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Biomedical subjects

H Maldonado

Publications and source records attributed to H Maldonado.

At least 19 recordsLinked to original sources
PubMed1992

Conditioned facilitatory modulation of the response to an aversive stimulus in the crab Chasmagnathus.

A mild electrical shock delivered to the walking legs of the crab Chasmagnathus granulatus through a fine layer of sea water, induces a running response that declines after repeated stimulation. Herein, a first series of experiments was aimed at conditioning the response to a light or a dark pulse, but no detectable CR was disclosed during training nor in a later test with the CS alone, even though several stimulus parameters were assayed. In a second series, crabs were repeatedly exposed during training to a light pulse (CS) immediately followed by shock (UCS), and after a 6-h rest interval, tested with either CS-UCS or UCS. The CS-UCS presentation at testing elicited a higher recovery (potentiated recovery, circa 70%) than that evoked by the UCS alone (unconditioned recovery, circa 35%) (Experiment 3). An experiment including the explicitly unpaired control procedure (Experiment 4), confirmed that the enhanced response (CR) to the shock (UCS) (measured as potentiated recovery) is conditioned to an illumination signal (CS). An alternative explanation of the potentiated recovery in terms of retardation of habituation proved hardly tenable (Experiment 5). In Experiment 6, crabs were exposed to a variety of light pulse shock and dark pulse shock temporal relationships, and results were found consistent with a delay of reinforcement gradient when light termination was considered as CS. Thus a decrease in luminance is able to become associated with shock and to condition an enhanced response regardless of light termination being the offset of a light pulse or the onset of a dark pulse.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Opiate effect on the threat display in the crab Carcinus mediterraneus.

The well-known defense response of a crab (laterus merus display, LMD) was easily evoked in Carcinus mediterraneus by striking the cephalothoraxic protogastric region between the eyestalks. Following a program aimed at investigating the regulatory action of diverse neuromodulators on the LMD of this crab, a study on the role of opioids was started by testing the effect of morphine administration. Injection of morphine HC1 (MP) (40, 50, 60, 70, or 100 micrograms/g) produced a dose-dependent reduction of the LMD so elicited that dissipated with the postinjection time. Only MP doses higher than 50 micrograms/g were effective 30 min after drug administration. The MP-induced inhibition of LMD was blocked by a 4.8-micrograms naloxone HC1/g dose injected 10 min before MP. These results and those previously obtained as the action of GABA on the LMD of this crab are discussed in connection with results reporting a similar effect of these drugs on another agonistic item of behavior in the crab Chasmagnatus granulatus. The possibility of demonstrating habituation of the LMD to an iterated stimulation in C. mediterraneus and of using such a process to elucidate the acting paths of the drugs is discussed.

Aggression↗
PubMed1992

Multitrial inhibitory avoidance learning in the crab Chasmagnathus.

Chasmagnathus crabs placed in the dark compartment (DC) of a double-chamber device and given electrical shocks whenever they entered or remained in the light compartment (LC), showed an LC-avoidance behavior when tested 24 h after a training session of three 30-min periods with 60-min intervals. The avoidance behavior depended neither on the shock number nor on the distribution at training but only on exposure to the LC-shock contingency, thus suggesting that crabs learn to associate the LC with an aversive situation. The learning outcome disclosed a higher degree of refraining from entering the LC rather than a faster escaping to the DC. Distributed practice proved more effective on crab avoidance learning than massive practice. Retention of the learned behavior occurred after a 24-h rest interval in an environment different from that of the training apparatus. Experimental devices previously used in avoidance learning studies with crabs were improved here by automating both the computation of latency values and the event recording.

Animals↗
PubMed1992

Cell volume and pH regulation by the Amphiuma red blood cell: a model for hypoxia-induced cell injury.

The Amphiuma red blood cell is one of the model systems employed early in the study of vertebrate cell volume regulation. Following both cell swelling and shrinkage the Amphiuma red blood cell demonstrates volume regulation to virtual completion in 90-120 min. When swollen the Amphiuma red blood cell loses K, Cl and osmotically obliged water, while following shrinkage volume regulation is the result of Na, Cl and therefore water uptake. The main contribution of the Amphiuma red cell as a model is that it was the first cell in which volume regulation was demonstrated to be electroneutral and more specifically that K/H and Na/H exchangers were responsible for regulation following cell swelling and shrinkage, respectively. Additionally, the Amphiuma red blood cell K/H and Na/H exchangers have been demonstrated to function in a pH regulatory capacity. The latter observation in turn led to the demonstration of the mutually exclusive and contradictory nature of volume and pH regulation predicted upon Na/H exchanger activity. These observations prompted our recent investigations of the Na/H exchanger as a contributor to hypoxia-induced cell damage, using the rabbit heart as a model. These studies illustrated that Na, and Ca imbalances characteristic of hypoxia-induced cell damage are ultimately referable to the Na/H exchanger's function in a pH regulatory capacity, which contributes fundamentally to cell volume and Ca derangement and ultimately cell injury.

