Search PubMed⌕ Search

Biomedical subjects

H Maldonado

Publications and source records attributed to H Maldonado.

At least 37 records · Page 2Linked to original sources
PubMed1996

Serotonin-induced short- and long-term sensitization in the crab Chasmagnathus.

On sudden presentation of a passing shadow (a visual danger stimulus), the crab Chasmagnathus granulatus responds with a running reaction that we term an escape response (ER). A single administration of 5-HT in a dose range between 0.005 and 0.1 microgram/g enhances the ER at 30 min, and a dose of 10-15 micrograms/g has a similar effect for at least 24 h. The classical 5-HT antagonist cyproheptadine (CYP) given within a dose range 0.01-2.0 micrograms/g has no effect on ER at 30 min, but 0.5 microgram/g blocks the 5-HT-induced short-term sensitization. An enhancing effect of CYP on the ER is shown at 24 h with 1.0-2.0 micrograms/g doses. An explanation of this results in terms of a model similar to that proposed for Aplysia, that is two sensitizing processes linked in parallel and mediated by two different types of 5-HT receptors is discussed. Results indicate that the sensitizing effect of 5-HT is confined to high responders, thus suggesting that crabs of a same population have different degrees of sensitivity to the drug according to their different degrees of reactivity to the visual danger stimulus.

Animals↗
PubMed1996

Inhibitors of protein and RNA synthesis block context memory and long-term habituation in the crab Chasmagnathus.

The crab Chasmagnathus granulatus reacts to a shadow passing overhead (a danger stimulus) with an escape response that habituates quickly and for at least 5 days. Recently, it has been reported that cycloheximide (CY) disrupts this long-term habituation and the corresponding context memory. In the present article, experiments with CY and an inhibitor of RNA synthesis, actinomycin-D (ACT), were parallelly conducted. An injection of CY (20 micrograms) or ACT (0.62 microgram) reduced the incorporation of [14C]-aminoacid into cerebral plus thoracic ganglia by 80% for 2 h and 59.7% for 1 h, respectively, but no inhibition was found at 24 h. Both ACT (0.62 microgram) and CY (20 micrograms) administered immediately after training (15 trials with the danger stimulus) impaired either long-term habituation or context memory when tested at 24 h. Because ACT and CY have in common only their direct or indirect inhibitory effect on protein synthesis, this finding is considered as an additional evidence that long-term memory in Chasmagnathus requires de novo protein synthesis. However, pretraining ACT or CY impaired context memory at 24 h but not long-term habituation. Such a disparity is explained by an unspecific attenuating effect upon the response, attributed to drug x training interaction. Neither ACT nor CY affected short-term habituation.

Amino Acids↗
PubMed1996

Acute administration of a permeant analog of cAMP and a phosphodiesterase inhibitor improve long-term habituation in the crab Chasmagnathus.

A shadow passing overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus that habituates promptly and for a long period. Robust retention is shown at 24 h after 15 trials of shadow presentation or at 120 h after 30 trials, but no significant retention is disclosed at 24 h after 5 trials or at 72 h after 15. A cocktail of the cAMP membrane permeable analog 8-(4-chlorophenylthio)-cAMP (CPT-cAMP), plus the phosphodiesterase inhibitor isobutyl methylxanthine (IBMX), was given by systemic administration. Pretraining injection of the cocktail (25 or 50 microM, 15 min before a 5-trial session) failed to affect short-term habituation, but induced significant retention when tested at 24 h. This facilitatory effect was not shown when a lower dose (5 microM) was used. A post-training injection of 25 microM, immediately after a 5- or 15-trial session, induced retention when tested at 24 or 72 h, respectively. Thus, the administration of CPT-cAMP + IBMX during acquisition of a habituated response or immediately after, improves long-term habituation, a result supporting the view that an increase in the cAMP level is one of the steps in long-term memory consolidation.

1-Methyl-3-isobutylxanthine↗
PubMed1996

Angiotensin II enhances long-term memory in the crab Chasmagnathus.

An opaque screen moving overhead provokes an escape response in the crab Chasmagnathus granulatus that habituates after a few presentations of the eliciting stimulus. Fifteen trials with a 180-s intertrial interval or 30 trials with a 90-s interval (strong training protocol) ensures long-term habituation (LTH) of the response for 24 h, whereas 10 trials (weak training protocol) fail to induce it. However, robust LTH is obtained when crabs are injected with human angiotensin (All; 50 pmol) immediately after a weak training protocol. This memory-enhancing effect of All is dose-dependent, reversible by saralasin (5 pmol), and vanishes either when the weak training protocol is reduced to only five trials, or when the peptide is given before training or 1 h after. LTH is impaired by saralasin (5 pmol) administered before or after the strong training protocol, but no amnestic effect is disclosed when the antagonist is given 1 h after. On the other hand, both All-like immunoreactivity and angiotensin-converting enzyme-like activity are described in diverse tissues of Chasmagnathus, namely, in gills and in both thoracic and supraesophageal ganglia. Results support the view that some components of the renin-angiotensin system and their influence on memory might have emerged early in evolution.

