Showing papers in "Behavioral Neuroscience in 1988"

Reciprocal effects of hormonal fluctuations on human motor and perceptual-spatial skills.

Abstract: Normal adult women showed systematic performance fluctuations across the menstrual cycle on several motor and perceptual tests that typically yield sex differences in performance. The midluteal phase, characterized by high levels of estradiol and progesterone, was associated with improved performance on tests of speeded motor coordination and impaired performance on a perceptual-spatial test, relative to performance during menses. Variations in gonadal steroid levels may contribute substantially to the sex differences reported in human cognitive and motor skills.

The catalepsy test: its ups and downs.

Abstract: The typical catalepsy test consists of placing an animal into an unusual posture and recording the time taken to correct this posture. This time is regarded as an index of the intensity of catalepsy. Catalepsy is a robust behavior, and the lack of standardization does not usually hinder its actual detection. However, the intensity of the cataleptic effect is influenced by minor methodological differences, and thus interpretation and comparison of results across laboratories are difficult. The behavioral catalepsy test can use any of several different apparatus, including wire grids, parallel bars, platforms, or pegs, to situate the animals in unusual positions. The most common, however, is the "bar test," and despite its wide use in psychopharmacological research, even parameters of this test are not standardized. The present article reviews the wide variety of parameters chosen by investigators that measure catalepsy. The methodological issues of repeated testing, scaling of scores, apparatus, animal weight, maximal test duration, behavioral criteria, and other influences are discussed. In addition, a brief review of the neuropharmacological basis of catalepsy is also included. Finally, it is argued that a universal, standardized bar test be adopted by researchers. New data on a novel automated bar test in the Digiscan Activity Monitoring System is presented.

Hippocampal system dysfunction and odor discrimination learning in rats: impairment or facilitation depending on representational demands.

Abstract: The performance of normal rats and that of rats with hippocampal system damage were compared on acquisition of different versions of the same two-odor discrimination task that placed different encoding and representational demands on memory. Rats with fornix lesions were impaired when explicit comparisons among multiple odor cues and differential response choices were encouraged. However, when odor-cue comparison was hindered and explicit cues for response choice were eliminated, rats with fornix lesions out performed normal animals. The results support an hypothesis that the hippocampal system is critical to a memory representation based on encoding relations among multiple percepts, and other brain systems support performance adaptations based on encodings of stimuli individually.

Human amnesia and animal models of amnesia: performance of amnesic patients on tests designed for the monkey.

Abstract: The performance of amnesic patients was assessed on five tasks, which have figured prominently in the development of animal models of human amnesia in the monkey. The amnesic patients were impaired on four of these tasks (delayed nonmatching to sample, object-reward association, 8-pair concurrent discrimination learning, and an object discrimination task), in correspondence with previous findings for monkeys with bilateral medial temporal or diencephalic lesions. Moreover, performance of the amnesic patients correlated with the ability to verbalize the principle underlying the tasks and with the ability to describe and recognize the stimulus materials. These tasks therefore seem to be sensitive to the memory functions that are affected in human amnesia, and they can provide valid measures of memory impairment in studies with monkeys. For the fifth task (24-hour concurrent discrimination learning), the findings for the amnesic patients did not correspond to previous findings for operated monkeys. Whereas monkeys with medial temporal lesions reportedly learn this task at a normal rate, the amnesic patients were markedly impaired. Monkeys may learn this task differently than humans.

Phantom auditory sensation in rats: an animal model for tinnitus.

Abstract: In order to measure tinnitus induced by sodium salicylate injections, 84 pigmented rats, distributed among 14 groups in five experiments, were used in a conditioned suppression paradigm. In Experiment I, all groups were trained with a conditioned stimulus (CS) consisting of the otT set of a continuous background noise. One group began salicylate injections before Pavlovian training, a second group started injections after training, and a control group received daily saline injections. Resistance to extinction was profound when injections started before training, but minimal when initiated after training, which suggests that salicylate-induced etTects acquired ditTerential conditioned value. In Experiment 2 we mimicked the salicylate treatments by substituting a 7 kHz tone in place of respective injections, resulting in effects equivalent to salicylate-induced behavior. In a third experiment we included a 3 kHz CS, and again replicated the salicylate findings. In Experiment 4 we decreased the motivational level, and the sequential relation between salicylate-induced effects and suppression training was retained. Finally, no salicylate etTects emerged when the visual modality was used. These findings support the demonstration of phantom auditory sensations in animals.

