Biomedical subjects

J C Gewirtz

Publications and source records attributed to J C Gewirtz.

18 recordsLinked to original sources

PubMed2006

Double dissociation in the neural substrates of acute opiate dependence as measured by withdrawal-potentiated startle.

The basolateral amygdala and portions of the "extended" amygdala (i.e. central nucleus of the amygdala, bed nucleus of the stria terminalis and shell of the nucleus accumbens) have been implicated in the aversive aspects of withdrawal from chronic opiate administration. Given that similar withdrawal signs are observed following a single opiate exposure, these structures may also play a role in "acute opiate dependence." In the current study, drug-naïve rats underwent naloxone-precipitated withdrawal from acute morphine (10 mg/kg) exposure on two successive days. On either the first or second day of testing, the basolateral amygdala, central nucleus of the amygdala, bed nucleus of the stria terminalis, or nucleus accumbens was temporarily inactivated immediately prior to naloxone injection by microinfusion of the glutamatergic alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo(f)quinoxaline-7-sulfonamide (3 microg/0.5 microl). On the first day, inactivation of the basolateral amygdala, central nucleus of the amygdala, or bed nucleus of the stria terminalis, but not the nucleus accumbens blocked withdrawal-potentiated startle, a behavioral measure of the anxiogenic effects of withdrawal. On the second day, inactivation of the nucleus accumbens, but not the basolateral amygdala, central nucleus of the amygdala, or bed nucleus of the stria terminalis disrupted the withdrawal effect. Effects of structural inactivations on withdrawal-potentiated startle were not influenced by differences in withdrawal severity on the two days of testing. A fear-potentiated startle procedure provided functional confirmation of correct cannulae placement in basolateral amygdale- and central nucleus of the amygdala-implanted animals. Our findings indicate a double dissociation in the neural substrates of withdrawal-potentiated startle following a first versus second morphine exposure, and may reflect a reorganization of the neural circuitry underlying the expression of withdrawal-induced negative affect during the earliest stages of opiate dependence.

Acoustic Stimulation↗

PubMed2001

Stress differentially regulates synaptophysin and synaptotagmin expression in hippocampus.

BACKGROUND: In view of the effects of stress on synaptic plasticity, the regulation of synaptophysin and synaptotagmin expression by immobilization was analyzed by in situ hybridization. METHODS: Rats were exposed to immobilization stress, which induced typical behavioral alterations, such as reduced locomotor activity after stress exposure. Determination of mRNA levels of the integral synaptic vesicle proteins was performed immediately after acute or chronic immobilization. RESULTS: The results demonstrate that stress exposure leads to reduced expression of synaptophysin but increased expression of synaptotagmin in the hippocampus. CONCLUSIONS: This rapid and differential regulation of synaptic vesicle proteins could be responsible for some of the morphological, biochemical, and behavioral changes observed after stress exposure. These changes may be relevant to such clinical disorders as psychoses, depression, and posttraumatic stress disorder that are sensitive to stress and involve changes in neural and synaptic plasticity.

Animals↗

PubMed2001

A major role for thalamocortical afferents in serotonergic hallucinogen receptor function in the rat neocortex.

Activation of 5-hydroxytryptamine(2A) (5-HT(2A)) receptors by hallucinogenic drugs is thought to mediate many psychotomimetic effects including changes in affect, cognition and perception. Conversely, blockade of 5-HT(2A) receptors may mediate therapeutic effects of many atypical antidepressant and antipsychotic drugs. The purpose of the present study was to determine the source of subcortical glutamatergic afferents, which would project widely throughout the anterior-posterior axis of the rat brain to the apical dendrites of layer V pyramidal cells of the medial prefrontal cortex, from which serotonin induces transmitter release via activation of 5-HT(2A) receptors. Fiber-sparing chemical lesions of the medial thalamus selectively decreased the frequency of serotonin-induced excitatory postsynaptic currents recorded from layer V pyramidal cells in the prelimbic region of the medial prefrontal cortex by 60%. In contrast, large bilateral lesions of the amygdala did not alter the serotonin response. These thalamic lesions significantly decreased the amount of binding to either mu-opioid or metabotropic glutamate 2/3 receptors in the prelimbic region of the medial prefrontal cortex as expected from previous evidence that these agonists for these receptors suppress serotonin-induced excitatory postsynaptic currents by a presynaptic mechanism. Surprisingly, the amount of specific binding to cortical 5-HT(2A) receptors was significantly increased by the medial thalamic lesions. Thus, these experiments demonstrate that activation of cortical 5-HT(2A) receptors modulates transmitter release from thalamocortical terminals. Unexpectedly, lesioning the thalamocortical terminals also alters 5-HT(2A) receptor binding in the prefrontal cortex. These findings are of interest with respect to understanding therapeutic effects of antidepressant/antipsychotic drugs and the known behavioral effects of thalamic lesions in humans.

