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PubMed1990

Characterization of the cognitive effects of combined muscarinic and nicotinic blockade.

Choice accuracy performance in the radial-arm maze is dependent upon the integrity of both the nicotinic and muscarinic cholinergic receptors. Pharmacological blockade of either of these subtypes of cholinergic receptors with mecamylamine or scopolamine impairs choice accuracy in the radial-arm maze. We have previously demonstrated that the performance deficit caused by muscarinic blockade is exacerbated in at least an additive fashion by coadministration of the nicotinic antagonist, mecamylamine. In the present study, it was found that mecamylamine and scopolamine act together in a greater than additive fashion in disrupting radial-arm maze choice accuracy. When doses of these drugs which do not by themselves cause significant impairments in choice accuracy are given together, they induce a pronounced impairment. Previous results have shown that the adverse effects of nicotinic blockade could be reversed by the dopaminergic D2 agonist LY 171555. In this study, this drug was found to attenuate the cognitive impairment caused by combined nicotinic and muscarinic blockade. On the other hand, the dopaminergic D1 antagonist SCH 23390 which has previously been shown to reverse the adverse effects of muscarinic blockade was not found in this study to attenuate the impairment of combined nicotinic and muscarinic blockade. Since combined nicotinic and muscarinic blockade approximates generalized cholinergic underactivation, treatments like LY 171555, which attenuate the adverse effects of this combined blockade, may be useful in treating syndromes like Alzheimer's disease, which are characterized by generalized cholinergic loss.

Animals↗
PubMed1990

Cholinergic receptor antagonists impair formation of intermediate-term memory in the chick.

Several experiments examined the effects of cholinergic receptor antagonists on formation of memory in the chick. Scopolamine produced amnesia in chicks trained on a one-trial peck avoidance task in a dose-dependent manner. Pretraining injection of scopolamine produced amnesia that developed between 15 and 30 min after training, suggesting that scopolamine interferes with intermediate-term memory (ITM), previously described to be active during this time (Patterson, Alvarado, Warner, Bennett, & Rosenzweig, 1986). Pretraining injection of scopolamine or ouabain, an inhibitor of ATPase activity shown previously to inhibit formation of ITM, produced identical time courses of amnesia development, supporting the hypothesis that scopolamine interferes with ITM. Pirenzepine, an inhibitor of M1 muscarinic receptors, was effective in producing amnesia, whereas gallamine, an M2 receptor inhibitor, did not produce amnesia. These results suggest that M1, but not M2, receptors are involved in memory formation in the chick.

Animals↗
PubMed1990

Rats with dorsal hippocampal lesions do react to new stimuli but not to spatial changes of known stimuli.

The effect of visual distracting stimuli upon the straight alleyway performance of dorsal hippocampectomized Wistar rats was investigated. In comparison with control animals it was observed that dorsal hippocampectomized animals (1) ambulated more during the preexposure phase, (2) acquired at the same rate a running response for food (training phase), (3) reacted similarly to a new visual stimulus (black cards) presented in a sector of the alleyway, and (4) habituated to successive presentations of that stimulus in the same place. (5) However, dorsal hippocampectomized rats did not react, unlike the controls, to the presentation of the same stimulus in another place of the alleyway but (6) reacted to the visual pattern change of the stimulus (now black/white check cards) in the same place. These results indicate that under certain experimental conditions, hippocampus-lesioned animals are capable of interrupting a running response for food in order to explore a new conspicuously located stimulus, habituate to repeated presentations of that stimulus, and to react to a new pattern of visual stimulation. They suggest that hippocampectomized rats do not lose the capacity to react to a new stimulus; the disruption seems to be related to the spatial context of stimulus presentation, supporting a spatial mapping hypothesis of hippocampal function.

Animals↗
PubMed1991

Comparison of the effects of scopolamine administered before and after acquisition in a test of visual recognition memory in monkeys.

