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.     

Multisensory spatial representations in eye-centered coordinates for reaching

Humans can reach for objects with their hands whether the objects are seen, heard or touched. Thus, the position of objects is recoded in a joint-centered frame of reference regardless of the sensory modality involved. Our study indicates that this frame of reference is not the only one shared across sensory modalities. The location of reaching targets is also encoded in eye-centered coordinates, whether the targets are visual, auditory, proprioceptive or imaginary. Furthermore, the remembered eye-centered location is updated after each eye and head movement. This is quite surprising since, in principle, a reaching motor command can be computed from any non-visual modality without ever recovering the eye-centered location of the stimulus. This finding may reflect the predominant role of vision in human spatial perception.     

Exposure to suicide: incidence and association with suicidal ideation and behavior: United States, 1994

Exposure to the suicide of another is common, but the magnitude and effects of such exposure are not well quantified. From a national random telephone survey of U.S. adults, we estimated the 12-month incidence of exposure to suicide and its association with suicidal ideation, planning, and behavior. Of 5,238 respondents, 342 (a weighted 7.0% representing 13.2 million persons) reported knowing a suicide decedent from the previous year. Univariate analysis showed persons reporting such exposure were significantly more likely to describe suicidal ideation and behavior than those unexposed; multivariate analysis showed no association. Though the risk related to suicide exposure may be small, given the magnitude of exposure, it may warrant intervention efforts because of its potential societal impact.     

The hippocampus and memory of verbal and pictorial material

Recognition of words and kaleidoscope pictures showed a double dissociation of left and right hippocampal activity using magnetic source imaging (MSI). MSI has advantages over alternative imaging techniques that measure hemodynamic changes for identifying regional changes in brain activity in real time and on an individual subject basis without the need for image subtraction. In this study, lists of words or kaleidoscope pictures were presented for memorization followed by tests of list items and foils during which brain activity was recorded. There was greater activation in the left than the right hippocampus with abstract nouns (e.g., relief) and greater activation in the right than the left hippocampus with kaleidoscope pictures. This dissociation was evident on a case by case basis. This study demonstrates the specialization of the two medial temporal lobe (MTL) regions, including the hippocampi, for mnemonic processing of verbal and pictorial items that are difficult to encode verbally.     

Radioligands for PET and SPECT Imaging of the central noradrenergic system

In the central nervous system, the neurotransmitter norepinephrine is involved in normal physiology, neuropsychiatric disorders, and the effects of numerous drugs. Although alterations of the central noradrenergic system are involved in the pathophysiology and pharmacotherapy of mood disorders, the basis and nature of these changes remain unresolved. Positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging agents will be valuable for further elucidating the roles of norepinephrine in health and disease. This review discusses PET and SPECT radioligands that have been developed for the enzymes, receptors, and transporters involved in noradrenergic neurotransmission. Currently, imaging agents that exhibit specific in vivo uptake in the brain have been described for monoamine oxidase A and beta-adrenergic receptors, but have not undergone detailed evaluation or experimental application. Based on the successful development and utilization of in vivo imaging agents for elements of the central dopaminergic and serotoninergic systems, PET and SPECT radioligands are expected to serve as new tools for studying the physiology, pathophysiology, and pharmacology of the central noradrenergic system.     

Cultural Diversity and Patients with Reduced Capacity: The Use of Ethics Consultation to Advocate for Mentally Handicapped Persons in Living Organ Donation

Theoretical Medicine and Bioethics - Living organ donation will soon become the source of the majority of organs donations for transplant. Should mentally handicapped people be allowed to donate,...     

A New View of Meditation

After years of meditating, are you still saddled with many of the same personal conflicts and interpersonal inhibitions that plagued you before you began? Rubin explores the hidden flaws in the meditative method itself. He explores Buddhism's ambivalent relationship to emotional life, and the negative consequences of letting go of experience. Detaching from experience may result in renouncing vital aspects of ourselves, such as constructive passion. The author argues that real meditation is transformative not tranquilizing, fostering a dynamic way of living.     

Are the interpersonal and identity disturbances in the borderline personality disorder criteria linked to the traits of affective instability and impulsivity?

This study examines the degree to which two putative biologically influenced personality traits, affective instability and impulsive aggression, are associated with some of the interpersonal and intrapsychic disturbances of borderline personality disorder (BPD) and with choice of defense mechanism. In a sample of 152 personality disorder patients, affective instability and impulsive aggression were measured. Defense mechanisms were assessed in 140 of these patients using the Defensive Style Questionnaire (DSQ). The correlations between the traits of affective instability and impulsive aggression and the eight DSM-III-R criteria for borderline personality disorder and 20 DSQ defenses were examined. Affective instability was significantly correlated with the DSM-III-R criteria of identity disturbance, chronic emptiness or boredom, inappropriate anger, suicidality, and the affective instability criteria. It also was associated with the defenses of splitting, projection, acting out, passive aggression, undoing, and autistic fantasy. Impulsive aggression was related to unstable interpersonal relationships, inappropriate anger and impulsiveness and with the defense of acting out. It was negatively correlated with the defenses of suppression and reaction formation. A number of the interpersonal and experiential disturbances and defense mechanisms that are features of BPD are associated with the traits of affective instability and impulsive aggression among patients with personality disorders.     

Asymptotic identifiability of nonparametric item response models

The identifiability of item response models with nonparametrically specified item characteristic curves is considered. Strict identifiability is achieved, with a fixed latent trait distribution, when only a single set of item characteristic curves can possibly generate the manifest distribution of the item responses. When item characteristic curves belong to a very general class, this property cannot be achieved. However, for assessments with many items, it is shown that all models for the manifest distribution have item characteristic curves that are very near one another and pointwise differences between them converge to zero at all values of the latent trait as the number of items increases. An upper bound for the rate at which this convergence takes place is given. The main result provides theoretical support to the practice of nonparametric item response modeling, by showing that models for long assessments have the property of asymptotic identifiability. The research was partially supported by the National Institute of Health grant R01 CA81068-01.