Amygdala↗

PubMed2000

Is the hippocampus necessary for contextual fear conditioning?

The hippocampus is widely believed to be essential for learning about the context in which conditioning occurs. This view is based primarily on evidence that lesions of the dorsal hippocampus disrupt freezing to contextual cues after fear conditioning. However, lesions that disrupt freezing produce no effect on fear-potentiated startle, a second measure of contextual fear. Moreover, hippocampal lesions also do not disrupt the contextual 'blocking' phenomenon, which provides an indirect measure of contextual fear. In these paradigms, at least, it appears that hippocampal lesions disrupt the expression of freezing, rather than contextual fear itself. This interpretation is supported by the finding that rats showing preserved contextual blocking after hippocampal lesions show deficits not only in contextual freezing, but also in unconditioned freezing. These findings are consistent with a growing body of data from other conditioning paradigms that contextual learning is spared after lesions of the dorsal hippocampus. Nonetheless, there remain some reports of impaired contextual fear conditioning after hippocampal lesions that cannot be attributed easily to a disruption of freezing. Thus, it is concluded that the hippocampus may be involved in contextual learning under certain--as yet, unspecified--circumstances, but is not critical for contextual learning in general.

Animals↗

PubMed2000

Behavioral evidence for interactions between a hallucinogenic drug and group II metabotropic glutamate receptors.

Recent electrophysiological studies in our laboratory have demonstrated a physiological interaction between 5-HT(2A) and metabotropic glutamate2/3 (mGlu2/3) receptors in the medial prefrontal cortex. Several behavioral studies have found that phenethylamine hallucinogens with partial agonist activity at 5-HT(2A) receptors induce head shakes when directly administered into the medial prefrontal cortex. The purpose of the present experiments was to examine whether an interaction occurs between mGlu2/3 and 5-HT(2A) receptors on a behavioral level using head shakes induced by phenethylamine hallucinogens as a model of 5-HT(2A) receptor activation. Administration of the mGlu2/3 agonist LY354740 (0.3-10 mg/kg, ip) suppressed head shakes induced by the phenethylamine hallucinogen 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Conversely, administration of the mGlu2/3 antagonist LY341495 (1 mg/kg, ip) enhanced the frequency of DOI-induced head shakes. Taken together, these results raise the possibility that the psychomimetic properties of hallucinogenic drugs may be mediated in part, via increased glutamate release following activation of 5-HT(2A) receptors.

Amino Acids↗

PubMed2000

Disruption of contextual freezing, but not contextual blocking of fear-potentiated startle, after lesions of the dorsal hippocampus.

The role of the dorsal hippocampus in contextual fear conditioning was investigated with a contextual blocking paradigm. In Experiment 1, rats were given pairings of a light conditioned stimulus (CS) and footshock after preexposure either to footshock or to the context alone. The group preexposed to footshock showed poorer fear conditioning to the light CS, as measured by the fear-potentiated startle reflex. In Experiment 2, a group preexposed to footshock in the same context showed poorer fear conditioning to the light CS than did a group preexposed to footshock in a different context, indicating contextual blocking of fear-potentiated startle. In Experiment 3, lesions of the dorsal hippocampus had no effect on contextual blocking, even though contextual freezing was disrupted. The sparing of contextual blocking indicated that contextual memory was intact following hippocampal lesions, despite the disruption of contextual freezing.