The effect of scopolamine on visual recognition memory in rhesus monkeys was assessed with a delayed nonmatching-to-sample task employing trial-unique stimuli. During the acquisition phase, 40 sample stimuli were presented sequentially. During the test phase, these same stimuli were presented in the reverse order, each paired with a novel stimulus. The animal was rewarded for choosing the novel stimulus in each pair. Two versions of this design were used. In Task 1, scopolamine (10.0 or 17.8 micrograms/kg) was administered 20 min prior to acquisition, which was followed immediately by the test phase. In Task 2, the drug was administered immediately after acquisition, which was followed 20 min later by the test phase. Performance was impaired in a dose-related manner in Task 1, but not at all in Task 2, indicating that the effects of scopolamine on performance cannot be attributed to an impairment either in the retrieval of stored information or in the attentive or perceptual discriminative processes needed for such retrieval, or, by implication, for storage. In addition, the forgetting curves for scopolamine in Task 1 were parallel to those of the control sessions; i.e., the curves did not diverge with increasing delay intervals, indicating that scopolamine did not increase the rate of forgetting. Taken together, the results suggest that scopolamine interferes selectively with the initial storage of the information to be remembered.

Animals↗
PubMed1991

Effects of post-training ethanol and group housing upon memory of an appetitive task in mice.

It has been shown that post-training ethanol's facilitating effects upon memory disappeared if the mice were kept isolated after training. Since ethanol-treated mice were attacked by their cagemates, it has been hypothesized that the improved retention induced by ethanol resulted from an interaction between ethanol and group housing which added aversive information to training. To investigate the correctness of this interpretation, ethanol effects upon memory of an appetitive task were studied. C57BL/6J mice (isolated the day before training) were individually trained to find a cheese pellet placed in a corner of an open-field. Mice were injected intraperitoneally immediately after training with saline, 0.5, 1.5, or 2.0 g/kg of ethanol. They were then returned to their home cage and left alone, with another mouse, or with five other mice for 2 h after training. All mice were tested 24 h later for retention. Reductions in the number of pellet approaches or in the latency to eat the pellet were taken as measures of learning. Post-training ethanol disrupted retention of the appetitive task in a dose-related manner. Moreover disruption was greater in mice group housed after training. The results support the hypothesis that ethanol's post-training facilitating effects upon aversive memory may be due to added aversive information to the stimulus complex, rather than, or in addition, to enhanced storage of memory traces.

Animals↗
PubMed1991

Time-dependent sequential increases in [14C]2-deoxyglucose uptake in subcortical and cortical structures during memory consolidation of an operant training in mice.

Previous results have suggested that memory processing may involve the sequential activation of subcortical and cortical structures. To study this phenomenon, we have examined the immediate (15 min) and delayed (220 min) metabolic changes produced in BALB/c mice by a partial training session in a bar-pressing appetitive task, using the [14C]-2-deoxyglucose (2-DG) relative glucose uptake method. These relative metabolic changes were compared to the ones produced in several control groups: untrained animals, sham-conditioned animals, overtrained animals, and animals forced to walk on a moving belt (immediate and delayed condition). Animals were given a single intrajugular injection (5 microCi) of 2-DG either 5 min before or 3 h (delayed condition) after the second training session. Forty minutes after the 2-DG injection, the animals were sacrificed and their brains processed for autoradiography. At the 15-min delay, a large 2-DG labeling increase was found in partially trained animals for various subcortical areas (septum, diagonal band, hippocampus, thalamus, and mammillary bodies) while a much smaller increase was found in four cortical areas (frontal, cingulate, parietal, and sensory motor cortices). At the 220-min delay, we observed a large 2-DG labeling increase in cortical (frontal, pyriform, and cingulate cortices) and subicular areas while a moderate 2-DG labeling increase was observed in entorhinal cortex and the diagonal band. These results show that, shortly after training, subcortical structures are preferentially activated while cortical structures are much less activated. Three hours later, at a time when retention performances have been shown to improve spontaneously in the same strain of mice and in the same task, cortical structures are highly activated.

Animals↗
PubMed1991

Time-dependent effects of post-trial amphetamine treatment in rats: evidence for enhanced storage of representational memory.

Two studies were conducted to test the ability of post-trial amphetamine treatment to improve later recall in a nonaversively motivated task. These studies utilized 8- and 12-arm radial mazes, respectively, with an 11-h retention interval imposed after the rat traversed half the arms of the maze (termed, the to-be-remembered-event, or TBRE). In Experiment 1, the rats were injected with amphetamine (0, .25, and .50 mg/kg) immediately after the TBRE. Because the drug treatment improved retention, a time dependency study was conducted in which the drug (0 and .33 mg/kg) was administered 0, 3, and 6 h after the TBRE. The finding that amphetamine injection at 0, but not 3, h post-trial improved later recall indicates that the benefit derived from the former treatment is not due to proactive influences at the time of the retention test. Drug treatment 6 h post-trial produced a borderline improvement of recall; possible mechanisms are discussed. Two conclusions can be drawn from these results: (1) amphetamine administration can improve recall under conditions in which this effect cannot be attributed to alterations in information processing during either the learning or the retention sessions, indicating that the drug modulates memory storage processes; and (2) amphetamine treatment can improve working memory, thus excluding an alternative interpretation for the previous reports of impaired short-term memory in animals, all of which entailed assessments of working memory. The possibility remains, however, that the impairment seen in these tasks reflects the requirement for erasure of information from previous trials within each daily session, rather than the duration of the retention interval.

