The influence of 17beta-oestradiol on corticotrophin-releasing hormone induced suppression of luteinising hormone pulses and the role of CRH in hypoglycaemic stress-induced suppression of pulsatile LH secretion in the female rat

Corticotrophin-releasing hormone (CRH) released during stress has been implicated in the disruption of the reproductive neuroendocrine axis, and 17beta-oestradiol (E2) has been shown to enhance stress-induced suppression of pulsatile gonadotrophin-releasing hormone (GnRH) and luteinising hormone (LH) release. The aims of the present study were to examine the role of CRH in hypoglycaemic stress-induced suppression of LH pulses, and to investigate the influence of E2 on the inhibitory effect of CRH on pulsatile LH secretion in the female rat. Suppression of LH pulses by insulin-induced hypoglycaemic (IIH) stress was completely prevented by intracerebroventricular (icv) administration of a CRH antagonist. Central administration of CRH (5 microg) resulted in an interruption of LH pulses in E2 treated animals, but had little or no effect in the absence of this gonadal steroid. These results provide evidence of a pivotal role for CRH in mediating the suppressive effect of IIH stress on pulsatile LH secretion in the female rat, and highlight a sensitising role for E2 in CRH-induced suppression of LH pulses.     

Hypoglycemia-induced suppression of luteinizing hormone (LH) secretion in intact female rhesus macaques: role of vasopressin and endogenous opioids

The first objective of this study was to determine whether insulin-induced hypoglycemia (IIH) inhibits LH secretion in unrestrained female macaques during the follicular phase of the menstrual cycle. There was a consistent inhibitory effect of hypoglycemia on LH secretion within 3 h in these females. This inhibition was likely an indirect effect since low glucose levels did not inhibit GnRH secretion from GT1-1 neurones in vitro. We next investigated whether administration of a vasopressin antagonist (AVPa) either alone, or with naloxone could reverse the IIH-induced inhibition of LH release. Females were studied in the follicular phase during 10 h periods with blood samples collected every 10 min. Experimental groups were IIH (n=6), IIH+AVPa (n=5) and IIH+AVPa+naloxone (n=4). The first 5 h of each study served as a control and hypoglycemia was then induced with insulin. The AVPa was given as a bolus (180 microg) just before the insulin and was followed by a continuous infusion (180 microg/h) for 5 h. Naloxone (5 mg/kg) was given with the AVPa and followed by a continuous infusion (5 mg/kg/h) for 5 h. In the IIH group, LH reached its lowest value 3-4 h after insulin. Neither AVPa nor AVPa+naloxone infusion reversed the inhibitory action of hypoglycemia on LH release. These data suggest that if there are inhibitory actions of vasopressin and endogenous opioids on GnRH release induced by hypoglycemia, they are not sufficient to explain the suppression of GnRH/LH release in intact female primates.     

The role of articulatory suppression in immediate false recognition

False memory for critical lures has been widely documented in long-term memory using the Deese/Roediger-McDermott paradigm. Recent evidence suggests that false memory effects can also be found in short-term memory (STM), supporting models that assume a strong relationship between short-term and long-term memory processes. However, no study has examined the role of articulatory suppression on immediate false memory, even though phono-articulatory factors are critically involved in STM performance and are an intrinsic part of all STM accounts. The current study proposes a novel paradigm to assess false memory effects in a STM task under both silent and articulatory suppression conditions. Using immediate serial recognition, in which participants had to judge whether two successive mixed lists of six associated and non-associated words were matched, we examined true recognition of matching lists and false recognition of mismatching lists comprising a critical lure or unrelated distractor in two experiments. Results from both experiments indicated reduced true recognition of matching lists and greater false serial recognition of mismatching lists comprising a critical lure under articulatory suppression relative to silence. These findings provide further support for some current models of verbal short-term memory, which posit a strong relationship between short-term and long-term memory processes.     

