Stimulus generalization of conditioned taste aversion in rats

Relatively little information is available regarding the intradimensional stimulus generalization of conditioned taste aversion (CTA). Experiment 1 employed a between-groups generalization test to examine the extent to which conditioned flavor aversion to one sucrose solution generalized to other concentrations of sucrose in adult rats. Evidence of a gradient of aversion was obtained. Because generalization gradients in other tasks have been found to flatten over a retention interval, Experiment 2 investigated the effects of delayed testing (2, 7, or 21 days) upon the slope of the generalization gradient. The generalization gradient flattened at the intervals, suggesting that subjects forgot the specific attributes of the conditioning concentration and avoided generalized stimuli as if they were the original CS. Experiment 3 used a long delay between taste and toxicosis to degrade the associative contingency and found no evidence that the generalization gradients found in the first two experiments could be explained in terms of enhanced neophobia due to poisoning. These findings provide further evidence (cf. A. W. Logue, 1979, Psychological Bulletin, 86, 276-296; M. Domjan, 1980, in J. S. Rosenblatt, R. A. Hinde, C. Beer, & M. Busnel (Eds.), Advances in the study of behavior, Vol. 11, New York: Academic Press) that CTA shares a number of similarities with other learning processes. Further, they illustrate that stimulus forgetting can be detected in a paradigm considered relatively immune to retention loss.

Alleviation of infantile amnesia in rats by means of a pharmacological contextual state

Although a number of studies have demonstrated that the relatively rapid rate of forgetting in young rats (i.e., infantile amnesia) can be alleviated by various reminder treatments, the possibility of enhancing retention by other procedures seems largely unexplored. Given the putative importance of contextual cues as sources of memory retrieval, this experiment examined whether the presence of a distinctive pharmacological state at training and testing could override infantile amnesia. Weanling rats were given pentobarbital or saline prior to Pavlovian fear-conditioning. When tested 1 week later, subjects in the same-state drug condition showed better retention than the same-state saline group. This finding extends previous work on memory recovery in young animals by demonstrating alleviation of infantile amnesia without a re-exposure to the CS or UCS during the retention interval.

Is anterograde amnesia a special case of retrograde amnesia?

In anterograde amnesia, memory loss is obtained for events that occur subsequent to the traumatic insult. But because the effects of an anterograde agent or treatment usually last for minutes, or even hours, after the nominal training event, processing of information may be altered during the postacquisition period as well as during acquisition. Since posttraining manipulations are themselves capable of modulating memory, or inducing retrograde amnesia, the memory loss due to a putative anterograde treatment may instead represent retrograde processes. The present experiment examined this potential source of confounding by using an amnestic treatment that can be quickly reversed after training in order to remove postacquisition effects. Thus, the presence of amnesia would isolate anterograde contributions as the source of loss. For induction of anterograde amnesia, rats were trained while at reduced body temperature (29 degrees C). A rapid rewarming procedure was introduced for some animals immediately after training to ensure that the hypothermic state did not extend into the postacquisition period. Other subjects were rapidly rewarmed 1 hr after training to control for any effects of the rewarming manipulation. Both groups showed severe anterograde amnesia that was indistinguishable from that obtained in the gradually rewarmed controls. These data provide an empirical example of an anterograde-induced memory deficit that is independent of retrograde influences.

Persistence of flavor neophobia as an indicator of state-dependent retention induced by pentobarbital, stress, and estrus

As fear conditioning paradigms have failed to find state-dependent retention (SDR) in rats dissociated by the estrous state, an attempt was made to establish a paradigm involving the attenuation of flavor neophobia as a more sensitive indicator of SDR. Experiment 1 established that the paradigm did indicate SDR in male rats dissociated by pentobarbital (10 mg/kg). Experiment 2 generalized the utility of the technique by employing an endogenous state, shock-induced stress, as the dissociative state. Having proved to be an indicator of SDR in the first two experiments, the technique was used in Experiment 3 to investigate the possible dissociative characteristics of the estrous state in female rats. Estrus was investigated because, due to the hormonal condition during estrus, it may provide a useful tool in investigating the dissociative aspects of human perimenstrual periodic psychosis. In Experiment 3, using ovariectomized female rats brought into estrus by injection of estrogen and progesterone in a sequence and amount comparable to the natural cycle, estrus was not demonstrated to be dissociative, i.e., did not produce SDR. The implications of these results in relation to perimenstrual periodic psychosis were discussed.