Animals↗

PubMed2000

Genome polymorphism and alcoholism.

Different gene variants have been identified as risk or protective factors in alcoholism. The genes coding for dopamine receptors, serotonin transporters, and dehydrogenases represent susceptibility loci for addictive behaviour. However, alcoholism represents a complex psychiatric symptomatology which is caused by multiple factors, both genetic and environmental. Furthermore, there are probably different subtypes of alcoholism each with a distinct pathophysiology, and thus a different genetic background. Genetic research can help to identify such subtypes, which may require different therapeutic approaches. However, gene polymorphisms are not only responsible for a predisposition to alcoholism, but also for personality traits which influence the likelihood of developing addictive behaviour. Moreover, genetic polymorphisms are probably involved in the way an individual responds to treatment. Also, the severity of secondary diseases resulting from chronic alcohol uptake may depend on the genetic makeup of an individual. New treatment strategies focusing on genes contributing towards drug and alcohol dependence (such as gene therapy) are already under examination in animal models. However, further research is required before these developments will considerably change today's clinical handling of alcoholism.

Alcoholism↗

PubMed1999

Polymorphisms of the human apolipoprotein E promoter and bleomycin hydrolase gene: risk factors for Alzheimer's dementia?

In addition to the apolipoprotein E (ApoE) tri-allele polymorphism, genetic variants of the apolipoprotein E promoter (-491A/T) and the bleomycin hydrolase (BH-PEN) gene have also been proposed as genetic risk factors for Alzheimer's dementia (AD). Since reports about the relevance of these polymorphisms for the pathogenesis of AD have been contradictory, we performed an association study with some modifications. First, the control group in this study was made up of non-demented psychiatric inpatients, rather than healthy subjects. This procedure allows the specificity of the relationship between a given genotype and AD (as opposed to other psychiatric disorders) to be determined. Second, as an alternative to preexisting relatively time consuming techniques, BH-PEN polymorphism was determined using a simplified method based on PCR genotyping. We found a significant linkage disequilibrium between the -491A/T and ApoE polymorphisms. However, no direct association was observed between the -491A/T or BH-PEN polymorphism and AD.

Alleles↗

PubMed1998

Lesions of the bed nucleus of the stria terminalis block sensitization of the acoustic startle reflex produced by repeated stress, but not fear-potentiated startle.

1. The effects of lesions of the bed nucleus of the stria terminalis (BST) on the acquisition of conditioned fear were examined. In Experiment 1, BST lesions did not block acquisition of fear-potentiated startle to an explicit visual conditioned stimulus (CS) over 20 days of training. However, BST lesions blocked a gradual elevation in baseline startle also seen over the course of training. 2. The gradual increase in baseline startle was replicated in Experiment 2 without the presence of an explicit CS, using unoperated subjects. Experiment 2 showed that the elevation was due to repetitive exposure to shock, because unshocked control subjects did not show any elevation over sessions. 3. In Experiment 3, lesions of the BST did not disrupt rapid sensitization of the startle reflex by footshock, showing that different neural substrates underlie sensitization of startle by acute and chronic exposure to footshock. 4. These data indicate that the BST, despite its anatomical continuity with the amygdala, is not critically involved in the acquisition of conditioned fear to an explicit CS. Nevertheless, the BST is involved in mediating a stress-induced elevation in the startle reflex. This suggests that the BST and the CeA, which constitute part of the "extended amygdala" have complementary roles in responses to stress.

Acoustic Stimulation↗

PubMed1998

Modulation of the acquisition of the rabbit eyeblink conditioned response by conditioned contextual stimuli.

Three experiments were conducted to ask if conditioned emotional responses (CERs) controlled by contextual cues modulate the acquisition of eyelid conditioned responses (CRs) to discrete conditioned stimuli (CSs). Experiment 1 showed that 30-s auditory stimuli that were paired with aversive shocks to one paraorbital region or the other controlled discriminated CERs, as measured by potentiation of a startle response. In Experiments 2 and 3, similarly trained 30-s stimuli served as contexts in which 1.050-ms CSs were paired with a paraorbital unconditioned stimulus (US). Reinforced contexts both impaired (Experiments 2A and 2B) and facilitated (Experiment 3B) acquisition of the eyeblink CR, depending on the locus of the USs involved. The data are consistent with the interpretation that CERs controlled by contextual cues facilitate CR acquisition, but do so in the face of blocking effects of CR tendencies also conditioned to the contextual cues.

