Role of entorhinal cortical plasticity in spatial and contextual memory

It is well accepted that the hippocampus (HIP) is important for spatial and contextual memories, however, it is not clear if the entorhinal cortex (EC), the main input/output structure for the hippocampus, is also necessary for memory storage. Damage to the EC in humans results in memory deficits. However, animal studies report conflicting results on whether the EC is necessary for spatial and contextual memory. Memory consolidation requires gene expression and protein synthesis, mediated by signaling cascades and transcription factors. Extracellular-signal regulated kinase (ERK) cascade activity is necessary for long-term memory in several tasks, including those that test spatial and contextual memory. In this work, we explore the role of ERK-mediated plasticity in the EC on spatial and contextual memory. ^ To evaluate this role, post-training infusions of reversible pharmacological inhibitors specific for the ERK cascade that do not affect normal neuronal activity were targeted directly to the EC of awake, behaving animals. This technique provides spatial and temporal control over the inhibition of the ERK cascade without affecting performance during training or testing. Using the Morris water maze to study spatial memory, we found that ERK inhibition in the EC resulted in long-term memory deficits consistent with a loss of spatial strategy information. When animals were allowed to learn and consolidate a spatial strategy for solving the task prior to training and ERK inhibition, the deficit was alleviated. To study contextual memory, we trained animals in a cued fear-conditioning task and saw an increase in the activation of ERK in the EC 90 minutes following training. ERK inhibition in the EC over this time point, but not at an earlier time point, resulted in increased freezing to the context, but not to the tone, during a 48-hour retention test. In addition, animals froze maximally at the time the shock was given during training; similar to naïve animals receiving additional training, suggesting that ERK-mediated plasticity in the EC normally suppresses the temporal nature of the freezing response. These findings demonstrate that plasticity in the EC is necessary for both spatial and contextual memory, specifically in the retention of behavioral strategies. ^

Extending in vitro conditioning in Aplysia to analyze operant and classical processes in the same preparation.

Operant and classical conditioning are major processes shaping behavioral responses in all animals. Although the understanding of the mechanisms of classical conditioning has expanded significantly, the understanding of the mechanisms of operant conditioning is more limited. Recent developments in Aplysia are helping to narrow the gap in the level of understanding between operant and classical conditioning, and have raised the possibility of studying the neuronal processes underlying the interaction of operant and classical components in a relatively complex learning task. In the present study, we describe a first step toward realizing this goal, by developing a single in vitro preparation in which both operant and classical conditioning can be studied concurrently. The new paradigm reproduced previously published results, even under more conservative and homogenous selection criteria and tonic stimulation regime. Moreover, the observed learning was resistant to delay, shortening, and signaling of reinforcement.

In vitro analog of classical conditioning of feeding behavior in aplysia.

The feeding behavior of Aplysia californica can be classically conditioned using tactile stimulation of the lips as a conditioned stimulus (CS) and food as an unconditioned stimulus (US). Moreover, several neural correlates of classical conditioning have been identified. The present study extended previous work by developing an in vitro analog of classical conditioning and by investigating pairing-specific changes in neuronal and synaptic properties. The preparation consisted of the isolated cerebral and buccal ganglia. Electrical stimulation of a lip nerve (AT4) and a branch of the esophageal nerve (En2) served as the CS and US, respectively. Three protocols were used: paired, unpaired, and US alone. Only the paired protocol produced a significant increase in CS-evoked fictive feeding. At the cellular level, classical conditioning enhanced the magnitude of the CS-evoked synaptic input to pattern-initiating neuron B31/32. In addition, paired training enhanced both the magnitude of the CS-evoked synaptic input and the CS-evoked spike activity in command-like neuron CBI-2. The in vitro analog of classical conditioning reproduced all of the cellular changes that previously were identified following behavioral conditioning and has led to the identification of several new learning-related neural changes. In addition, the pairing-specific enhancement of the CS response in CBI-2 indicates that some aspects of associative plasticity may occur at the level of the cerebral sensory neurons.

