Biomedical subjects

M A Castro-Alamancos

Publications and source records attributed to M A Castro-Alamancos.

29 records · Page 2Linked to original sources

PubMed1994

Learning of the conditioned eye-blink response is impaired by an antisense insulin-like growth factor I oligonucleotide.

The cerebellum is thought to be critically involved in learning and retention of several types of classically conditioned motor responses. We investigated whether insulin-like growth factor I (IGF-I) may constitute an intercellular mediator of a motor learning task because previous findings indicated that IGF-I from the inferior olive modulates glutamate-induced gamma-aminobutyric acid release by Purkinje cells in the cerebellar cortex. Synaptic plasticity of the Purkinje cell is thought to be instrumental in motor learning. We found that injection of an IGF-I antisense oligonucleotide in the inferior olive elicited a complete inhibition of conditioned eye-blink learning in freely moving rats. This blockage was reversible and recovered when the levels of cerebellar IGF-I returned to normal values. Injection of a sense oligonucleotide did not interfere with the acquisition of the conditioned response. On the other hand, retention of the conditioned response was not impaired by subsequent injection of the IGF-I antisense oligonucleotide, indicating that olivocerebellar IGF-I is essential for the acquisition of the conditioned eye-blink response but is not essential for its retention.

Animals↗

PubMed1994

Scopolamine induces recovery of shuttle box avoidance behavior after frontal cortex ablation.

The learning and reversal of shuttle box active avoidance behavior in animals with a bilateral frontal cortex ablation was investigated during and after scopolamine or pilocarpine treatment. Scopolamine facilitated the performance of the avoidance task in normal animals and in those with frontal cortex lesions and also increased the number of intertrial responses, while pilocarpine increased the deleterious effects of the lesions. Furthermore, in the absence of scopolamine, the animals previously treated with the drug showed that its beneficial effects persisted while the number of intertrial responses were no longer increased. The results indicate that the beneficial effects of scopolamine treatment on active avoidance behavior are independent from the effects observed on intertrial activity since only the former are observed after drug withdrawal. Therefore, scopolamine treatment seems to induce a long lasting recovery process in frontal cortex ablated animals.

Animals↗

PubMed1993

Long-term depression of glutamate-induced gamma-aminobutyric acid release in cerebellum by insulin-like growth factor I.

We tested the possibility that insulin-like growth factor I (IGF-I) acts as a neuromodulator in the adult cerebellar cortex since previous observations indicated that IGF-I is located in the olivo-cerebellar system encompassing the inferior olive and Purkinje cells. We found that conjoint administration of IGF-I and glutamate through a microdialysis probe stereotaxically implanted into the cerebellar cortex and deep cerebellar nuclei greatly depressed the release of gamma-aminobutyric acid (GABA), which normally follows a glutamate pulse. This inhibition was dose-dependent and long-lasting. Moreover, the effect was specific for glutamate since KCl-induced GABA release was not modified by IGF-I. Basic fibroblast growth factor, another growth-related peptide present in the cerebellum, did not alter the response of GABA to glutamate stimulation. In addition, electrical stimulation of the inferior olivary complex significantly raised IGF-I levels in the cerebellar cortex. Interestingly, when the inferior olive was stimulated in conjunction with glutamate administration, GABA release by cerebellar cells in response to subsequent glutamate pulses was depressed in a manner reminiscent of that seen after IGF-I. These findings indicate that IGF-I produces a long-lasting depression of GABA release by Purkinje cells in response to glutamate. IGF-I might be present in climbing fiber terminals and/or cells within the cerebellar cortex and thereby might affect Purkinje cell function. Whether this IGF-I-induced impairment of glutamate stimulation of Purkinje cells underlies functionally plastic processes such as long-term depression is open to question.

Animals↗

PubMed1993

Active avoidance behavior using pontine nucleus stimulation as a conditioned stimulus in the rat.

Five groups of rats were trained in an active avoidance task in a shuttle box with different conditioned stimuli. Animals with either a light-conditioned stimulus or with electrical stimulation of the ventral pontine nucleus as a conditioned stimulus rapidly learned to avoid an aversive event, while those with no conditioned stimulus, with electrical stimulation of the lateral pontine nucleus or the medial lemniscus did not learn to avoid. Therefore, stimulation of a specific subdivision of the pontine nucleus is as effective as a light-conditioned stimulus to learn an active avoidance task.

Animals↗

PubMed1993

Motor activity induced by disinhibition of the primary motor cortex of the rat is blocked by a non-NMDA glutamate receptor antagonist.

Application of a GABAA (gamma-aminobutyric acid-A) receptor antagonist through a microdialysis probe into the forelimb primary motor cortex of ketamine-anesthetized rats induced electromyographic activity in the contralateral forelimb. This activity consisted of spontaneous forelimb movements with a frequency of 0.8 +/- 0.2 Hz. The motor activity induced by GABAA receptor blockade was suppressed by application through the dialysis probe of a non-NMDA (N-methyl-D-aspartate) receptor antagonist, but not by an NMDA receptor antagonist. Glutamate eliminated the blocking effect of the non-NMDA receptor antagonist upon GABAA receptor blockade mediated activity. In conclusion, the results show that an excitatory input to the motor cortical output is mediated through a non-NMDA receptor, therefore the effects of cortical disinhibition may be controlled by non-NMDA receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1993

Reversal of paw preference after ablation of the preferred forelimb primary motor cortex representation of the rat depends on the size of the forelimb representation.