Animals↗

PubMed1997

Evidence of contextual fear after lesions of the hippocampus: a disruption of freezing but not fear-potentiated startle.

The roles of the dorsal hippocampus and the central nucleus of the amygdala in the expression of contextual fear were assessed using two measures of conditioned fear: freezing and fear-potentiated startle. A discriminable context conditioning paradigm was developed that demonstrated both conditioned freezing and fear-potentiated startle in a context paired previously with foot shock, relative to a context in which foot shock had never been presented. Post-training lesions of the central nucleus of the amygdala completely blocked both contextual freezing and fear-potentiated startle. Post-training lesions of the dorsal hippocampus attenuated contextual freezing, consistent with previous reports in the literature; however, these same lesions had no effect on fear-potentiated startle, suggesting preserved contextual fear. These results suggest that lesions of the hippocampus disrupt the freezing response but not contextual fear itself.

Acoustic Stimulation↗

PubMed1997

Second-order fear conditioning prevented by blocking NMDA receptors in amygdala.

Antagonists of NMDA (N-methyl-D-aspartate)-type glutamate receptors disrupt several forms of learning. Although this might indicate that NMDA-receptor-mediated processes are critical for synaptic plasticity, there may be other mechanisms by which NMDA-receptor antagonism could interfere with learning. For instance, fear conditioning would be blocked by microinfusion of the NMDA-receptor antagonist AP5 (D,L-2-amino-5-phosphonovalerate) into the basolateral amygdala if AP5 inhibited routine synaptic transmission, thereby reducing the ability of stimuli to activate amygdala neurons. In second-order fear conditioning, the reinforcer is a fear-eliciting conditioned stimulus rather than an unconditioned stimulus. Expression of conditioned fear is amygdala-dependent and so provides a behavioural assessment of the ability of the reinforcer to activate amygdala neurons in the presence of AP5. We report here that intra-amygdala AP5 actually enhances expression of conditioned fear to the conditioned stimulus that provides the reinforcement signal for second-order conditioning. Nevertheless, acquisition of second-order fear conditioning is completely blocked. Our findings strongly support the view that NMDA receptors are critically involved in synaptic plasticity.

2-Amino-5-phosphonovalerate↗

PubMed1997

Normal conditioned inhibition and extinction of freezing and fear-potentiated startle following electrolytic lesions of medical prefrontal cortex in rats.

The authors investigated the role of medial prefrontal cortex (mPFC) in the inhibition of conditioned fear in rats using both Pavlovian extinction and conditioned inhibition paradigms. In Experiment 1, lesions of ventral mPFC did not interfere with conditioned inhibition of the fear-potentiated startle response. In Experiment 2, lesions made after acquisition of fear conditioning did not retard extinction of fear to a visual conditioned stimulus (CS) and did not impair "reinstatement" of fear after unsignaled presentations of the unconditioned stimulus. In Experiment 3, lesions made before fear conditioning did not retard extinction of fear-potentiated startle or freezing to an auditory CS. In both Experiments 2 and 3, extinction of fear to contextual cues was also unaffected by the lesions. These results indicate that ventral mPFC is not essential for the inhibition of fear under a variety of circumstances.

Acoustic Stimulation↗

PubMed1995

Habituation of prepulse inhibition of the startle reflex using an auditory prepulse close to background noise.

This study examined whether prepulse inhibition habituates with repeated presentation of the prepulse alone. Prepulse inhibition was determined by measuring the decrement in the startle response when the acoustic startle-eliciting stimulus was preceded by an auditory prepulse. Rats received repetitive exposures of the same auditory prepulse alone (experimental condition) and of a visual prepulse alone (control condition). To reduce habituation of startle itself and the possible dishabituating influence the startle stimulus might have on habituation of prepulse inhibition, startle stimulus presentations were infrequently interspersed among a much larger number of prepulse-alone presentations. Stimulus-specific habituation of prepulse inhibition occurred using an auditory prepulse 2.5 dB, but not 13 dB, above background noise. Implications are discussed for the role of prepulse inhibition in sensory gating.