Addressing Obesity: Fear of Crime, Perceptions of Disorder and Disaparities in Child and Adolescent Use of Public Parks

Abstract The objectives of this study were: 1) To determine factors which inhibit and facilitate child and adolescent use of outdoor spaces for healthy physical activity by race and ethnicity in four Houston communities and 2) To propose guidelines for encouraging and maintaining child and adolescent outdoor physical activity. Using local health data and Houston Police Department crime statistics, four communities were identified for the study that had the highest concentration of crime and the racial/ ethnic groups of interest. The researchers then identified public parks in the communities. At least two parks were observed in each of the four communities from 2010 to 2011 during spring, summer, fall and winter. The parks were observed for use by children and adolescents and to describe the condition of the park spaces. The communities were Alief (Asian), Sunnyside (Black), Eldridge- West Oaks (White) and Northside- Northline (Hispanic). Observations were made at varying hours of both day and night, weekdays and weekends. Photographs were taken and the condition of the spaces noted in detail. One hundred and twenty persons, 18 years and over, using the spaces or otherwise in these communities were conveniently sampled and interviewed about their health and the extent to which they, or any children or adolescents under their care, used the outdoor spaces of interest. Data were analyzed qualitatively and with basic descriptive statistics. The photographs, journal notes and observation notes of all investigators and key personnel were analyzed. Interview data were also coded to identify patterns and themes in the responses. The findings indicate disparities in the quality and quantity of park equipment and the maintenance of the areas. Where perceptions of disorder were described, there was often visible evidence to support the perceptions. In many cases, residents' perceptions of crime were corroborated by police data. While interview reports did not seem to support the expectation that the condition of the parks was a significant deterrent to their use by children and adolescents, the condition of the parks might be said to limit the extent of that use. Specific reports of disorder that inhibited use included hearing gunfire, seeing drug dependent homeless persons and/or suspected prostitutes in an area.

Cerebellar cortex involvement in classical eyelid conditioning

A model for cerebellar involvement in motor learning was tested using classical eyelid conditioning in the rabbit. Briefly, we assume that modifications of the strength of granule cell synapses at Purkinje cells in the cerebellar cortex and mossy fiber (MF) synapses at cerebellar interpositus nuclei are responsible for the acquisition, adaptively-timed expression, and extinction of conditioned eyelid responses (CRs). A corollary of these assumptions is that the cerebellar cortex is necessary for acquisition and extinction. This model also suggests a mechanism whereby the cerebellar cortex can discriminate different times during a conditioned stimulus (CS) and thus mediate the learned timing of CRs. Therefore, experiments were done to determine the role of the cerebellar cortex in the timing, extinction, and acquisition of CRs. Lesions of the cerebellar cortex that included the anterior lobe disrupted the learned timing of CRs such that they occurred at extremely short latencies. Stimulation of MFs in the middle cerebellar peduncle as the CS could support differently timed CRs in the same animal. These data indicate that synaptic plasticity in the cerebellar cortex mediates the learned timing of CRs. These short-latency CRs which resulted from anterior lobe damage did not extinguish, while CRs in animals receiving lesions which did not include the anterior lobe extinguished normally. Preliminary data suggests that lesions of the anterior lobe which produce short-latency responses prevent the acquisition of CRs to a novel CS. These findings indicate that the anterior lobe of cerebellar cortex is necessary for eyelid conditioning. The involvement of the anterior lobe in eyelid conditioning has not been previously reported, however, the anterior lobe has generally been spared in lesion studies examining cerebellar cortex involvement in eyelid conditioning due to its relatively inaccessible location. The observation that the anterior lobe of the cerebellar cortex is not always required for the basic expression of CRs, but is necessary for response timing, extinction, and acquisition, is consistent with the hypothesis that eyelid conditioning can involve plasticity in both the cerebellar cortex and interpositus nucleus and that plasticity in the nucleus is controlled by Purkinje cell activity. ^

Characterization of the interactions between two sites of plasticity engaged during eyelid conditioning

Here, we investigate the involvement of two sites of plasticity in the learning and expression of a simple associative motor behavior—the classically conditioned eyelid response. While previous studies clearly demonstrate that lesions of the anterior interpositus nucleus of the cerebellum abolish learned responses and prevent subsequent learning, studies investigating the effects of lesions of the cerebellar cortex on learning and retention have produced discrepant results. We complement ablative lesion studies of the cortex with the use of reversible, pharmacological blockade of cerebellar cortical transmission to investigate the role of the cerebellar cortex in eyelid conditioning. We demonstrate that both pharmacological blockade as well as focused ablative lesions of the cortex abolish timed responses and unmask responses with a fixed, short latency that are not displayed by the intact animal. Pharmacological blockade of cerebellar cortex output at various stages of acquisition and extinction reveals appropriate, learning dependent changes in the amplitude and probability of short latency responses during training. Acquisition of both short latency as well as timed responses is prevented by ablative lesions of the anterior lobe of the cerebellar cortex. These convergent results from technically distinct methods of removing the influence of the cerebellar cortex from conditioned behavior are consistent with the proposal that (1) eyelid conditioning engages two cerebellar sites of plasticity-one in the cortex and one in the anterior interpositus nucleus, (2) plasticity in the cerebellar cortex is necessary for proper response timing, (3) plasticity in the nucleus mediates the short latency responses unmasked by lesions of the cerebellar cortex, and (4) cerebellar cortical output is necessary for the induction of plasticity in the nucleus. ^