Animals↗
PubMed1992

Variations of magnesium, iron, copper and zinc during the colonic wound healing process: experimental study on rabbits.

The role of trace elements in the wound-healing process is still controversial. Their variations within a normal colonic wound healing have never been studied. An experimental study on rabbits was designed to study magnesium, iron, copper and zinc variations in blood, normal colonic walls and colonic anastomoses on each of the first 7 postoperative days. No major variations of Mg could be observed. Fe decreased in blood as well as in colonic walls and anastomoses. Cu increased in blood, whereas it decreased in colonic walls and anastomoses. Zn decreased in blood, whereas it increased in colonic walls without significant changes in anastomoses. The role of Fe seemed to be rather difficult to understand. Plasma mobilization seems to explain the local use of Zn, while early tissue release with further return in blood occurred for Cu. The importance of a well-balanced nutritional status is underlined to prevent and correct the variations of trace elements in the postoperative course.

Anastomosis, Surgical↗
PubMed1991

Habituation and sensitization to an electrical shock in the crab Chasmagnathus. Effect of background illumination.

The escape response of the crab Chasmagnathus granulatus, elicited by an electrical leg-shock, wanes as a consequence of repeated stimulation, and the decrease persists after a 24-h rest interval. Results concerning stimulus specificity in within- and between-sessions habituation strongly indicate that neither motor fatigue nor sensory adaptation nor damage can account for the response waning, which thus meets the major criteria of habituation. A comparison between the escape response habituation to leg-shock and that to a shadow passing overhead discloses clearcut differences. The shock curve shows an initial hump positively related to stimulus intensity, suggesting that a shock-induced sensitization along with habituation subserves the response curve. The curve asymptote is remarkably high and, unlike the initial waning portion, not greatly affected by treatment changes, hinting that the response may be the combination of an escape response and a basal one (an undirected burst of activity). The waning portion is higher when shocks are given in dark than when given in light, but this effect is not considered as an extra eliciting-stimulus-induced sensitization, since the reactivity enhancement depends necessarily on the darkness-shock concomitance, regardless of prior exposure to darkness. Accordingly, the hypothesis that crab habituates not only to a shock but to a complex stimulus (shock + background illumination) is put forward and discussed.

Animals↗
PubMed1991

Morphine and GABA: effects on perception, escape response and long-term habituation to a danger stimulus in the crab Chasmagnathus.

Prior results (37) showed that morphine pretreatment reduces the escape response of the crab Chasmagnathus to a shadow passing overhead and prevents the acquisition of a long-term habituation. These results were explained by a reduction in the danger signalled by the stimulus, and to test this hypothesis methods other than morphine injection were used herein to abolish response during training. GABA pretreatment induced a dose-dependent reduction in responsiveness to the danger stimulus, and instances of autotomy were shown with doses larger than 12 micrograms/g. A response was rarely displayed with a 9 micrograms GABA/g dose given 5 min before training, but long-term memory was acquired. In one experiment, both morphine and GABA pretreatment produced similar mild response inhibition during training, but morphine, not GABA impaired long-term habituation. Morphine administered immediately after training had no amnesic effect. These results support the hypothesis that morphine effects may be explained by transient disruption between the stimulus and its danger meaning, ruling out alternative explanations such as response inhibition or amnesia due to either storage or retrieval failure.

Animals↗
PubMed1991

Nonhabituation processes affect stimulus specificity of response habituation in the crab Chasmagnathus granulatus.

The escape response of the crab (Chasmagnathus granulatus) habituates to repeated electrical shock (SH) or to the presentation of a screen moving horizontally (H) or vertically (V) overhead. Stimulus specificity of the habituated response is shown 24 hr after training but not after either 90 or 45 min. This disruption at short intervals is explained by a transient effect that arises from training: SH training and H training attenuate and V training enhances reactivity. The attenuating effect of H training is reduced by naloxone when administered before but not after training. The results support the hypothesis that during the crab's training two types of processes takes place: a stimulus-specific, long-lasting habituation process that promotes between-sessions response habituation and a nonhabituation process that promotes nonstimulus-specific, less persistent changes of behavior that involve either response habituation or response sensitization. The effect of H training seems to be mediated by an opioid mechanism through secondary activation.