The role of articulatory suppression in immediate false recognition

False memory for critical lures has been widely documented in long-term memory using the Deese/Roediger-McDermott paradigm. Recent evidence suggests that false memory effects can also be found in short-term memory (STM), supporting models that assume a strong relationship between short-term and long-term memory processes. However, no study has examined the role of articulatory suppression on immediate false memory, even though phono-articulatory factors are critically involved in STM performance and are an intrinsic part of all STM accounts. The current study proposes a novel paradigm to assess false memory effects in a STM task under both silent and articulatory suppression conditions. Using immediate serial recognition, in which participants had to judge whether two successive mixed lists of six associated and non-associated words were matched, we examined true recognition of matching lists and false recognition of mismatching lists comprising a critical lure or unrelated distractor in two experiments. Results from both experiments indicated reduced true recognition of matching lists and greater false serial recognition of mismatching lists comprising a critical lure under articulatory suppression relative to silence. These findings provide further support for some current models of verbal short-term memory, which posit a strong relationship between short-term and long-term memory processes.     

The role of thought suppression in building mental blocks

This research examined the role of thought suppression in the formation of mental blocks. In Experiment 1, participants were asked to generate a series of creative associates for two target words after initially suppressing a word that was semantically related to one of the two target words. Participants produced fewer responses, and experienced a greater sensation of being mentally blocked, when attempting to produce associates for the target word that was semantically related to the suppressed word. In Experiment 2, participants either thought about or suppressed a series of words prior to completing a word fragment completion task. Each word either corresponded exactly to one of the word fragment solutions (target primes) or resembled one of the solutions but was slightly different in its orthographic properties (negative primes). Participants performed most poorly on the items for which they had initially suppressed negative primes.     

The role of the response-punishment contingency in the suppression of a positively-reinforced operant

Two experiments tested the prediction from current theories of punishment that a response-contingent procedure is superior to a comparable noncontingent procedure for the administration of punishment. Results demonstrated that the two procedures produced comparable contiguity effects and did not contain artifacts present in previous research. Three different measures of suppression corroborated the findings that more response suppression occurred in the contingent procedure. Results were shown to be stable across eight days of shock administration (Experiment 1), and three levels of shock intensity (Experiment 2). In both experiments, response suppression occurred during contingent shocks associated with shock at offset, as well as after conditioned stimulus (CS) offset. The contingent procedure was associated with more suppression during both of these periods and also longer runs of CSs with complete suppression. The relevance of the present findings to current theories of punishment was discussed.     

Evaluating the role of contingency in differentially reinforced tic suppression

The current study evaluated the effects of tokens delivered on differential reinforcement of zero-rate behavior (DRO) schedules or noncontingently on tic suppression in 4 children with tics. Tic frequency was lower in 3 of 4 children when tokens were delivered contingent on the absence of tics than when tokens were delivered noncontingently.     

The perils of double consciousness: The role of thought suppression in stereotype threat

The goal of the present research is to demonstrate, and then alleviate, the role of thought suppression in depressing women’s math performance under stereotype threat. We hypothesize that when taking a math test, women (but not men) attempt to suppress thoughts of the math-related gender stereotype. Suppression leads to underperformance when it uses up cognitive resources. In Study 1, women underperform on a math test and show postsuppressional rebound of the stereotype when cognitive resources are reduced. In Study 2, women suppress the stereotype after a math test begins, but show rebound when the test is complete. In Study 3, making the stereotype irrelevant to the test improves performance and reduces postsuppressional rebound. In Studies 4 and 5, we test a strategy women can use to make suppression easier, and show that it restores math performance. Theoretical and practical implications are discussed.     

Understanding alexithymia in female adolescents: The role of attachment style

Adults with alexithymia retrospectively report emotional difficulties with caregivers during childhood. However, the association between attachment style and alexithymic traits may be evident at an earlier stage than adulthood, i.e. during adolescence. Sixty school-based healthy females aged 9–18 years (mean 14.08, SD 2.71 years) participated in an Attachment Style Interview (ASI) and completed the Toronto Alexithymia Scale (TAS-20). Greater levels of alexithymia were exhibited by both anxious and avoidant insecurely attached groups compared to securely attached participants. Fear of separation (characteristic of anxious attachment style) predicted both overall alexithymia scores and the specific alexithymic trait of ‘difficulty identifying feelings’ (DIF). Constraints on closeness (an avoidant attachment attitude) predicted ‘difficulty describing feelings’ (DDF). Low felt attachment to primary caregiver was a predictor of ‘externally oriented thinking’ (EOT). These findings indicate that features of anxious and avoidant insecure attachment styles are differentially related to the separate facets of alexithymia in female adolescents. Specifically, the findings concerning fear of separation may reflect the adolescent struggle for autonomy and the resulting effects on the affect regulation system. Our results also suggest that the normative differentiation of the emotional and cognitive aspects of alexithymia may occur on a developmental trajectory.     