Amphetamine↗
PubMed1991

Amnesia induced by 2-deoxygalactose in the day-old chick: lateralization of effects in two different one-trial learning tasks.

2-Deoxy-D-galactose, an inhibitor of brain glycoprotein fucosylation, was injected intracranially (10 mumole dose in 10 microliters) into either the left or the right forebrain hemisphere of day-old chicks (Gallus domesticus). Bilateral injection of this dose of 2-deoxy-D-galactose is known to induce amnesia for several learning tasks including one-trial passive avoidance and sickness-induced learning. When a tritiated form of the drug was injected into one forebrain hemisphere only, a significantly large proportion of the dose remained in that hemisphere. Chicks were trained in two different one-trial learning tasks. The first was a passive avoidance task in which the chicks were allowed to peck at a green training stimulus (a small light-emitting diode, LED) coated in the bitter liquid, methylanthranilate, giving rise to a strong disgust response and consequent avoidance of the green stimulus. In the second paradigm the chicks were allowed to peck at a similarly colored dry stimulus but, 30 min later, were injected intraperitoneally with lithium chloride (0.1 ml of 1 M solution), causing a sickness-induced aversion for the green LED. 2-Deoxy-D-galactose caused amnesia for the passive avoidance task when injected before training into the right hemisphere but not the left. However, unilateral injection of the drug before training on the sickness-induced learning task did not cause amnesia. The results indicate that fucosylation of brain glycoproteins is required in the right hemisphere for learning the passive avoidance task but that memory for sickness-induced learning can be retained by either hemisphere.

Age Factors↗
PubMed1991

Naloxone eliminates passive avoidance retention deficits produced by pretest exposure to novelty in rats.

Pretest exposure to novelty or injections of beta-endorphin can enhance passive avoidance (PA) retention (e.g., Izquierdo & McGaugh, 1985). Enhanced retention may result from a "state-dependent" match between the CNS state during test and the novelty-induced beta-endorphin state that is obtained during training in a novel apparatus. Our Experiment 1 suggests that, unlike PA, Pavlovian fear conditioning in a conditioned lick suppression (CLS) paradigm may be beta-endorphin "state-independent." Rats were given one tone-shock pairing in a novel environment. Baseline lick rates and CLS tested 48 h later in a familiar environment were not affected by pretest exposure to novelty and/or injections of 3.33 mg/kg naloxone HCl. In Experiment 2, the same rats were PA trained/tested in a new apparatus. Saline or naloxone injections and various exposure (novel, familiar, none) conditions preceded (1h) the 24-h retention test. Pretest exposure to novelty reduced retention and naloxone eliminated that deficit. In Experiment 3, naive rats given pretest exposure to novelty also showed a PA retention deficit. The results of Experiments 2 and 3 may complement rather than contradict previous findings. Pretest induction of a beta-endorphin state by novelty may either enhance state-dependent retrieval of a "weak" memory trace or make a "strong/well consolidated" training memory more vulnerable to retroactive interference from "new learning" during the pretest exposure period.

Animals↗
PubMed1992

Learning of rats under amnesia caused by pentobarbital.

Dissociated learning of rats in the normal state and the state of amnesia produced by pentobarbital (15 mg/kg, ip) was carried out. Rats were trained to approach a shelf where they received food reinforcement. In Group 1 the rats were trained under the influence of pentobarbital to run to the same shelf as in the normal state. In Group 2 the rats were trained to approach different shelves in different drug states. It was shown that memory dissociation occurred in both groups. Differences in the parameters of training under the influence of pentobarbital between Groups 1 and 2 were revealed. These findings show that the brain-dissociated state induced by pentobarbital is formed with the participation of the mechanisms of information perception.

Animals↗
PubMed1992

Strategy selection in a task with spatial and nonspatial components: effects of fimbria-fornix lesions in rats.

