to suppress the TF. Furthermore, in 21 of these cells, the threshold for activation was identical to the threshold for TF suppression, and in the other 5 cells the threshold difference was less than or equal to 5 microA. This study provides evidence that off-and on-cells in the RVM mediate the antinociceptive actions of midbrain stimulation.

Animals↗
PubMed1984

Tail-flick related activity in medullospinal neurons.

Using the classification system of Fields et al. 131 neurons in the rostral ventromedial medulla (RVM) of lightly anesthetized rats were divided into 3 groups according to their response during tail-flick (TF) testing: those with an abrupt increase in activity prior to TF (on-cells); those with a sudden pause in activity prior to TF (off-cells); those with no change in activity prior to TF (neutral cells). Collision testing was performed using a cervical spinal cord stimulating electrode to determine whether these neurons projected to the cord. Conduction velocities were determined for all cord-projecting neurons. All 3 cell types projected to the cord and approximately 38% of cord-projecting neurons were flick-related (off-or on-cells). All projecting neurons were within or immediately adjacent to the nucleus raphe magnus. The mean conduction velocity of on-cell axons (17.7 m/s) was significantly greater than that of off-cell axons (10.7 m/s) and neutral cell axons (12.4 m/s). Conduction velocities for all cells were within the range for myelinated axons. These findings support the hypothesis that off-and on-cells in the RVM play a significant role in pain modulation at the spinal cord level.

Animals↗
PubMed1984

Visual receptive thalamopetal neurons in the optic tectum of teleosts (Holocentridae).

Tectal neurons previously known to receive retinofugal input were herein shown to project to the nucleus prethalamicus. Following HRP injections into the nucleus prethalamicus, pyriform neurons in the stratum periventriculare and stratum album centrale, and fusiform neurons in the stratum griseum centrale, were retrogradely labeled. Because the labeled types of neurons have been characterized as the main visual receptive neurons of the optic tectum, and because the nucleus prethalamicus of teleosts projects to the telencephalon, this nucleus can now be considered homologous to the nucleus rotundus of reptiles and birds and to the nucleus lateralis posterior-pulvinar complex of mammals, that is, it provides a relay for retinotectal visual input to the telencephalon. Orthogradely labeled terminals as well as retrogradely labeled neurons were also found in the dorsal area of the telencephalon. The tecto-prethalamotelencephalic projections are only ipsilateral.

Animals↗
PubMed1984

Visual (optokinetic), somesthetic and vestibular inputs to the frog cerebellum.

Unitary response to visual (optokinetic), somesthetic (neck and limb) and vestibular stimulation were recorded from the Purkinje cell layer throughout most of the dorsal surface of the frog cerebellum. Simple spike activity in Purkinje cells and activity from cells without complex spikes were considered. Optokinetic responses (types I-III) were restricted to the dorsal rim and auricular lobes. Units were sensitive to very small velocity of optokinetic cylinder rotation (0.02-0.03 degrees/s) with peak sensitivity at about 1 degree/s. On the average an approximately linear relation of response amplitude to stimulus velocity was observed from 0.02 to 1 degree/s. The response progressively diminished above 1 degree/s to become very small at 30 degrees/s. Asymmetric response and silencing of firing during part of the cycle were nonlinearities observed with sinusoidal optokinetic stimulation in the range of 0.02-1 Hz, +/- 5-10 degrees (peak velocities 0.8-30 degrees/s). Somesthetic responses were recorded throughout most of the corpus cerebelli proper but the strongest input was to rostral regions. No somatotopic arrangement was found. Rather, convergence from more than one limb and neck was relatively common. Adaptation to successive cycles of stimulation was characteristic of somesthetic responses. Vestibular responses (type I-IV) were recorded throughout most of the explored area but the strongest input was to the dorsal rim and auricular lobes. From the analysis of unitary activity, the dorsal rim and auricular lobes are shown to be functionally linked to the vestibular and optokinetic systems whereas the explored part of the corpus is linked to the somesthetic and vestibular systems.

Animals↗
PubMed1984

Visual (optokinetic) and somesthetic inputs to the cerebellum of bilaterally labyrinthectomized frogs.