The role of response-contingent incentives in lithium chloride-mediated suppression of an operant response

Three experiments investigated what role a novel incentive plays in the development of operant response suppression mediated by lithium chloride. In all experiments animals were trained to press two levers under concurrent schedules of reinforcement. In Experiment 1 responding on one lever delivered a familiar incentive (food pellets), whereas responding on an alternative lever delivered a novel incentive (sucrose solution) prior to lithium chloride injections. If lithium was administered immediately after the instrumental session, the action associated with the novel, but not with the familiar, incentive was suppressed. By comparison, in a control group for which responding on both levers led to the familiar incentive, both actions were suppressed. Experiment 2 examined whether the novelty, rather than the sensory properties, of the incentive is crucial for observing performance suppression. It was found that animals familiarized with the “target” incentive were insensitive to aversion conditioning by lithium, in that there was no difference in response rates between the action that delivered the familiar incentive from that which earned the “target”. In contrast, if animals were unfamiliar with the “target” incentive at the time of aversion conditioning, they suppressed responding on the lever that was associated with the novel incentive but did not suppress responding on the lever associated with the familiar incentive. Experiment 3 investigated the mechanism underlying instrumental performance suppression. After the completion of concurrent lever press training, novel sucrose was introduced in conjunction with the pellets for responding on one lever; responding on the other lever continued to deliver only familiar pellets. Lithium injections were then administered either immediately following the sessions or several hours after the sessions. It was found that the rate of responding on the lever associated with the contingent delivery of sucrose was suppressed below that of the pellet-alone action. By comparison, if lithium injections were administered several hours following the session, an elevation in responding on the sucrose-plus-pellet lever was observed. The outcomes of all three experiments demonstrate not only that the novelty of an incentive is important in obtaining performance suppression, but also that a novel incentive can punish instrumental responding if it has been associated with toxicosis.     

Post-trial stimulation and the acquisition of conditioned suppression in the rat

Three experiments investigated the effect of post-trial stimulation on conditioning. Rats were trained in a conditioned suppression procedure in which only half of the CS presentations were followed immediately by a shock reinforcer. Presenting a second, post-trial, shock 8 s after the end of reinforced CS presentations increased resistance to extinction in Experiment I and facilitated conditioning in Experiment II relative to a condition in which the same post-trial shock was delivered 8 s after non-reinforced trials. Experiment III demonstrated that prior exposure to pairings of the shock reinforcer and the post-trial shock also enhanced subsequent conditioning, and thus ruled out an explanation of the facilitation in terms of the surprising nature of the post-trial stimulation.     

The effect of amphetamine and L-dopa on tetrabenazine-induced suppression of intracranial self-stimulation in the rat

Abstract.— The administration of d-amphetamine sulphate resulted in a restoration of intracranial self-stimulation (ICSS) suppressed by tetrabenazine (TBZ). A dose-dependent increase in the rate of ICSS was seen after l-dopa in animals pretreated with TBZ. d-Amphetamine is believed to act by facilitating the nerve-impulse induced release of central catecholamines (CA) whereas the blockage of the granular uptake-storage mechanism by TBZ will prevent the storage of CA formed from the administrated l-dopa and thereby interfere with their release by nerve-impulses. Thus, in the latter case, an activation of central CA receptors in all probability will be due to a dose-dependent diffusion of CA from nerve terminals. It is suggested that the failure to completely antagonize the TBZ-induced suppression of behaviour by l-dopa is due to the fact that a direct activation, independent of the nerve-impulse flow, of central CA receptors easily results in an overstimulation and a reduced specificity in behaviour.     