Angiotensin II↗
PubMed1995

Acute administration of angiotensin II improves long-term habituation in the crab Chasmagnathus.

A shadow moving overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus granulatus that habituates after 15 trials and for a long period. A shorter training of ten trials fails to induce long-term habituation; however, a good retention of the habituated response is manifest after a 24-h interval when angiotensin II (AII) (10(-6) M, 3 ng/g) is injected post-training. By contrast, no amnestic effect of AII was found even though high doses were administered. The facilitatory effect of AII is suppressed by saralasin (10(-7) M, 0.3 ng/g), a specific angiotensin II receptor antagonist. Results are considered as suggesting that angiotensin on memory processes might have emerged early in evolution.

Angiotensin II↗
PubMed1995

Modulation of the escape response by [D-Ala2]Met-enkephalin in the crab Chasmagnathus.

The synthetic opioid analog [D-Ala2]Met-enkephalin (DAME) significantly reduces the escape response to a danger stimulus in the crab Chasmagnathus granulatus when administered within the dose range 0.01-1.0 micrograms/g. There is no reduction with lower or higher doses, thus suggesting a U-shaped dose-response curve. A 0.1-microgram/g dose of naloxone has no effect per se on the response, but when it is administered together with DAME, it completely blocks the decremental effect of this drug and an escape response generally higher than that of control is observed. An explanation for these results in terms of a possible dual action of DAME is offered. In addition, we present evidence for different degrees of opiate sensitivity among crabs of the same population in relation to their different degrees of reactivity to the visual danger stimulus.

Animals↗
PubMed1995

Cycloheximide inhibits context memory and long-term habituation in the crab Chasmagnathus.

A shadow moving over head elicits an escape response in the crab Chasmagnathus that habituates promptly and for a long period. The effect of the protein synthesis inhibitor cycloheximide (CY) on this long-term memory was analyzed. Two hours after injection, 10 micrograms CY inhibited [14C]-amino amino acid incorporation into cerebral plus thoracic ganglia by 88% and 20 micrograms by 92%, but no inhibition was found at 24 h. A single injection of 10-20 micrograms CY given 30 min before training, failed to affect the short-term habituation. Similar doses impaired both context memory (CM) and long-term habituation (LTH) when tested at 72 and 120 h but only CM at 24 h. Such a disparity was explained by an unspecific depressing effect upon the response, attributed to an interaction between CY and training. The hypothesis was confirmed, because CY injected immediately after training disclosed amnestic effect at 24 h on both CM and LTH. A similar effect was proven when animals were injected at 2 h but not at 6 h after training. Results from experiments with pretraining and pretesting injections put aside a state-dependence or retrieval deficit effects of the drug. Taken together, findings of this article argue strongly for de novo protein synthesis as a mechanism of LTH and for the close relation between CM and LTH.

Amino Acids↗
PubMed1994

Octreotide therapy of large-volume refractory AIDS-associated diarrhea: a randomized controlled trial.

OBJECTIVE: To compare the effect of octreotide (a long-acting somatostatin analog) to that of antidiarrheal therapy plus placebo on large-volume refractory AIDS-associated diarrhea. DESIGN: A randomized controlled trial. SETTING: Referral-based clinic and hospital in a tertiary care center. PATIENTS: Twenty male patients with AIDS and refractory diarrhea, with stool volume > 1000 ml/day who failed to improve after initial supportive management. All patients finished the study. INTERVENTIONS: Patients were randomly given either octreotide in doses of 100, 200 and 300 micrograms subcutaneously every 8 h, or high doses of loperamide and diphenoxylate orally plus placebo subcutaneously for 10 days. MAIN OUTCOME MEASURES: Bowel movements and stool volume were registered before and every day after treatment by the patients themselves and the nursing personnel. RESULTS: Patients from both groups were similar for age, time of AIDS diagnosis, duration of diarrhea and etiology. Baseline mean bowel movements per day (9.4 +/- 2.8 in the octreotide group versus 10 +/- 3.1 in controls) and baseline mean stool volume (2753 +/- 840 versus 2630 +/- 630 ml/day, respectively) were similar in both groups before therapy (P < 0.05). Mean bowel movements per day after 10 days of therapy was 2.1 +/- 1.6 in the octreotide group versus 7 +/- 3 in controls (P < 0.05). Mean stool volume after 10 days of therapy was 485 +/- 480 in the octreotide group versus 1080 +/- 420 ml/day in controls (P < 0.05). Complete response (stool volume < 250 ml/day) was observed in two patients from the octreotide group and none from controls; partial response (decrease > 50% in stool volume) in four and two; and no response (decrease < 50% or no change) in four and eight (P < 0.05), respectively. Side-effects occurred in eight out of 10 octreotide patients and three out of 10 controls (P < 0.05), but none were significant to result in discontinuation of medication. CONCLUSION: Octreotide proved to be superior to conventional therapy in this short-term treatment of large-volume refractory AIDS-associated diarrhea.

Acquired Immunodeficiency Syndrome↗
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↗