Anterograde memory loss induced by hypothermia in rats

In contrast with the extensive animal research on retrograde amnesia, relatively little attention has been given to anterograde amnesia. Moreover, previous studies of anterograde amnesia have not always clearly separated the effects of the anterograde treatment on acquisition from those on retention. Thus, hypothermia-induced anterograde amnesia for a one-trial conditioned fear memory was examined in three experiments. Experiment 1A demonstrated an anterograde disruption of performance in subjects receiving training in the hypothermic state (29 degrees C) and tested 24 hr later. Acquisition of the target memory in animals exposed to hypothermia prior to conditioning was demonstrated in Experiment 1B. Subjects conditioned while in a hypothermic state (29 degrees C) performed similarly to noncooled subjects if tested shortly after conditioning (while still in a hypothermic state), but not 24 hr after conditioning (while in a normothermic state). Experiment 2 shows that the anterograde amnesia effect is temperature dependent. That is, of animals trained at 29 or 33 degrees C, only the more hypothermic group demonstrated deficits in retention when tested 24 hr later. This experiment also attempted, unsuccessfully, to demonstrate recovery of the amnestic memory by administration of a noncontingent footshock prior to testing. Implications of the failure to demonstrate recovery of memory are discussed along with possible mechanisms involved in producing anterograde amnesia.

Automated nitrogen-washout methods for infants: evaluated using cats and a mechanical lung

Infants with respiratory distress syndrome are treated with constant distending pressures to counter atelectasis and increase the functional residual capacity (FRC). However, FRCs are not monitored in these severely ill infants because present methods are impractical. We computerized N2-washout techniques for estimating the lung volume in these infants. The system has been evaluated using 1) a mechanical lung model and 2) small cats with normal and edematous lungs. Comparing the results of measured lung volumes with the fixed mechanical lung volumes yielded a correlation coefficient 0.996 (n=50). Decreasing the N2 gradient between initial N2 concentration and the washout medium from 0.79 to 0.10 did not affect the accuracy or reproducibility of measurements in the mechanical lung. For normal cats, comparing the results of N2-washout measurements of FRC with He-dilution values yielded a correlation coefficient of 0.921 (n=128); results from cats with pulmonary edema yielded a correlation coefficient 0.989 (n=80). We conclude that this computerized system is accurate, reproducible, and clinically acceptable for monitoring infants.

Onchocerciasis diagnosis and the probability of visual loss in patients with skin snips negative for Onchocerca volvulus microfilariae

Two methods have been used to verify the diagnosis of patients living in the onchocerciasis hyperendemic region of Liberia found to have O.v. negative skin snips. The first was based on a histological and an electronmicroscopic examination of the skin to determine whether the characteristic onchocerciasis dermatitis was absent, and to compare the results with age matched subjects having minimal to densely O.v. mf infested skin. The second method involved the skin response of patients with O.v. mf negative skin snips to topically applied DEC. No O.v. mf were found in skin snips serially sectioned and examined histologically from patients in which the results of incubation studies were completely negative. Skin snips from these seemingly O.v. mf negative patients had a dermatitis, whereas no dermatitis was found in skin snips taken from subjects living in nearby nonendemic areas. Patients with O.v. mf positive skin snips responded to DEC applied topically with increased pruritus and a papular rash whose severity was proportionate to the intensity of infestation. Patients with O.v. mf negative skin snips responded to DEC applied topically with increased pruritus and developed either a localized papular rash or widely dispersed papules; confirmation of onchocerciasis in these patients was found in the identification of O.v. mf in histological sections of the papules.

Generalization of reading by special education students from a structured program to informal classroom activities

15 special education students exhibited an increase in the number of correctly completed frames in the Sullivan Programmed Reading Series following introduction of a reinforcement contingency. The mean number of frames remained high during the reversal phase with no consistent generalization of effects from the morning reading program to an afternoon free-time period.

Kinetics of Mg2+ flux into rat liver mitochondria

Unidirectional fluxes of Mg2+ across the limiting membranes of rat liver mitochondria have been measured in the presence of the respiratory substrate succinate by means of the radioisotope 28Mg. Rates of both influx and efflux of Mg2+ are decreased when respiration is inhibited. A linear dependence of the reciprocal of the Mg2+ influx rate on the reciprocal of the Mg2+ concentration is observed. The apparent Km for Mg2+ averages about 0.7 mM. N-Ethyl-maleimide, an inhibitor of transmembrane phosphate-hydroxyl exchanges, enhances the observed pH dependence of Mg2+, influx. In the presence of MalNEt, the apparent Vmax of Mg2+ influx is greater at pH 8 than at pH 7, and there is a linear dependence of the Mg2+ influx rate on the external OH- concentration. The K+ analogue Tl+ inhibits Mg2+ influx, while La3+, an inhibitor of mitochondrial Ca2+ transport, has no effect on Mg2+ influx. Mg2+ competitively inhibits the flux of K+ into rat liver mitochondria. The mechanism(s) mediating mitochondrial Mg2+ and K+ fluxes appear to be similar in their energy dependence, pH dependence, sensitivity to Tl+, and insensitivity to La3+.