Impaired learning of a motor skill in patients with Huntington's disease.

Abstract: The ability of patients with Huntington's disease (HD), patients with dementia of the Alzheimer's type (DAT), and amnesic patients (AMN) to acquire the motor skills underlying a pursuit rotor task was assessed. Differences between groups in initial levels of performance were minimized by adjusting the rotation speed of the disk. The HD and DAT groups were also administered a verbal recognition span test. The results showed that the DAT, AMN, and intact control groups all significantly improved their time on target over six test blocks whereas the HD group was severely impaired in the acquisition of this motor skill. On the verbal recognition span test, the DAT and HD groups were significantly and equally impaired, but the HD group evidenced better immediate and delayed recall than did the DAT group. These results provide further evidence that the basal ganglia are critically involved in the acquisition of motor skills.

Double dissociations of the effects of amygdala and insular cortex lesions on conditioned taste aversion, passive avoidance, and neophobia in the rat using the excitotoxin ibotenic acid.

Abstract: The results in this article show that although electrolytic amygdala lesions disrupt learning of a conditioned taste aversion (CTA), ibotenic acid-induced, axon-sparing lesions of the amygdala do not. However, ibotenic acid lesions of the insular cortex do disrupt learning of a CTA. Electrolytic, but not ibotenic acid lesions of the amygdala, interrupt axons running between the insular (gustatory) cortex and the brain stem/hypothalamus. It is the destruction of these projections which appear to underly CTA deficits after amygdala lesions. Other results revealed that ibotenic acid lesions of the insular cortex attenuated the reaction to the novel taste of saccharin in a familiar environment but failed to affect the ingestion of a novel food in a novel environment or passive avoidance learning. Conversely, ibotenic acid lesions of the amygdala did not affect the reaction to novel saccharin in a familiar environment but did impair both the reaction to novel food in a novel environment and passive avoidance learning. We conclude that the insular cortex is involved in reactions to the novelty and associative salience exclusively of taste stimuli, whereas the amygdala is probably more concerned with the reaction to more general aspects of novelty in the environment and in fear-motivated behavior.

Double-blind versus deceptive administration of a placebo.

Abstract: Subjects were given varying doses of a placebo, consisting of decaffeinated coffee, with double-blind or deceptive instructions. Deceptive administration simulated clinical situations in that subjects were led to believe that they were receiving an active drug. In contrast, subjects in double-blind conditions were aware that they might receive a placebo. Double-blind and deceptive administration of the placebo produced different, and in some instances, opposite effects on pulse rate, systolic blood pressure, and subjective mood. Deceptive administration produced an increase in pulse rate, whereas double-blind administration did not. A theoretically predicted curvilinear effect on systolic blood pressure, alertness, tension, and certainty of having consumed caffeine was confirmed with deceptive administration, but not with double-blind administration. Double-blind administration produced curves in the opposite direction on each of these variables. The effects of the placebo on motor performance varied as a function of subject's beliefs about the effects of caffeine. These data challenge the validity of double-blind experimental designs and suggest that this common method of drug assessment may lead to spurious conclusions.

Maternal deprivation potentiates pituitary-adrenal stress responses in infant rats.