Behavioral and cellular analysis of classical conditioning of feeding behavior in Aplysia

In classical conditioning, an associative form of learning, animals learn to associate two stimuli. Cellular and molecular mechanisms for the induction and consolidation of associative learning and memory at the level of single cells and synaptic connections have been studied in both vertebrate and invertebrate animals. The majority of studies, however, relied on aversive stimuli to induce learning. This bias may limit the extent to which identified mechanisms generalize to other forms of associative learning and memory, such as appetitive forms. The goal of the present study was to develop a classical conditioning procedure for the marine mollusk Aplysia californica using appetitive reinforcement, and to analyze associative learning using behavioral and electrophysiological techniques. ^ Using tactile stimulation of the lips as the conditional stimulus (CS) and food as the unconditional stimulus (US) a training protocol was developed that reliably induced classical conditioning of feeding behavior. Memory persisted for at least 24 hours. The gross organization of reinforcement-mediating pathways was analyzed in additional behavioral experiments. Moreover, neurophysiological correlates of classical conditioning were identified and characterized in an in vitro preparation containing the circuitry for feeding behavior. In vitro stimulation of a nerve (AT4) that may mediate the CS during training, resulted in a greater number of buccal motor patterns (BMPs) in brains from conditioned animals, as compared to control animals. The majority of these BMPs were ingestion-like, consistent with the increased number of bites in response to the CS after classical conditioning. Moreover, classical conditioning correlated with increased excitatory synaptic input to BMP-initiating neuron B31/32, in response to stimulation of AT 4, as compared to controls. The expression of the correlates of classical conditioning identified in this study was specific to stimulation of AT 4, which is consistent the stimulus specificity that is characteristic for classical conditioning. ^ The identification of cellular correlates of classical conditioning documented here provides the basis for future, more detailed analyses of an appetitive form of associative learning and memory, that may extend the working knowledge of the cellular and molecular mechanisms for associative plasticity in general. ^

Learning in the cerebellar nucleus is necessary for acquisition of Pavlovian eyelid conditioning

The cumulative work presented here supports the hypothesis that plasticity in the cerebellar cortex and cerebellar nuclei mediates a simple associative form of motor teaming-Pavlovian eyelid conditioning. It was previously demonstrated that focal ablative lesions of cerebellar anterior lobe or pharmacological block of the cerebellar cortex output disrupted the timing of the conditioned eyeblink response, unmasking a response with a relatively fixed and very short latency to onset. The results of this thesis demonstrate that the short-latency responses are due to associative learning. Unpaired training does not support the acquisition of short-latency responses while the rate of acquisition of short-latency responses during paired training is approximately the same as that of timed conditioned responses. The acquisition of short-latency responses is dependent on an intact cerebellar cortex. Both ablative lesions of the cerebellar cortex and inactivation of cerebellar cortex output with picrotoxin block the acquisition of short-latency responses. However, once the short-latency responses are acquired neither disconnection of cerebellar cortex nor inactivation of the cerebellar nucleus block reacquisition. The results are consistent with the proposal that plasticity in the cerebellar cortex is necessary for learning the timing of conditioned responses, plasticity in the interpositus nucleus mediates the short latency responses, and cerebellar cortical output and mossy fiber input are necessary for the acquisition of short latency responses. ^

Cellular mechanisms of operant and classical conditioning

The ability to associate a predictive stimulus with a subsequent salient event (i.e., classical conditioning) and the ability to associate an expressed behavior with the consequences (i.e., operant conditioning) allow for a predictive understanding of a changing environment. Although they are operationally distinct, there has been considerable debate whether at some fundamental level classical and operant conditioning are mechanistically distinct or similar. Feeding behavior of Aplysia (i.e., biting) was chosen as the model system and was successfully conditioned with appetitive forms of both operant and classical conditioning. The neuronal circuitry responsible for feeding is well understood and is suitable for cellular analyses, thus providing for a mechanistic comparison between these two forms of associative learning. ^ Neuron B51 is part of the feeding circuitry of Aplysia and is critical for the expression of ingestive behaviors. B51 also is a locus of plasticity following both operant and classical conditioning. Both in vivo and in vitro operant conditioning increased the input resistance and the excitability of B51. No pairing-specific changes in the input resistance were observed following both in vivo and in vitro classical conditioning. However, classical conditioning decreased the excitability of B51. Thus, both operant and classical conditioning modified the threshold level for activation of neuron B51, but in opposite directions, revealing key differences in the cellular mechanisms underlying these two forms of associative learning. ^ Next, the cellular mechanisms underlying operant conditioning were investigated in more detail using a single-cell analogue. The single-cell analogue successfully recapitulated the previous in vivo and in vitro operant conditioning results by increasing the input resistance and the excitability of B51. Both PKA and PKC were necessary for operant conditioning. Dopamine appears to be the transmitter mediating the reinforcement signal in this form of conditioning. A D1 dopamine receptor antibody revealed that the D1receptor localizes to the axon hillock, which is also the region that gives the strongest response when iontophoresing dopamine. ^ The studies presented herein, thus, provide for a greater understanding of the mechanisms underlying both of these forms of associative learning and demonstrate that they likely operate through distinct cellular mechanisms. ^