Animals↗
PubMed1990

Long-term habituation to a danger stimulus in the crab Chasmagnathus granulatus.

A shadow moving overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus granulatus, that habituates after 15 stimulus presentations at 3-min intervals. Here, the habituation was induced by 3 diverse shadow stimuli and the habituated response persisted after 24 hr in every case. This long-lasting effect failed to appear if the testing stimulus did not keep the same spatial specificity as that of the training one. A partial stimulus generalization was detected, when training and testing stimuli differed in size. The adaptive value of a high danger stimulus specificity in long-term habituation is discussed. Extinction of the long-term habituated response failed to occur although crabs were exposed to the context in the absence of danger stimulation.

Animals↗
PubMed1990

Central effect of morphine pretreatment on short- and long-term habituation to a danger stimulus in the crab Chasmagnathus.

Morphine is believed to inhibit the crab's escape response to a danger stimulus due to central drug action. To test alternative explanations of such an effect in terms of afferent and/or efferent impairment, experiments were conducted using the crab's optokinetic response as indicator. Doses of morphine with maximal detrimental effect on the escape response (75-100 micrograms/g) showed no effect on the optokinetic response, both by measuring the crab's eyestalk displacement and by recording its body rotation, supporting the hypothesis of a morphine central action on the danger-induced escape response. As regards the effect on habituation, a 75 micrograms morphine/g injection administered 30 min before the first trial produced a parallel shift of the short-term (within-session) habituation curve, suggesting a modulatory central drug action that would mimic a putative endogenous opioid action. A 100 morphine micrograms/g dose injected 30 min before training sharply reduced reactivity during training and impaired the acquisition of long-term (between-session) habituation. It may be speculated that the decrease in the danger meaning of the stimulus due to morphine explains both effects in terms of a stimulation impairment during training.

Animals↗
PubMed1990

Effect of naloxone pretreatment on habituation in the crab Chasmagnathus granulatus.

On sudden presentation of a passing shadow, the crab Chasmagnathus granulatus reacts with an escape response that habituates after repeating the same stimulus. In a first series of experiments, a range of naloxone (NX) doses (0.8, 2.4, 3.2, and 6.2 micrograms/g) was injected into crabs 15 min before one 15-trial habituation session. An enhancing effect of 3.2 micrograms NX/g on responsiveness appeared over trials, that cannot be explained either by a ceiling effect or by a delay in peak drug action. Two doses below 3.2 microgram/g and one dose above had no significant effect. Results from a second series of experiments showed that the 3.2 microgram NX/g effect vanishes after 15 trials (1 h after injection). The hypothesis that crab's habituation involves the action of an endogenous opioid mechanism is put forward to account for the naloxone pretreatment effect.

Animals↗
PubMed1990

Multidisciplinary analysis of patients with extratemporal complex partial seizures. II. Predictive value of semiology.

Eight patients were diagnosed as having extratemporal seizures based on their ictal electroclinical manifestations. The correlation between the focus based on semiology and that based on intracranial electrographic recording and surgical excision was excellent in five, good in three. The electroclinical manifestations of seizures are important data to consider in the diagnosis and treatment of extratemporal seizure foci.

Electroencephalography↗
PubMed1990

Retrograde amnesia in praying mantis after two successive learning processes.

Learning and memory consolidation was investigated in the mantis Stagmatoptera biocellata, by two successive trainings: a) the attack (A) avoidance training in which animals were not allowed to catch a mobile star, followed by the deimatic reaction (DR) avoidance training of not displaying this defensive response, or b) DR-avoidance training followed by A-avoidance training. The results showed that the presence and the 1 of A-avoidance learning and DR-avoidance learning did not affect the learning of the other training. Total retention of A-avoidance memory was demonstrated when A-avoidance training was given first, whereas DR-avoidance memory was significantly lost (716%) when the DR-avoidance training was given first. The retroactive forgetting of DR-avoidance memory is considered as retrograde amnesia rather than retroactive memory inhibition because it depends on the activity during A-avoidance training (number of attacks) and not the quantity of A-avoidance learning. The magnitude of the amnesic effect due to this distracting activity in the A-avoidance training appears to be remarkably similar to that reported in a previous work using nitrogen-induced anoxia as the amnesic factor.