Unitary responses to visual (optokinetic) and somesthetic (cutaneous and propioceptive ) stimulation were recorded from the Purkinje cell layer of the cerebellum of acute (up to 30 h) and chronic (30-90 days) bilaterially labyrinthectomized frogs. Simple spikes from Purkinje cells as well as activity from cells without complex spikes were considered in this paper. The properties of the response and the distribution (restricted to the dorsal rim and auricular lobes) of the units sensitive to optokinetic stimulation of labyrinthectomized frogs, both acute and chronic, were similar to those previously reported for normal animals. The properties of the responses to somesthetic neck and limb stimulation remained similar to those of normal animals. However, there was an increase in the number of units responsive to somesthetic stimulation within the dorsal half of the corpus cerebelli (including the dorsal rim), a region experimentally deprived of vestibular afferents, neck responsive units were 33% of the total in acutely and 61% in chronically labyrinthectomized animals (compared to 5% in normal). Limb responsive units were 49% in acute and 65% in chronic animals (compared to 12% in normal). A consequence of the increase in somesthetic input was convergence of optokinetic and somesthetic inputs at the level of single units within the dorsal rim, totally absent before the lesion. The results suggest that the somesthetic spinal input might substitute for at least some features of the vestibular input to the cerebellum in bilaterally labyrinthectomized frogs.

Action Potentials↗
PubMed1983

Cytoarchitecture and ultrastructure of nucleus prethalamicus, with special reference to degenerating afferents from optic tectum and telencephalon, in a teleost (Holocentrus ascensionis).

Histological structure and neuronal geometry of the nucleus prethalamicus of holocentrid teleosts, which is homologous to the nucleus rotundus of reptiles and birds and to the nucleus lateralis posterior-pulvinar complex of mammals, were studied by means of the Bodian, Nissl, toluidine blue, and Golgi methods. Synaptic terminals were classified electron microscopically, and terminal types originating from the telencephalon and the optic tectum were determined by electron microscopy in degeneration experiments. The nucleus prethalamicus is composed of four layers, in the following order from medial to lateral: a small-cell layer, a plexiform layer, a large-cell layer, and a marginal layer. Six types of terminals (U, L, Sp, Sd, F, and P) were distinguished in the nucleus, and the distribution pattern for each type of terminal was determined by counting its relative number in each layer. Sp terminals make synaptic contacts with small-cell dendrites or somata in the small-cell layer, and degenerate after telencephalic ablations. Sd terminals synapse exclusively with spines of large-cell dendrites in both marginal and large-cell layers, and degenerate after tectal ablations. Because only large neurons have been labeled after HRP injections into the telencephalon (Ito et al., '80, '82; Ebbesson, '80; Murakami et al., '83), it is considered that these neurons relay visual information from the optic tectum onto the telencephalon. It is hypothesized that the small neurons in the nucleus, which receive telencephalic input, might modulate the large neurons' relay function.

Animals↗
PubMed1983

Morphological aspects of the teleostean visual system: a review.

This review is concerned with results of research carried out in the last two decades regarding visual pathways and centers in teleosts. It covers neither morphology of the retina nor development and plasticity. The optic nerve is considered in terms of axonal composition and retinotopic organization. The connections to the retina and from the retina are subsequently reviewed, and a general scheme is proposed for the retinofugal targets in thalamus and pretectum. The tectum opticum is then reviewed as regards its afferent connections from retina, telencephalon, diencephalon, mesencephalon and brainstem, with details on distribution of terminals, cell types contacted and synaptic structure. The efferent tectal connections are reviewed next, including their plausible cells of origin. Finally, a general diagram of the teleostean visual system is presented, and several circuits within this diagram are emphasized and discussed.

Afferent Pathways↗
PubMed1981

Identification of pericellular baskets in the cat striate cortex: light and electron microscopic observations after uptake of horseradish peroxidase.