The main purpose of the present research was to investigate the ability of rats to learn a 12-arm radial maze task that requires the concurrent utilization of both spatial and intramaze cue information. The task involves in a single trial both place and cue learning as well as reference memory (RM) and working memory (WM). Since the animal can choose place and cue arms in any order, the strategies employed to learn the task can be studied as well as the kinds of memory errors that are made. The results of Experiment 1 showed that the number of errors made on the place and cue components of the task did not differ, and that more RM than WM errors were made early during learning. As the task was learned, the animals tended to choose the place arms before choosing the intramaze cue arms, thus suggesting that a spatial strategy was employed first followed by a cue strategy. In Experiment 2 lesions of the fimbria-fornix resulted in temporary impairments in both RM and WM that were especially apparent on the spatial component of the task. The lesioned rats also switched from choosing mostly place arms early during the trial to choosing more cue arms. While fimbria-fornix lesioned rats recovered from the memory impairments with training, the change in response strategy persisted throughout postoperative testing. The procedure of combining both spatial and non-spatial components concurrently in the same task should prove of value in studying response strategies in animals.

Animals↗
PubMed1985

A comparison of the autonomic nervous control of the heart during classical aversive vs appetitive conditioning in dog.

Dogs were trained in either classical (i.e. Pavlovian) appetitive (n = 7) or aversive (n = 7) conditioning by presenting a tone (the conditional stimulus, CS +) that was followed by either food or shock delivery, respectively. In the first case, dog food was given to the animals during the last 30 s of a 1 min CS+. Aversive conditioning was accomplished by giving a 1 s shock at the end of a 30 s CS+. The control consisted of a different tone (CS-) which was never followed by food or shock. A chronically implanted transducer was used to record left ventricular pressure from which its first time derivative was calculated; d(LVP)/dt was used as an index of myocardial inotropic state. Heart rate (HR) was also determined. These data were averaged over the 30 s prior to the CS+, the 30 s of the conditional stimulus tone itself, and the 30 s following shock or during food delivery. Well-trained animals evidenced changes in cardiac inotropism and chronotropism during the CS+ and also in response to unconditional shock or food; these are referred to as the conditional and unconditional cardiovascular responses, respectively. No statistically significant HR or d(LVP)/dt changes were observed during the CS-. The conditional response to food was small: relative to the pre-CS+ interval, average HR increased 11 bpm (P less than 0.05) and average d(LVP)/dt increased 309 mm Hg/s (P less than 0.01). During food delivery, HR increased by additional 23 bpm (P less than 0.01) and d(LVP)/dt increased by another 232 mm Hg/s (P less than 0.01). Beta-adrenergic blockade virtually eliminated the conditional HR and d(LVP)/dt response to food, indicating that both the chronotropic and inotropic changes during CS+ were due to elevated sympathetic drive. beta-blockade did not eliminate the unconditional HR response (+17 bpm, P less than 0.01), indicating that parasympathetic withdrawal has a mediating role in this persisting tachycardia. The conditional response to shock consisted of a 26 bpm increase in HR (P less than 0.01), while d(LVP)/dt increased 998 mm Hg/s (P less than 0.01). The beta-blockade reduced the HR conditional response to +8 bpm (NS) and essentially eliminated the increase in d(LVP)/dt. These data indicate that increases in cardiac sympathetic tone play a primary role in mediating the conditional cardiovascular response for both paradigms. Parasympathetic withdrawal, on the other hand, figures critically in mediating the unconditional response to food.

Animals↗
PubMed1983

Can aversive properties of (peripherally-injected) vasopressin account for its putative role in memory?

Rats injected with arginine vasopressin (AVP) immediately after exposure to a novel open-field environment found a water tube faster than saline injected rats, when water-deprived 48 h later. Other experiments demonstrated that this effect did not result from some conditioned or pharmacologically-induced hyperactivity in the experimental group. Although these results are consistent with a role for AVP in 'memory' mechanisms, lithium chloride, a known illness-producing agent, produced a reduction in latency to find the water tube identical to that of AVP. In separate experiments, AVP acted as an effective unconditioned stimulus in conditioned taste and place aversion studies. AVP also produced a dose-dependent disruption of spontaneous locomotor activity. Together, these data indicate that peripheral AVP administration has aversive consequences. Desglycinamide arginine vasopressin (an AVP analog with weak pressor-agonist properties) produced no observable aversive effects and did not improve test performance in the appetitive water-finding task. It is suggested that the apparent memory-enhancing properties of peripherally administered AVP, at least in appetitive test paradigms, may depend on its aversive and consequently arousing actions.