The role of top-down suppression in mitigating the disruptive effects of task-irrelevant feature changes in visual working memory

Studies of change detection have shown that changing the task-irrelevant features of remembered objects impairs change detection for task-relevant features, a phenomenon known as the irrelevant change effect. Although this effect is pronounced at short study-test intervals, it is eliminated at longer delays. This has prompted the proposal that although all features of attended objects are initially stored together in visual working memory (VWM), top-down control can be used to suppress task-irrelevant features over time. The present study reports the results of three experiments aimed at testing the top-down suppression hypothesis. Experiments 1 and 2 tested whether the magnitude or time course of the irrelevant change effect was affected by the concurrent performance of a demanding executive load task (counting backwards by threes). Contrary to the top-down suppression view, the decreased availability of executive resources did not prolong the duration of the irrelevant change effect in either experiment, as would be expected if these resources were necessary to actively suppress task-irrelevant features. Experiment 3 showed that a visual pattern mask eliminates the irrelevant change effect and suggests that the source of the effect may lie in the use a high-resolution, sensory memory representation to match the memory and test displays when no task-irrelevant feature changes are present. These results suggest that the dissipation of the irrelevant change effect over time likely does not depend on the use of top-down control and raises questions about what can be inferred about the nature of storage in VWM from studies of this effect.     

The US preexposure phenomenon in the conditioned suppression paradigm: A role for conditioned situational stimuli

Four experiments evaluated possible associative and nonassociative accounts of the retardation in the acquisition of conditioned suppression produced by repeated prior exposure to an electric shock US. Associative interference resulting from conditioning of situational stimuli during preexposure to shock was suggested by the findings that signaling the occurrence of high-intensity shock with a discrete nontarget CS during the preexposure phase reduced the magnitude of the retardation effect compared to an unsignaled shock preexposure treatment (Experiments 1 and 4), nonreinforced presentations of putatively conditioned situational stimuli prior to conditioned suppression training reduced the magnitude of the retardation effect (Experiment 2), and the magnitude of the retardation effect was directly related to the intensity of preexposure shock (Experiment 3). Nonassociative interference was suggested by the finding that signaling the occurrence of low-intensity shock with a discrete nontarget CS during the preexposure phase did not reduce the magnitude of the retardation effect compared to an unsignaled shock preexposure treatment (Experiment 4). It was suggested that associative and nonassociative mechanisms govern the US preexposure phenomenon obtained in the conditioned suppression paradigm, and their relative contribution depends upon the intensity of shock.     

The role of the nucleus basalis magnocellularis in fear conditioning consolidation in the rat

The nucleus basalis magnocellularis (NBM) is known to be involved in the memorization of several conditioned responses. To investigate the role of the NBM in fear conditioning memorization, this neural site was subjected to fully reversible tetrodotoxin (TTX) inactivation during consolidation in adult male Wistar rats that had undergone fear training to acoustic conditioned stimulus (CS) and context. TTX was stereotaxically administered to different groups of rats at increasing intervals after the acquisition session. Memory was assessed as the conditioned freezing duration measured during retention testing, always performed 72 and 96 h after TTX administration. In this way, there was no interference with normal NBM function during either acquisition or retrieval phases, allowing any amnesic effect to be due only to consolidation disruption. The results show that for contextual fear response memory consolidation, NBM functional integrity is necessary up to 24 h post-acquisition. On the other hand, NBM functional integrity was shown to be necessary for memory consolidation of the acoustic CS fear response only immediately after acquisition and not 24-h post-acquisition. The present findings help to elucidate the role of the NBM in memory consolidation and better define the neural circuits involved in fear memories.     

Mesencephalic participation in the control of sexual behavior in the female rat

Electric stimuli applied to both pudendal nerves evoked field potentials, unit responses, and multiunit responses in the ventrolateral midbrain, in and around the peripeduncular nucleus. Bilateral lesions placed in this region suppressed sexual behavioral responses (lordosis and courting behavior) of ovariectomized rats primed with 5, 10, 100, and 1,000 microgram of estradiol benzoate and 2 mg of progesterone per kilogram of body weight. It is proposed that the region in question represents a relay station for the integration of sensory and endocrine information concerned in the control of receptive sexual behavior in the female rat.