Animals↗

PubMed1995

Latent inhibition in humans: data, theory, and implications for schizophrenia.

Learning about the consequences of a stimulus is retarded if that stimulus has been experienced without reinforcement. A literature review of this latent inhibition (LI) effect indicates that LI is similar in human and other species, although in adult humans it often requires a masking or distracter task. The discrepancy in conditions for producing LI can be accounted for by developmental differences in the automatic processing of unattended stimuli. In adults, automatic processes are subject to a controlled information-processing override. Masking prevents controlled processing of the preexposed stimuli so that they remain unattended. The role of masking in attenuating LI in schizotypal/schizophrenic groups is assessed. It is proposed that schizophrenia is related to an inability to use occasion-setting properties of context or to switch from controlled to automatic processing of inconsequential events.

Adult↗

PubMed1993

The role of gender-related information and self-endorsement of traits in preadolescents' inferences and judgments.

The major purpose of this study was to examine the effects of a target child's gender typicality on different aspects of preadolescents' inferences and judgments. The secondary purpose of the study was to investigate the relation between children's self-endorsement of traits and their inferences and judgments. Fifth and sixth graders were shown a video film, portraying a child playing either a gender-appropriate game with members of the same sex or a gender-inappropriate game with members of the other sex. In addition, subjects completed an adapted version of the BSRI and were categorized into sex-typed, androgynous, and undifferentiated subjects. Subjects made a number of different types of judgments and inferences about the target, including inferences about traits, popularity, choice of gift and name, and willingness to engage in activities with the target. All types of inferences and judgments were affected by the variations in the targets' gender-related behaviors, whereas self-endorsement of traits was not related to the inferences and judgments. The results suggest that the gender typicality of the target behavior is salient to preadolescents, regardless of their sex-role orientation.

Adolescent↗

PubMedDate not supplied

Application of Pavlovian higher-order conditioning to the analysis of the neural substrates of fear conditioning.

In Pavlovian first-order conditioning, a conditioned response is acquired by pairing a neutral stimulus (S1) with a stimulus that has innate motivational value. In higher-order conditioning, a neutral stimulus (S2) is paired with S1 either after (second-order conditioning) or before (sensory preconditioning) first-order conditioning has been acquired. Thus, in higher-order conditioning the motivational value of the reinforcer is acquired rather than innate. This review describes some of the potential uses of higher-order conditioning in investigating the neural substrates of fearful memories. First, because in second-order fear conditioning S2 is not paired directly with a painful stimulus, any effect of a treatment on the acquisition of fear cannot be attributed to the treatment's possible effects on transmission of nociceptive information. Second, higher-order conditioning provides opportunities for analyzing where and how different types of events, or different aspects of the same events, are represented in the brain.

Animals↗

PubMedDate not supplied

Using pavlovian higher-order conditioning paradigms to investigate the neural substrates of emotional learning and memory.

In first-order Pavlovian conditioning, learning is acquired by pairing a conditioned stimulus (CS) with an intrinsically motivating unconditioned stimulus (US; e.g., food or shock). In higher-order Pavlovian conditioning (sensory preconditioning and second-order conditioning), the CS is paired with a stimulus that has motivational value that is acquired rather than intrinsic. This review describes some of the ways higher-order conditioning paradigms can be used to elucidate substrates of learning and memory, primarily focusing on fear conditioning. First-order conditioning, second-order conditioning, and sensory preconditioning allow for the controlled demonstration of three distinct forms of memory, the neural substrates of which can thus be analyzed. Higher-order conditioning phenomena allow one to distinguish more precisely between processes involved in transmission of sensory or motor information and processes involved in the plasticity underlying learning. Finally, higher-order conditioning paradigms may also allow one to distinguish between processes involved in behavioral expression of memory retrieval versus processes involved in memory retrieval itself.

Animals↗