Abstract: In three experiments we examined the effect of maternal deprivation on the pituitary-adrenal response of 12-, 16- and 20-day-old rat pups to novelty stress. Infant rats were either deprived individually in heated incubators or left in the home nest with their mother and then tested for their corticosteroid response to 30-min exposure to a novel test arena (novelty-stress). In Experiment 1 we showed that the magnitude of the stress response was a positively accelerated function of the deprivation interval. Stress responses were not increased after 1 hour of deprivation, were modestly increased after 8 hours of deprivation, and were dramatically increased after 24 hours of deprivation. In Experiment 2 we asked whether potentiation of the stress response resulted from the maternal or the nutritive components of the deprivation procedure. Pups were tested under one of four treatment conditions formed by a 2 (Maternally Deprived vs. Nondeprived) x 2 (Nutritively Deprived vs. Nondeprived) factorial design. At 12 and 16 days of age, potentiation of the stress response was traced to the absence of maternal care and not nutrients. At 20 days of age, both maternal and nutritive deprivation contributed to the potentiated stress response. The results of Experiment 3 showed that this effect was mediated, at least in part, by increased adrenocortical sensitivity to ACTH, because the corticosteroid response to exogenous ACTH administration was also increased by maternal deprivation. These findings add to a growing body of literature that supports the concept of maternal regulation of infant physiology. They also support previous reports from this laboratory indicating that suppression of the pituitary-adrenal system is modulated by maternal variables during the preweaning period in the rat.

Spatial cognitive maps: differential role of parietal cortex and hippocampal formation.

Abstract: Separate groups of rats with lesions in the parietal cortex (PC) or hippocampal formation (HF) were tested for acquisition and retention of the Morris water maze cognitive mapping task. Some of the animals in each lesion group received preoperative training in the task. Other animals in each group received no preoperative training. The results indicate that although both lesions lead to a cognitive mapping impairment in both the acquisition and retention of the task, the animals with PC lesions were more severely impaired than were the animals with HF lesions, as indicated by quantitative measures. However, qualitative aspects of the animals' swim behavior indicate that the HF damaged animals tend to use "nonmapping" strategies to solve the tasks, which suggests that the qualitative nature of their impairment differs from that of the PC damaged animals. The results of this study support the hypothesis that PC plays an important role in the processing of information about space that is allocentric or external to the body.

Conditional analgesia, defensive freezing, and benzodiazepines.

Abstract: When rats are placed in a situation that has come to be associated with footshock through the process of Pavlovian conditioning, they react with the species-specific defensive response of freezing and a reduction in sensitivity to painful stimulation. In the present experiments, the effects of three benzodiazepines on both of these responses were examined. Pain sensitivity was measured with the formalin test. Concurrent observations of formalin-induced recuperative behavior and freezing were recorded while the animals were in the presence of shock-associated contextual stimuli. It was found that midazolam (Experiments 1 and 2), chlordiazepoxide (Experiment 3), and diazepam (Experiment 4) were capable of significantly attenuating the conditional analgesia. Midazolam and diazepam also reduced the freezing response. The finding that these anxiolytic agents attenuate both conditional responses suggests that the freezing and analgesia are mediated by a common fearlike process.

Dissociation of associative and nonassociative concomitants of classical fear conditioning in the freely behaving rat.

Abstract: An acoustic stimulus previously paired with footshock elicits stereotyped increases in arterial pressure and heart rate and induces freezing behavior in freely behaving rats. Although the arterial pressure and freezing responses differ between groups given paired and random presentations of the tone and shock, the increases in heart rate do not. These observations, if taken at face value, suggest that the arterial pressure and freezing responses reflect associative learning but that the heart rate change is a nonassociative or a pseudoconditioned response. In this article we describe three experiments aimed at determining why the CS elicits similar increases in heart rate in groups given paired and random training. The first study demonstrates that regardless of the pseudoconditioning control procedure used (random, backwards, shock-alone, or naive), the same pattern of results is obtained: the increases in arterial pressure are greater in the paired than in each control group, but the heart rate rises to the same extent in all groups. The second study determined that the context in which the responses are tested (conditioning apparatus vs. novel test chamber) does not affect the general pattern of results obtained. The third study demonstrates that the superficially similar increases in heart rate in conditioned and pseudoconditioned rats are achieved by different physiological mechanisms: coactivation of the sympathetic and parasympathetic nervous systems in conditioned rats and sympathetic excitation alone in pseudoconditioned rats. Thus, the heart is influenced by associative emotional processes, but heart rate is not, under these conditions, a particularly useful index of those influences.