Animals were tested for forelimb preference in a grasp or in a force task before microstimulation mapping of the primary motor cortex contralateral to the preferred forelimb. The size and location of the preferred forelimb primary motor cortex representation was determined and ablated. Seven days later, forelimb preference was again evaluated. Reversal of the initial preference after cortical ablation depended on the size of the preferred forelimb primary motor cortex representation. The mean size of the forelimb representation of the animals that immediately reversed forelimb preference after the cortical ablation was significantly smaller than the mean size of the representation of the animals that did not reverse forelimb preference in three consecutive tests seven days after the lesion. In another experiment, the size, location, and threshold currents of the forelimb representations were evaluated bilaterally before the forelimb preference test. The mean size of the preferred representations did not differ from the mean size of the non-preferred representations. However, when the primary motor cortex representation of the preferred forelimb was ablated, reversal of the initial preference depended, as in the previous experiment, on the size of the forelimb representation. In conclusion, reversal of forelimb preference after ablation of the preferred forelimb primary motor cortex representation depends on the size of the forelimb representation. Moreover, forelimb preference in a behavioral task is not associated with a larger forelimb representation in the contralateral primary motor cortex.

Animals↗

PubMed1992

Facilitation and recovery of shuttle box avoidance behavior after frontal cortex lesions is induced by a contingent electrical stimulation in the ventral tegmental nucleus.

A bilateral ablation of the frontal cortex was performed in rats before and after training in an active avoidance task in a shuttle box. Animals with this lesion showed an impairment in learning and in the reversal of the avoidance task. If the animals with the lesion were implanted with an electrode in the ventral tegmental nucleus and received an electrical stimulation in this area contingent to a correct response (avoidance or escape response) in the behavioral task, they did not show any impairment in the performance of the task. Furthermore, the effect of the stimulation persisted after it was retrieved. The present findings indicate that the motivational and cue properties of the electrical stimulation of the ventral tegmental nucleus may serve to facilitate learning and reversal in an avoidance task and to induce at the long term a recovery process in animals in which the frontal cortex has been ablated. Therefore, this method may be useful to study the adaptative changes which take place in the nervous system after recovery from brain damage occurs.

Animals↗

PubMed1992

Performance in an escape task induces fos-like immunoreactivity in a specific area of the motor cortex of the rat.

The expression of the c-fos proto-oncogene was studied in two different areas of the motor cortex and in the hippocampus of the rat after performance in an escape task in a Skinner box. Performance in this task caused an increase in the number of cells showing fos-like immunoreactivity in layers V and VI of the forelimb motor-sensory cortex with respect to yoked animals which had received the same amount, frequency and duration of aversive stimulation and manipulation as the trained animals. Therefore, this increase is the specific effect of performing the behavioral task. In the hindlimb motor-sensory cortex there were no differences between the trained and the yoked animals in any of the cortical layers. No differences were observed in the dentate gyrus of the hippocampus between trained and yoked animals, while the control animals showed a much lower fos-like immunoreactivity. In conclusion, infragranular layers in the forelimb representation of the primary motor cortex become activated with respect to the expression of fos-like immunoreactivity after performance in an escape task in a Skinner box. This result is consistent with the idea that even in complex structures such as the cerebral cortex, specific trace systems become activated for the performance of complex behavioral tasks.

Analysis of Variance↗

PubMedDate not supplied

Short-term plasticity in thalamocortical pathways: cellular mechanisms and functional roles.

Information reaches the neocortex through different types of thalamocortical pathways. These differ in many morphological and physiological properties. One interesting aspect in which thalamocortical pathways differ is in their temporal dynamics, such as their short-term plasticity. Primary pathways display frequency-dependent depression, while secondary pathways display frequency-dependent enhancement. The cellular mechanisms underlying these dynamic responses involve pre- and post-synaptic and circuit properties. They may serve to synchronize, amplify and/or filter neural activity in neocortex depending on behavioral demands, and thus to adapt each pathway to its specific function.

Action Potentials↗

PubMedDate not supplied

[Thalamocortical dynamics: how do the thalamus and the neocortex communicate during the processing of information?].

INTRODUCTION AND DEVELOPMENT: The thalamus is the gateway to the neocortex. Most of the information that reaches the neocortex is transmitted through thalamocortical fibres. The neocortex, in turn, sends massive feedback to the thalamus through corticothalamic fibres. The sensory input reaches the thalamus by means of the primary sensory fibres. When the properties of these pathways are explored, they are found to present specific response characteristics. These studies have generally been conducted during anaesthesia or other quiescent states. Yet when the properties of these synaptic connections are explored in the active states typical of information processing, their responses are substantially different. CONCLUSION: These changes appear to be necessary to set the pathways of the thalamocortical system in a state of sensory input processing and, therefore, could account for the transformations that take place in order to sustain attentional and perceptive processes.

Action Potentials↗

PubMedDate not supplied

[Interactions between the immune system and the neuroendocrine system. Implications of the hypothalamo-hypophyseal-adrenal axis].

The immune and neuroendocrine systems are now recognized to be linked and involved in bidirectional communication. That interrelationship involves shared usage of common signal molecules and their receptors. The Immune System and its products can modulate neuroendocrine functions and neuroendocrine peptides and hormones can affect important immunological parameters. Specifically, this article review the evidence for immune-neuroendocrine interactions in relation to the Hypothalamic-Pituitary-Adrenocortical axis. Neuroendocrine-immune interactions appears to play an important role in psychosocial influences on immunologically resisted and mediated diseases.

Corticotropin-Releasing Hormone↗