Animals↗
PubMed1990

[Improvement in the healing of colonic anastomoses by vitamin B5 and C supplements. Experimental study in the rabbit].

To study the effects of vitamins B5 and C on the healing process of colonic anastomoses, 3 groups of 20 rabbits were given daily either placebo (group A), or vitamin B5 (100 mg/kg: group B) or vitamin C (100 mg/kg: group C). After 8 days of supplementation, via a midline incision and under general anaesthesia, 2 colonic segments were removed, and the continuity was restored. On the 3rd post-operative day, the rabbits were killed and the anastomoses were removed. Mechanical properties of both normal colon and anastomoses were determined by using bursting pressure tests, number of burst anastomoses, fibroblast count, hydroxyproline concentration and determination by microanalysis of trace element content: Mg, P, S, Ca, Fe, Cu, Zn and Mn. Vitamin B5 (p = 0.03) and vitamin C (p less than 0.01) both decreased the number of burst anastomoses. Furthermore the required bursting pressure values were higher with vitamin C (p = 0.01) than in controls. Both vitamins restored normal Zn levels at the anastomotic site, whereas these levels decreased on the 3rd post-operative day during the normal healing process of colonic anastomosis. Moreover, vitamins B5 and C increased Fe, Cu and Mn levels, which are intimately all involved in collagen synthesis. Vitamins B5 and C enhance the colonic wound healing process in the rabbit, acting together in synergy in vivo as well as in vitro, as previously demonstrated.

Anastomosis, Surgical↗
PubMed1990

[Brunn's nests as a cause of benign tumor of the bladder in children].

This report concerns the case of a male patient admitted for an operation due to vesicoureteral reflux. During the operation a sessile tumor was discovered in the interior of the bladder at the level of the neck. The tumor corresponded histologically to a mucous polyp with Brunn's nests in the interior. The following are commented on: the extreme rarity of the case, the histopathological characteristics of this abnormal epithelial proliferation which is produced as an exaggerated response to an irritative stimulus and its non-malignant nature.

Epithelium↗
PubMed1989

Danger stimulus-induced analgesia in the crab Chasmagnathus granulatus.

When a danger stimulus (a passing shadow) is presented to the crab Chasmagnathus granulatus, an escape response is elicited that habituates after repeated stimulation. Results from previous work suggest that this habituation might be mediated by endogenous opiates and, thus, that after an habituation session an analgesic effect on the response to a painful stimulus should be found. The purpose here was to test this contention. Each crab was lodged in an actometer where two 2-trial sessions with electrical shock stimulation were given (SS1, SS2), the intersession interval being 60 or 105 min, and the response activity recorded. In some experiments, repeated shadow stimulation was inserted during the interval, and the response activity also recorded. In Expt. 1, shadow sessions of 15 and 30 trials were tested and a significant decrease of the reactivity to the shock was only shown with 30 trials. In Expt. 2, crabs were immediately injected after SS1 with distilled water (d.w.) or naloxone (NX) (3.2 micrograms/g), and a shadow session of 30 trials was given to half of the d.w. animals and to half of the NX ones. NX injected crabs showed an increased responsiveness to the danger stimulus during the shadow session but no inhibitory effect on pain reactivity to the subsequent painful stimulus. Issues concerning dependence of the analgesia on danger stimulus iteration and on stimulus controllability, as well as the opioid nature of the analgesia, are discussed.

Analgesia↗
PubMed1989

Opioid action on response level to a danger stimulus in the crab (Chasmagnathus granulatus).

When a passing shadow is presented to the crab (Chasmagnathus granulatus), an escape response is elicited that habituates after repeated stimulation. Results of previous papers suggest that this habituation might be mediated by endogenous opiates, entailing the postulate that opiates may inhibit the response to a danger stimulus. This contention is tested herein. Two trials (T1, T2) of shadow stimulation were given 30 min apart, and the response activity was recorded. In Experiment 1 a range of morphine doses (0, 25, 50, 75, and 100 micrograms/g) were injected into crabs immediately after T1. Analysis of the M response values showed a morphine dose-dependent reduction in the crab's reactivity to the danger stimulus in T2. In Experiment 2, groups of crabs were injected with 1 of 4 solutions; saline, 70 micrograms/g morphine, 70 micrograms/g morphine plus 1.6 micrograms/g naloxone. Results suggest that morphine acts through an opiate receptor to inhibit the crab's response level to a danger stimulus. Three possible mechanisms of the morphine effect are discussed, and the most viable one suggests a central site of action.

Animals↗