Enhancement of acoustic startle by electrical stimulation of the amygdala.

Abstract: The present study demonstrated that electrical stimulation of the amygdala enhanced the acoustic startle response A 25-ms train of 01-ms pulses initiated 5 ms before the onset of a 20-ms noise burst significantly increased startle at currents from 40 to 400 microA Electrode placements just medial to the amygdala (in the pathway connecting the amygdala to the brain stem) increased startle with the lowest currents Startle was also increased in all animals with stimulation in the central, medial, and intercalated nuclei of the amygdala Stimulation in areas surrounding the amygdaloid complex was ineffective In a second experiment, paired pulses with interpulse intervals between 01 and 200 ms delivered to the amygdala demonstrated that the stimulated axons had a distribution of refractory periods between 06 and 10 ms This suggests that the population of neurons which subserves the enhancement of acoustic startle is fairly homogeneous and has small, myelinated axons

Axon-sparing lesions of the preoptic region and substantia innominata disrupt maternal behavior in rats.

Abstract: In this study we investigated the effects of axon-sparing lesions of the preoptic region on the maternal behavior of postpartum rats. The lesions were produced with the excitotoxic amino acid N-methyl-D,L-aspartic acid (NMA). The first experiment determined that bilateral injections of NMA into the medial preoptic area (MPOA) of fully maternal lactating rats disrupted maternal behavior. In a second experiment, bilateral injections of NMA into the lateral preoptic area and adjoining substantia innominata (LP/SI region) also disrupted maternal behavior. A third experiment, employing horseradish peroxidase histochemistry, provided anatomical evidence that NMA destroys neuronal cell bodies while sparing fibers of passage. These findings were discussed with respect to the view that an MPOA-to-LP/SI-to-ventral tegmental area circuit underlies maternal behavior in the rat.

Hippocampal and amygdaloid involvement in working memory for nonspatial stimuli

Abstract: Hippocampal lesions in rats lead to an impairment of performance in spatial delayed conditional discriminations. The effect of such lesions on nonspatial tasks is controversial. In monkeys, both the hippocampus and the amygdala are involved in nonspatial delayed conditional discriminations. The effect of amygdaloid lesions in rats on this type of task has not been studied. To clarify the role of hippocampus and amygdala in a cue-relevant/space-irrelevant delayed conditional discrimination, rats were trained on a delayed match-to-sample task with visual and tactile cues as discriminative stimuli. Rats were then given one of five lesions: control, complete fimbria-fornix, partial fimbria-fornix, complete amygdala, or partial amygdala. Amygdaloid lesions, partial or complete, did not impair choice accuracy. Fimbria-fornix lesions did impair choice accuracy, and the magnitude and duration of the impairment was a function of the size of the lesion. Partial fimbria-fornix lesions produced a slight impairment that disappeared with continued testing. Complete fimbria-fornix lesions produced chance performance throughout postoperative testing. These results indicate that the fimbria-fornix, but not the amygdala, is involved in nonspatial delayed match-to-sample.

Bilateral cerebellar lesions disrupt conditioned eyelid responses in unrestrained rats

Abstract: Electromyographic eyelid responses in unrestrained rats were classically conditioned in a Pavlovian delay paradigm by using a tone conditioned stimulus (CS) and periorbital shock unconditioned stimulus (US). After eyelid conditioning was complete, bilateral electrolytic lesions were made in the dentate-interpositus region of the cerebellar nuclei. Initial eyelid conditioning was reliable and very similar to that previously observed in the rabbit, although the asymptotic eyelid responses contained a short-latency startle response in addition to the usual conditioned and unconditioned responses (CR and UR). Substantial decrements in CRs were observed in 13 of the 14 rats with accurately placed lesions. In contrast, startle responses and URs were unaffected. The results replicate the effects of cerebellar lesions on eyelid CRs in the rabbit and suggest that the anatomical basis of eyelid conditioning in both species is similar.

Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: a tool for the neural analysis of taste-visceral associations.

Abstract: Several explanations may account for deficits in the ability of animals to form taste aversions following neural manipulations. These encompass impairments in conditioned stimulus (CS) and unconditioned stimulus (US) processing, conditioned response (CR) measurement, and expression, memory, and taste-visceral integration. A behavioral procedure that aids in the distinction between some of these possibilities is presented. In Experiment 1, 10 rats received seven intraoral (IO) infusions of sucrose (30 s, 0.55 ml) spaced every 5 min starting immediately after the injection of 3.0 mEq/kg of lithium chloride (LiCl). Control rats (n = 12) were treated identically except that they were injected with sodium chloride (NaCl). Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected rats systematically decreased their ingestive taste reactivity behavior over time, whereas aversive behavior increased. Control rats maintained high and stable levels of ingestive responding and demonstrated virtually no aversive behavior over the 30-min period following sodium injection. Rats were tested several days later for the presence of a conditioned taste aversion (CTA). Rats previously injected with lithium during sucrose infusions demonstrated significantly more aversive behavior than the control group, which demonstrated none. There were no differences in the level of ingestive behavior displayed by the two groups on the CTA test. Experiment 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, a difference in the ingestive behavior between the two groups was observed. In Experiment 2, naive rats were injected with either NaCl or LiCl but did not receive their first sucrose infusion until 20 min later. These rats also received sucrose infusions at 25 and 30 min postinjection. There were no differences in the taste reactivity behavior displayed by lithium- or sodium-injected rats during any of the sucrose infusions. Collectively, these findings indicate that rats dramatically change their oromotor responses to sucrose during the period following LiCl administration, provided that the infusions start immediately after injection. Furthermore, this time-related behavioral change is predominantly attributable to associative processes. This paradigm can be useful in distinguishing between neural manipulations that affect the establishment of taste-visceral associations from others that affect the animal's ability to retain such associations over the commonly employed 24-hr conditioning-test interval.

Variations in human corpus callosum do not predict gender: a study using magnetic resonance imaging.

Abstract: Controversy exists in the neuropsychological literature concerning the existence of gender-associated differences in cognitive functioning and in hemispheric lateralization of cognitive functions. A recent study, based on 14 brains obtained at autopsy, reported sex differences in the splenium of the human corpus callosum and suggested that the larger splenium in females reflects less hemispheric lateralization, or "specialization," than the male brain for visuospatial functions. Our measurements of the human corpus callosum using magnetic resonance images of 37 living subjects failed to confirm reported sex differences in the splenium. A marginally significant sex-related difference in minimum body width and an age-related decrease in anteroposterior distance were found. Most striking were the large variations in callosal size and shape among individuals regardless of age or gender. Existing knowledge of the functions of the corpus callosum does not permit correlations between variations in callosal size and shape and variations in cognitive functions.

Hippocampal function is required for feedback control of an internal clock's criterion.

Abstract: Columbia University A discrete-trial peak-interval procedure was used to evaluate the effects of hippocampal damage on the control of an internal clock's criterion. Rats first received either lesions of the fimbria- fornix or sham operations. Following surgery rats were trained on a 20-s peak-interval procedure and later were transferred to a 10-s peak-interval procedure. Rats with sham operations were maximally responsive about the time that reinforcement was sometimes made available (10 or 20 s) and showed an oscillation of successive peak-time values similar to biological feedback control systems. In contrast, rats with fimbria-fornix lesions were maximally responsive at a time about 20% earlier than the time that reinforcement was made available (8 or 16 s) and showed no control of successive peak-time values. Taken together, these results demonstrate that a fimbria-fomix lesion reduces the remembered time of reinforcement stored in reference memory, interferes with the internal control of temporal criteria stored in working memory, and has no effect on the animal's sensitivity to stimulus duration or the acquisition of a new temporal criterion. One of the behavioral procedures that has been used to investigate the brain mechanisms involved in temporal proc- essing is the discrete-trial peak-interval (PI) procedure, a mod- ification of the standard fixed-interval (FI) procedure. In the PI procedure, after an intertrial interval (ITI) a signal occurs, and the rat is free to make a lever response at any time while the signal is present. On a random half of the trials, the first lever response after a fixed duration has elapsed (e.g., 20 s) terminates the signal and produces food reinforcement. On the remaining trials, no reinforcement is primed, and the signal continues for a relatively long time. The PI procedure is designed to provide independent measures of several proc- esses involved in duration discrimination. On the trials in which there is no reinforcement primed (peak trials), the rat's response rate increases as a function of signal duration until a point near the time that reinforcement is sometimes made available, and then it decreases in a fairly symmetrical man- ner. The time that the response rate is maximal is called the