Animals↗
PubMed1983

Handling in infancy, brain laterality and muricide in rats.

Rats were handled for the first 20 days of life or were not disturbed. Between 21 and 50 days approximately half of each group was reared in enriched environments while the remainder was group reared in laboratory cages. When adult, four males from each litter received a right neocortical ablation, a left ablation, a sham operation, or no surgery. They were tested for mouse killing between 9-12 months of age. Intact non-handled controls without enrichment experience had a 96% incidence of muricide. Handling and enrichment treatments independently and additively reduced the rate of mouse killing in animals with intact brains. There was no evidence of brain laterality for animals which received no extra stimulation in early life. In contrast, the brains of handled animals were lateralized, with the left lesion group having a higher killing response than the right. Non-lesioned handled rats had approximately the same level of muricide as those with a right hemisphere lesion, leading to the inference that in the intact brain the left hemisphere inhibits the killing response of the right.

Aggression↗
PubMed1987

Vasopressin metabolite neuropeptide facilitates simultaneous temporal processing.

Rats were trained on a peak-interval timing procedure in which auditory, tactile, and visual stimuli signaled 3 different fixed-interval schedules (15, 30, and 60 s) that were presented simultaneously in a hierarchical fashion. Administration of vasopressin metabolite neuropeptide [pGlu-Asn-Cys(Cys)-Pro-Arg-Gly-NH2, 0.3 microgram/kg i.p.] had two main effects on performance. With repeated exposure the temporal criterion for each of the intervals shifted leftward on the time scale in a proportional manner, and the probability of attention to each of the intervals increased proportionally. The conclusion is that vasopressin metabolite neuropeptide facilitates simultaneous temporal processing by increasing the speed of mental processes involved in memory storage and divided attention. These results indicate that a major metabolite of arginine vasopressin that is devoid of endocrine and pressor activity can produce facilitation of cognitive processes in animals.

Animals↗
PubMed1988

Improvement of memory for an operant response by post-training glucose in mice.

Previous experiments have shown that a post-training glucose injection can retroactively and non-contingently improve the retention of a previously learned association. To date, the memory-improving action of glucose has only been demonstrated in rats for negatively-motivated tasks. The present experiment sought to generalize these previous results by examining the effects in mice of post-training glucose injections on the retention of an operant bar-pressing response. The results show that post-training glucose can retroactively and non-contingently improve the retention of an appetitively motivated task in mice. There was a U-shaped relationship between the dose of glucose and the effect on memory similar to the ones already observed in rats using negatively motivated training. The implications of these results for an endogenous memory modulation mechanism are discussed.

Animals↗
PubMed1988

Drug-induced place preference in rats with 5,7-dihydroxytryptamine lesions of the nucleus accumbens.

The conditioned place preference (CPP) paradigm was used to determine a role for serotonin in the nucleus accumbens in the mediation of the rewarding properties of D-amphetamine morphine and diazepam. The effect of these drugs on CPP was examined in controls and in animals with 5,7-dihydroxytryptamine lesions of the nucleus accumbans. The results from control animals confirmed that D-amphetamine (1.5 mg/kg, i.p.), morphine (2.0 mg/kg, i.p.) and diazepam (1.0 mg/kg, i.p.) produced place preference for a distinctive environment that had previously been paired with injections of the drug. In animals with 80% reduction of 5-hydroxytryptamine content of the nucleus accumbens, D-amphetamine CPP was unchanged and morphine CPP was attenuated compared with controls. Diazepam CPP was not apparent in animals with the lesion. In separate experiments, characteristic behavioural effects of the drugs under study were examined in control and in animals with lesion. The results showed a tendency for increased amphetamine hyperlocomotion, enhanced morphine activity and analgesia and decreased diazepam anti-anxiety effect in animals with lesions. Thus, the 5,7-dihydroxytryptamine lesions of the nucleus accumbens differently influenced the CPP induced by the drugs studied and, with the exception of diazepam, the various behavioural effects elicited by each drug. The findings suggest that serotonin-containing neurones of the nucleus accumbens are a component of the neural circuitry that mediates the rewarding properties of morphine, probably of diazepam, but not of D-amphetamine.

5,7-Dihydroxytryptamine↗