A transepidermal chemotherapy of onchocerciasis

Counts of microfilariae in the skin, and histological and electronmicroscopic procedures have been used to analyze the response of onchocerciasis patients to diethylcarbamazine citrate (DEC) given either orally or topically. Oral administration of DRC failed to eliminate all microfilariae. Transepidermal DEC resulted in rapid degeneration of microfilariae, and daily single applications of the drug greatly reduced or apparently eliminated microfilariae from the skin. Following weekly topical applications of a DEC emulsion, effective suppression of O. volvulus microfilariae in patients living in a hyperendemic area was maintained for many months; and the dermal pathology resolved.

Gastric bezoar formation secondary to gastroparesis diabeticorum

Diabetic autonomic neuropathy may result in delayed gastric emptying and gastric retention. A case of gastric phytobezoar formation that was secondary to diabetic autonomic neuropathy is reported. Greatly impaired gastric emptying was documented in this case by administration of a radiolabelled meal. Parenteral metoclopramide hydrochloride completely corrected the patient's gastric motility disturbance.

Unpredictability of theophylline saliva measurements in chronic obstructive pulmonary disease

The use of saliva as an indirect, non-invasive method of theophylline plasma level measurement was evaluated in 23 older men with chronic obstructive pulmonary disease and numerous concurrent medical problems. Simultaneously collected plasma and saliva samples were obtained on two or more occasions and analyzed for theophylline concentration by the Schack and Waxler spectrophotometric method. The mean (+/- SD) plasma:saliva ratio for 84 sample sets was 1.6 (+/- 0.5) with the saliva concentration averaging 64.8% (+/- 20.8%) of the plasma concentration. Multiplying a randomly chosen plasma:saliva ratio from each patient by the saliva concentration of a second randomly selected observation resulted in a predicted plasma concentration that differed by more than 20% of the measured concentrations for 16 of the 23 patients. Thus, use of saliva theophylline measurements obtained by the Schack and Waxler method to adjust dosage regimens cannot be recommended in these patients.

Effects of a modified DRL schedule with special education students

The purpose was to document the effects of a modified DRL (differential reinforcement of low response rates) schedule of reinforcement with a class of 17 elementary students in special education. The procedure permitted students access to reinforcers if they exhibited 5 or fewer rule violations in a 90-min. period. Monitored target responses were out-of-seat and talking-out behaviors. The results indicated a low mean number of responses per student when the experimental program was in operation and a substantial increase in mean number of responses per student when the experimental program was withdrawn.

Myocardial uptake (rabbit) of six 99mTc-tagged pharmaceuticals and 85Sr after vasopressin-induced necrosis

A new rapid method for producing myocardial necrosis in rabbits was developed, using percutaneous intramyocardial injection of vasopressin in peanut oil. The 15-min procedure resulted in a mortality rate of 15% and a success rate among surviving animals of 50%. When the lesions were 24 hr old, strontium-85 and a technetium-99m-tagged agent were injected intravenously simultaneously, and the animals were killed 1,6, and 24 hr later for tissue radioassay. Strontium-85 failed to accumulate appreciably in the lesions. Three bone-seeking technetium complexes (pyrophosphate, methylene diphosphonate, and imidodiphosphonate) produced lesion-to-normal myocardial ratios of 6,5, and 14, respectively, at 1 hr, and 20,30, and 33 at 6 hr. The ratios for 99mTc-glucoheptonate were only 2 at 1 hr and 4 at 6 hr, while the ratios of 99mTc-acetylcysteine and 99mTc-citrate were even lower.

Propranolol and morphine

The morphine blocking and anticonvulsant effects of propranolol were investigated in mice. Three different convulsant procedures (electroshock, pentylenetetrazol and thebaine) were used. In addition, LD50's of morphine after different doses of propranolol were done. Sotalol was used as a control drug to check which of the effects of propranolol could be regarded as due to beta blockade. Morphine LD50 in mice is not altered by pre-treatment with propranolol. The anticonvulsant characteristics of propranolol are different from those of sotalol, the former acting mainly on the tonic phase of the seizures. This study does not support the hypothesis that propranolol is a morphine antagonist but reinforces the idea that propranolol has definite central nervous system effects.

Acute hemorrhagic cerebellar infarction following angiography

Cerebellar infarction following cerebral angiography is an unusual complication. A case is reported. The patient's condition deteriorated with each diagnostic study. Improvement occurred after cerebellar decompression and evacuation of an intracerebellar hematoma.