Stressor-provoked behavioral changes in six strains of mice.

Abstract: Behavioral changes induced by inescapable shock were examined in six strains of mice. Exposure to shock provoked time-dependent disturbances of shuttle escape performance. In some strains the shock treatment did not affect escape performance, whereas in others profound performance deficits were evident. The inescapable shock treatment likewise induced strain-dependent alterations of performance in a forced-swim task. In most instances the shock treatment initially provoked invigorated responding, but in other strains the shock had no effect or depressed active responding. Finally, Y-maze spontaneous alteration performance was not affected by the shock treatment, although a strain-dependent increase of perseverative responses was evident. The occurrence of a stressor-induced deficit in one task in a particular strain of mouse was not predictive of behavioral alterations in a second task. These data are discussed with respect to animal models of depression and genetic differences associated with the response to stressors.

The estrous cycle and estrogen modulate stress-induced analgesia.

Abstract: In this article we investigate the impact of estrous cycle, ovariectomy, and estrogen replacement on both opioid and nonopioid stress-induced analgesia. Stage of estrous strongly influenced analgesia. Diestrus females exhibited the typical male pattern produced by the analgesia inducing procedures used--strong nonopioid analgesia following 10-20 tailshocks, and strong opioid analgesia following 80-100 tailshocks. In these experiments the nonopioid analgesia was slightly attenuated during estrus, but the opioid analgesia was markedly reduced. The role of estrogen in producing these changes was studied with estrogen replacement in ovariectomized subjects. Ovariectomy only slightly altered nonopioid analgesia but eliminated opioid analgesia, which suggests that some estrogen might be necessary to maintain the integrity of the system(s) underlying opioid analgesia. Estrogen administration restored opioid analgesia, but further estrogen suppressed opioid analgesia, duplicating the estrus pattern. It did not suppress nonopioid analgesia. Opioid analgesia was enhanced 102 hr after estrogen replacement, thus duplicating the diestrus pattern. Estrogen thus appears to be responsible for the impact of estrous cycle on opioid but not on nonopioid analgesia. These results suggest that ovarian hormones may modulate the impact of stressors on endogenous pain inhibition and other stress-responsive systems.

Acoustic startle response in young and aging C57BL/6J and CBA/J mice.

Abstract: C57BL/6J (C57) mice demonstrate progressive age-related hearing loss during the first year of life, whereas CBA/J (CBA) mice lose little sensitivity through 18 months of age. The acoustic startle response (ASR) was measured in these strains to determine behavioral correlates of aging with and without presbycusis. The stimuli were tone pips (10-ms duration, 1-ms rise-fall) with frequencies of 4, 8, 12, 16, or 24 kHz at intensities of 70, 80, 90, or 100 dB SPL. ASR "thresholds" (the minimum SPL required to elicit ASRs more than 50% of the time) increased with age, and startle amplitudes became smaller in both strains. However, the changes in these startle parameters were much more pronounced in C57 mice, with middle to high frequencies (12-24 kHz) severely affected. The startle latencies at and above ASR "threshold" increased with age in C57 mice, but did not change in CBA mice. The CBA data indicate that aging, per se, has little effect on ASR parameters; the C57 data show that hearing loss is a cogent factor. However, ASR parameters of C57 mice are altered to a greater extent than expected, on the basis of the elevations of absolute sensory thresholds, particularly for middle frequencies (12-16 kHz). Both peripheral and central mechanisms are proposed to account for the discrepancy.