Forebrain-cerebellum interactions revealed by trace eyelid conditioning

While it is commonly assumed that brain systems receive and process information from other brain systems, there are few examples of tractable behaviors that allow such interactions to be studied. With the experiments presented in this dissertation we provide evidence that trace eyelid conditioning, a simple form of associative learning, is mediated by cerebellar learning in response to the output of persistent neural activity in the prefrontal cortex (PFC) and thus may be useful in analyses of PFC-cerebellar interactions. In a series of stimulation and reversible inactivation experiments we provide evidence that trace eyelid conditioning is mediated by cerebellar learning in response to a learned forebrain-driven input. Specifically, we provide evidence that this input is driven by the medial PFC and persists through the stimulus free trace interval of trace eyelid conditioning. In the next set of experiments we show that directly presenting the cerebellum with a pattern of input that mimics the classic persistent activity of PFC neurons reconstitutes trace eyelid conditioning, as assessed by a number of stringent tests. Finally, in set of reversible inactivation experiments, we provide evidence that bidirectional learning during trace eyelid conditioning involves the omission of the persistent, PFC-driven input that the cerebellum learns and responds to during trace eyelid conditioning. Given that persistent activity in PFC is often associated with working memory, these experiments suggest that trace eyelid conditioning may be useful in analyses of working memory mechanisms, cerebellar information processing and their interaction. To facilitate future analyses, we conclude with a working hypothesis of forebrain-cerebellum interactions during trace eyelid conditioning that addresses how persistent activity in PFC is induced and how the cerebellum decodes and uses PFC-driven input. ^

Cross-culture perspectives on fear of HIV disease and AIDS in health care workers

Health care workers have been known to carry into the workplace a variety of judgmental and negative attitudes towards their patients. In no other area of patient care has this issue been more pronounced as in the management of patients with AIDS. Health care workers have refused to treat or manage patients with AIDS and have often treated them more harshly than identically described leukemia patients. Some health care institutions have simply refused to admit patients with AIDS and even recent applicants to medical colleges and schools of nursing have indicated a preference for schools in areas with low prevalence of HIV disease. Since the attitudes of health care workers do have significant consequences on patient management, this study was carried out to determine the differences in clinical practice in Nigeria and the United States of America as it relates to knowledge of a patient's HIV status, determine HIV prevalence and culture in each of the study sites and how they impact on infection control practices, determine the relationship between infection control practices and fear of AIDS, and also determine the predictors of safe infection control practices in each of the study sites.^ The study utilized the 38-item fear of AIDS scale and the measure of infection control questionnaire for its data. Questionnaires were administered to health care workers at the university teaching hospital sites of Houston, Texas and Calabar in Nigeria. Data was analyzed using a chi-square test, and where appropriate, a student t-tests to establish the demographic variables for each country. Factor analysis was done using principal components analysis followed by varimax rotation to simple structure. The subscale scores for each study site were compared using t-tests (separate variance estimates) and utilizing Bonferroni adjustments for number of tests. Finally, correlations were carried out between infection control procedures and fear of AIDS in each study site using Pearson-product moment correlation coefficients.^ The study revealed that there were five dimensions of the fear of AIDS in health care workers, namely fear of loss of control, fear of sex, fear of HIV infection through blood and illness, fear of death and medical interventions and fear of contact with out-groups. Fear of loss of control was the primary area of concern in the Nigerian health care workers whereas fear of HIV infection through blood and illness was the most important area of AIDS related feats in United States health care workers. The study also revealed that infection control precautions and practices in Nigeria were based more on normative and social pressures whereas it was based on knowledge of disease transmission, supervision and employee discipline in the United States, and thus stresses the need for focused educational programs in health care settings that emphasize universal precautions at all times and that are sensitive to the cultural nuances of that particular environment. ^