This paper presents one of the few descriptions and the first light and electron microscopic reconstruction of a pericellular basket in the cat striate cortex. A pericellular basket and its related pyramidal cell in cortical layer V were labelled by nearby injection of horseradish peroxidase. The basket and pyramidal cell, contained in a cortical transverse section embedded in plastic, were analysed by light microscopy. Subsequently, similarly transverse serial sections of 4 micrometer thickness were cut through a basket and pyramidal cell, and these sections were also documented by light microscopy. Finally, serial ultrathin sections were made from each 4 micrometer section and analysed electron microscopically. Graphic reconstructions of the basket and its pyramidal cell were then made from the 4 micrometer and ultrathin sections. The basket had the characteristic appearance of axon stalks and terminal boutons intertwined around the soma and basal dendritic processes of the pyramid. Basket boutons contained mitochondria and a large number of tightly packed dark vesicles, round or oval in shape. Subsynaptic densities were discrete and extended for only a fraction of the basket bouton/pyramidal cell contact. With some reservations, these synapses can be classed as symmetrical. The basket was connected to several axons, and these were myelinated right to the level of the stalks and boutons. This was an unexpected finding since pericellular baskets have been shown to arise from local interneurons.

Animals↗
PubMed1980

Cytoarchitecture of the optic tectum of the squirrelfish, Holocentrus.

The Holocentrus has large eyes and a well-developed optic tectum. Nissl and fibers stains and various Golgi techniques show that the optic tectum of Holocentrus has six strata which can be subdivided into 14 alternating cell and fiber layers, some of which have additional organization. The stratum marginale (SM) is especially impressive in this fish and contains dendrites of pyramidal neurons, marginal fibers from torus longitudinalis, and axon-like processes (the SM ascending axons) from cells located in the stratum griseum centrale (SGC). Stratum opticum (SO) and stratum fibrosum et griseum superficiale (SFGS) have many small neurons with limited dendritic fields. The large, so-called pyramidal cell of SFGS has an extensive dendritic tree in SM and descending dendrites and axon to SGC. The latter has a variety of neurons with large dendritic fields in various layers of the tectum; the most distinctive, however, is the large fusiform neuron with its shepherd's crook axon. This stratum also has a dense layer of neuropil, the internal plexiform layer. Stratum album centrale (SAC) is primarily a fibrous layer, and stratum periventriculare (SPV) is a dense cellular area with the upper portion containing neuronal types also found in SGC and different from the typical neurons found in SPV. The latter have a major ascending branch with various dendritic patterns, and often do not have an identifiable axon; however, some of these cells have extensive branches throughout SFGS with an axon-like appearance. Some general conclusions were made about the functional significance of the various tectal layers and cell types.

Animals↗
PubMed1979

Responses to stimulation of marginal fibers in the teleostean optic tectum.

The marginal fibers (mf) constitute a major fiber component of the teleostean optic tectum, and this report deals with the physiological properties of these fibers and their postsynaptic elements. The mf are unmyelinated axons which originate at the torus longitudinalis and run lateralwards, parallel to one another, along the tectum's most superficial layer (stratum marginale). Here they synapse upon the dendritic arborizations of the pyramidal (p) neurons. These arborizations originate from a single apical dendritic shaft which, near the soma, receives retinofugal axon terminals. The p-neurons also have a basal dendritic shaft and a descending axon, both of which branch out horizontally at the stratum griseum centrale (SGC). The mf were stimulated through surface microelectrodes, and field potentials were recorded on-beam throughout the tectal thickness by means of micropipettes. The mf action potential (M-spike) may show two negative subpeaks which propagate at 0.20 and 0.16 m/s. Its refractory period is followed by a period of increased amplitude and decreased latency. The M-spike is followed by a series of slow waves, namely: (a) The S-wave, which probably represents the monosynaptic depolarization of the p-neuron's apical arbor; (b) The N-wave which possibly represents an active current sink at the point where these dendritic arborizations merge into the apical dendritic shaft; (c) The D-wave, recorded at the SGC, which possibly represents the activation of the p-neuron's axon and terminals (and perhpas also basal dendritic shaft and branches); and (d) the L-wave, which might represent a later depolarization of the p-neuron's apical arborizations. Morphologically and electrophysiologically, there are several similarities between the tectal mf/p-neuron system and the cerebellar parallel fiber/Purkinje cell system.

Animals↗