Behavior of rat fetuses following chemical or tactile stimulation

Abstract: The behavior of fetal rats was examined on Day 19 of gestation with procedures that enabled chemical stimulation and direct observation of fetuses. Rat fetuses are sensitive to both tactile stroking and intraoral infusion of chemical solutions, but the pattern and amount of activity depend upon the modality of stimulation. Fetal responsiveness is affected by prior experience with chemical stimuli. Repeated exposure within a 10-min period results in a waning of response, and repeated exposure across a delay of 48 hr results in a different pattern of response than is seen to a novel stimulus. Reexposure to a stimulus experienced earlier in gestation also alters fetal responsiveness to other forms of tactile and chemical stimulation. These findings indicate that the rat fetus exhibits olfactory function in utero and suggest central processing of sensory information, including evidence of habituation, a fetal orienting reflex to novel stimuli, and the existence of prenatal behavioral states associated with different patterns of response.

Premotor cortex in the rat

Abstract: Donoghue and Wise (1982) identified an area AGm in the rat that they take to be a nonprimary motor area. In the present experiments, therefore, this area was removed bilaterally in rats. The animals were poor at relearning a visual conditional motor task but were able to learn spatial delayed alternation as rapidly as unoperated animals. Thus removing this area in rats has a similar effect to removing premotor cortex in monkeys. It is argued that this dorsomedial shoulder area should not be regarded as part of prefrontal cortex in the rat.

Aging and atropine effects on spatial navigation in the Morris water task.

Abstract: A recent animal model that has been particularly useful in the neurobiology of aging has been the age-related decline of spatial information processing capacity in Sprague-Dawley rats measured in the place-learning water task developed by Morris (1981). In the first experiment of the present study, place behavior was examined in young (6 months), old (23-24 months), and very old (28 months) rats of another strain, Long-Evans. As an analogue of aging-related cholinergic dysfunction the effects of atropine sulfate (5-50 mg/kg), an anticholinergic drug that is known to disrupt behavior in this task, also was determined. Place navigation was not impaired in undrugged rats, even those in the oldest age group. Rats treated with atropine showed dose-dependent deficits. In a second experiment, young (4-5 months), old (18-20 months), and very old (28 months) Fischer-344 rats were examined. Place navigation was impaired in the old rats. The very old (28 months) rats could not swim well enough to be tested adequately. Although nonspatial deficits associated with aging may be found across most strains tested, there appear to be very large strain-related differences in spatial processing ability as a function of age.

Medial septal lesions disrupt spatial mapping ability in rats.

Abstract: Rats with lesions of the medial septum were more likely to begin swimming in the wrong direction, swim farther, and, therefore, require more time to find a platform hidden in a Morris water tank than were control rats. Although the performance of the rats with medial septal lesions did improve over trials, their asymptotic performance also failed to equal that of the controls. Movement of the platform to a new position in the tank disrupted the performance of both groups, and, again, the rats with medial septal lesions were slower to locate the moved platform. However, this deficit was completely eliminated when a visual cue indicating the location of the moved platform was introduced. We suggest that these data indicate that damage to the septo-hippocampal cholinergic projection system produces a deficit in the formation or utilization of a spatial map (reference memory) that represents the location of a place with respect to the surrounding distal cues.

Motor Activity Changes Following Cerebral Ischemia in Gerbils Are Correlated With the Degree of Neuronal Degeneration in Hippocampus

