Challenging issues in rheumatology: thoughts and perspectives

Clinical Rheumatology -     

A perception-based ERP reveals that the magnitude of delay matters for memory-guided reaching

Delayed action research has suggested that perceptual information about a visual stimulus decays over several seconds. With event-related potential (ERP) methodology, one should be able to track the time course of the electrophysiological processes associated with this decay. Recently, Cruikshank et al. (J Vis 12:29, 2012) found that the N170 ERP component reflected ventral stream processes linked to motor planning and perception for action. Specifically, the N170 was larger for actions that relied on perceptual-based information. However, the delay interval was very short (tens of ms). Behavioral and neuroimaging studies suggest that when longer delays are employed, reactivation of ventral areas is necessary in order to access a stored representation of the target’s characteristics. Therefore, the N170 may reflect not only the perception-for-action processes, but also the accuracy of the representation. In order to test this, we traced the time course of the N170 in memory-guided reaching when 1-, 2-, and 3-s delays separated target occlusion and response initiation. During reach initiation, the N170 was more negative and peaked earlier for the 1 s than the 2- and 3-s delays and correlated significantly with performance at the longest delay. These results suggest that the neural mechanisms involved in movement planning change for delays beyond 1 s. The smaller N170 may reflect an impoverished visual perceptual representation in the ventral stream. To our knowledge, these are the first electrophysiological results to suggest that there is decay of visual perceptual information that occurs with increasing time.     

Brief and extended abstinence from chronic oral methylphenidate treatment produces reversible behavioral and physiological effects

Methylphenidate (MP) is a commonly prescribed psychostimulant to individuals with Attention Deficit Hyperactivity Disorder, and is often used illicitly among healthy individuals with intermittent breaks to coincide with breaks from school. This study examined how intermittent abstinence periods impact the physiological and behavioral effects of chronic oral MP self-administration in rats, and whether these effects persist following prolonged abstinence from the drug. Rats were treated orally with water, low-dose (LD), or high-dose (HD) MP, beginning at PND 28. This daily access continued for three consecutive weeks followed by a 1-week abstinence; after three repeats of this cycle, there was a 5-week abstinence period. Throughout the study, we examined body weight, food intake, locomotor activity, and anxiety- and depressive-like behaviors. During the treatment phase, HD MP decreased body weight, food intake, and depressive- and anxiety-like behaviors, while it increased locomotor activity. During intermittent abstinence, the effects of MP on locomotor activity were eliminated. During prolonged abstinence, most of the effects of HD MP were ameliorated to control levels, with the exception of weight loss and anxiolytic effects. These findings suggest that intermittent exposure to chronic MP causes physiological and behavioral effects that are mostly reversible following prolonged abstinence.     

Effects of Insulin-like Growth Factor-I and its Analogue,Long-R 3 -IGF-I,on Intestinal Absorption of 3- O -methyl- d -glucose are Less Pronounced than Gut Mucosal Growth Responses

The relationship between insulin-like growth factor-I (IGF-I) peptide-induced increases in bowel mass and functional improvement is unclear. We utilised three independent methods to investigate the effects of IGF-I peptides on intestinal absorption of the glucose analogue, 3- O -methyl- d -glucose (3MG) in rats. Rats received vehicle, IGF-I or the more potent analogue, long-R 3 -IGF-I via subcutaneously implanted mini-pump, for 7 days, at which time intestinal absorption was assessed by: (1) plasma 3MG appearance following oral gavage, (2) single-pass- or (3) recirculating-perfusion of a jejunal segment. 3MG (320 or 800 &#117 mg) was gavaged on day 7 to rats treated with vehicle, IGR-I or long-R 3 -IGF-I. With the lower 3MG dose, only long-R 3 -IGF-I increased (40%) the initial rate of 3MG appearance in plasma. IGF-I had no significant effect, whilst at the higher 3MG dose neither peptide was effective. Utilising perfusion techniques, long-R 3 -IGF-I, but not IGF-I, significantly increased 3MG uptake per cm of jejunum by up to 69%, although significance was lost when expressed as a function of tissue weight. Long-R 3 -IGF-I, but not native IGF-I, enhanced 3MG absorption from the intestinal lumen, presumably reflecting an increased mucosal mass rather than an up-regulation of specific epithelial glucose transporters.     

Hyperventilation-induced high-amplitude rhythmic slowing with altered awareness: a video-EEG comparison with absence seizures

PURPOSE: Hyperventilation-induced high-amplitude rhythmic slowing (HIHARS) in children may be associated with clinical episodes of altered awareness. The presence of automatisms has been proposed as a distinguishing feature that helps to differentiate absence seizures from nonepileptic causes of decreased responsiveness. This retrospective, controlled, video-EEG study compared the clinical characteristics of episodes of HIHARS with loss of awareness with those of absence seizures. METHODS: The database of a tertiary Children's Hospital was searched for patients studied between April 1993 and April 1997 who had at least one episode of HIHARS with loss of awareness. The absence control group was obtained by selecting the next patient, after an HIHARS study subject, who met the following criteria: (a) had at least one absence seizure occurred during hyperventilation in the EEG recording, and (b) had a diagnosis of idiopathic generalized epilepsy. The video-EEG and medical histories of all patients were reviewed and summarized. RESULTS: We reviewed video-EEG recordings of 77 episodes of HIHARS with loss of awareness from 22 children and 107 absence seizures during hyperventilation from 22 children. Eye opening and eyelid flutter were seen more frequently in absence seizures, whereas fidgeting, smiling, and yawning occurred more frequently during HIHARS episodes. Arrest of activity, staring, and oral and manual automatisms were observed in both groups. CONCLUSIONS: Automatisms are common in both HIHARS and absence seizures. Yawning, smiling, and particularly fidgeting occur more commonly and eye opening and eyelid flutter less commonly in HIHARS. However, episodes of HIHARS with loss of awareness clinically mimic absence seizures, and these conditions can be distinguished reliably only by EEG.     

Obesity,appearance, and psychosocial adaptation in young African American children

OBJECTIVE: To evaluate the contributions of weight status, skin tone, peer teasing, and parental appraisals of child's size to self-esteem and psychosocial adjustment in overweight African American children. METHOD: Overweight to very obese 5- to 10-year-old African American children (N = 117) completed measures of self-esteem, skin tone satisfaction, peer teasing, and body size perception. Caregivers completed the Child Behavior Checklist and rated their child's body size. RESULTS: Overweight was associated with low appearance self-esteem, and body size dissatisfaction with low global self-worth and low appearance self-esteem in children 8 and older. Appearance self-esteem but not global self-worth was lower in girls than boys. Parental perception of child's size as heavier than average was associated with low child appearance self-esteem. Heavier children also had more parental report of behavior and psychosocial problems, but their scores were in the nonclinical range. Child skin tone dissatisfaction was associated with low global self-worth. Weight-related peer teasing was associated with low self-esteem. CONCLUSIONS: The relationship between obesity and self-esteem in African American children depends upon age, gender, and children's experiences with teasing and parental evaluation of their size. Other factors, like skin tone satisfaction, contribute to a child's sense of self-worth.