Abstract: Cerebral ischemia was induced in Mongolian gerbils by bilateral occlusion of the carotid arteries. Subsequent histological assessment revealed neuronal degeneration in the CA1 area of the hippocampus. A functional .behavioral change was reflected in an elevation of motor activity compared with sham-operated animals. The degree of hippocampal damage was positively correlated with the increase in motor activity. It is concluded that alterations in both measures result from the interruption of blood flow to the brain but may be brought about by different mechanisms. The induction of cerebral ischemia in Mongolian gerbils by bilateral occlusion of the carotid arteries has been used as a model for stroke in humans (Kirino, 1982). A period of transient occlusion followed by resumption of blood flow results in cell loss in many areas of the brain, especially the CA1 area of hippocampus (Suzuki, Yamaguchi, Kirino, Orzi, & Klatzo, 1983). Functional deficits following carotid occlusion have also been identified, including hypermotility, perseveration, and hypoalgesia (Robinson, Shoemaker, Schlumpf, Valk, & Bloom, 1975; Tang, 1985). The most prominent behavioral change following forebrain ischemia in the gerbil is a large increase in motor activity, evident at 24 hr postocclusion and gradually diminishing to normal after about 5 days (Chandler, DeLeo, & Carney, 1985). Although the neuronal cell loss and the locomotor changes would both appear to be sequelae of the disruption of blood flow, no statistical correlation between the two events has been reported. In this experiment, we undertook a systematic evaluation of the relation between the degree of neuronal degeneration in the CA1 area of hippocampus and increased motor activity following bilateral carotid occlusion in gerbils.

The role of mesolimbic dopamine in conditioned locomotion produced by amphetamine.

Abstract: Daily administration of psychomotor stimulants in a distinctive environment can impart on the environment stimulantlike properties. Rats injected with amphetamine (0.75 mg/kg, sc) daily for 5 days exhibited a robust unconditioned locomotor response, measured in photocell cages, and showed a conditioned locomotor response when treated with saline on the 6th day. This conditioned locomotor response was found to be significantly attenuated by 6-hydroxydopamine (6-OHDA) lesions of the nucleus accumbens when the lesion was made either pre- or postconditioning. Similarly, although rats with 6-OHDA lesions of the nucleus accumbens exhibited a robust supersensitive unconditioned locomotor hyperactivity in response to apomorphine (0.1 mg/kg, sc), they did not show a conditioned response on the test day. These results suggest that the mesolimbic dopamine system may be responsible for both the unconditioned and conditioned locomotor responses to psychomotor stimulant drugs. Further, conditioned locomotion depends on a critical interaction between the physiological release of presynaptic dopamine and occupation of postsynaptic receptors.

Memory enhancement with posttraining intraventricular glucose injections in rats.

Abstract: Recent findings suggest that peripheral epinephrine enhancement of memory storage may be mediated in part by an increase in circulating glucose levels subsequent to epinephrine release or injection. Because glucose, unlike epinephrine, has ready access to the central nervous system, it is possible that glucose acts directly on central processes to enhance memory. To test this possibility, rats were trained on a one-trial inhibitory avoidance task and received immediate or delayed injections of glucose in artificial cerebrospinal fluid. On retention tests 24 hr after training, animals that received 3 or 5 micrograms glucose (in 1 microl cerebrospinal fluid over 3 min) had significantly enhanced performance of the learned response. These findings are consistent with the view that glucose can regulate the storage of new information by acting on central processes. Whether there are additional peripheral contributions to glucose effects on memory remains to be determined.

P3-like brain waves in normal monkeys and in monkeys with medial temporal lesions.

Abstract: The human brain produces a characteristic electrical response to relevant events that occur unexpectedly. Recent reports have suggested that a prominent part of this event-related brain potential—the P3 wave—may be related to memory functions and may arise from activity within the medial temporal lobe, especially the hippocampus. The latter idea was tested by means of epidural recordings of brain waves in monkeys. Responses to deviant auditory stimuli bore a close resemblance to P3 waves recorded from human subjects under comparable conditions. Monkeys with bilateral lesions of the medial temporal lobe still produced P3-like brain waves, which indicates that medial temporal brain structures are not critical for their generation. Perceptual and cognitive events in humans are reliably associated with measures of brain electrical activity recorded noninvasively from the scalp and extracted from the electroencephalogram using signal averaging. These event-related brain potentials (ERPs) provide a way to study neural mechanisms of information processing (Donchin, 1984; Gaillard R Galambos& Hillyard, 1981; Hillyard &Kutas, 1983).