The relationship between the Stiles–Crawford effect of the first kind (SCE-I) and myopia

The Stiles-Crawford effect of the first kind (SCE-I) was measured on both emmetropic and myopic subjects at six different retinal locations. The results revealed a number of significant discrepancies in receptor alignment between the groups of different refractive errors. In myopic subjects, the receptors in the nasal retina (i.e. between the fovea and the optic nerve head) were found to be aligned nasally towards the optic nerve head, whereas the receptors in the temporal retina were aligned towards the centre of the exit pupil. In emmetropic subjects, the receptors across the retina were finely tuned towards the centre of the exit pupil. The magnitude of the receptor displacement in myopic subjects was found to be directly associated with the length of the eyeball.     

Major histocompatibility complex class II (HLA-DRB and -DQB) allele frequencies in Botswana: association with human immunodeficiency virus type 1 infection

Southern Africa is facing an unprecedented public health crisis due to the high prevalence of human immunodeficiency virus type 1 (HIV-1). Vaccine development and testing efforts, mainly based on elicitation of HIV-specific T cells, are under way. To understand the role of human leukocyte antigen (HLA) class II alleles in HIV pathogenesis and to facilitate HLA-based HIV-1 vaccine design, we analyzed the frequencies of HLA class II alleles within the southern African country of Botswana. Common HLA class II alleles were identified within the Botswana population through the molecular genotyping of DRB and DQB1 loci. The DRB1 allele groups DRB1*01, DRB1*02/15, DRB1*03, DRB1*11, and DRB1*13 were encountered at frequencies above 20%. Within the DQB1 locus, DQB1*06 (47.7%) was the most common allele group, followed by DQB1*03 (39.2%) and DQB1*04 (25.8%). We found that DRB1*01 was more common in HIV-negative than in HIV-positive individuals and that those who expressed DRB1*08 had lower median viral loads. We demonstrate that the frequencies of certain HLA class II alleles in this Botswana population differ substantially from those in North American populations, including African-Americans. Common allele groups within Botswana cover large percentages of other African populations and could be targeted in regional vaccine designs.     

Oxygen-dependent mechanisms in cerebral autoregulation

Autoregulatory adjustments in the caliber of cerebral arterioles were studied in anesthetized cats equipped with cranial windows for the direct observation of the pial microcirculation. Increased venous pressure caused slight, but consistent, arteriolar dilation, at normal and at reduced arterial blood pressure and irrespective of whether or not intracranial pressure was kept constant or allowed to increase. Arterial hypotension caused arteriolar dilation which was inhibited partially by perfusion of the space under the cranial window with artificial CSF equilibrated with high concentrations of oxygen. This vasodilation was inhibited to a greater extent by perfusion of the space under the cranial window with fluorocarbon FC-80, equilibrated with high concentrations of oxygen. CSF or fluorocarbon equilibrated with nitrogen did not influence the vasodilation in response to arterial hypotension. The response to increased venous pressure was converted to vasoconstriction when fluorocarbon equilibrated with high concentrations of oxygen was flowing under the cranial window. The vasodilation in response to arterial hypotension was inhibited by topical application of adenosine deaminase. The results show that both metabolic and myogenic mechanisms play a role in cerebral arteriolar autoregulation. Under normal conditions, the metabolic mechanisms predominate. The presence of the myogenic mechanisms may be unmasked by preventing the operation of the metabolic mechanisms. The major metabolic mechanism seems to be dependent on changes in PO₂ within the brain with secondary release of adenosine.     

Association between seasonal affective disorder and the 5-HT2A promoter polymorphism, -1438G/A

Genes involved in serotonin metabolism are good candidates for the pathogenesis of seasonal affective disorder (SAD). A functional variant in the serotonin transporter promoter, 5-HTTLPR, has recently been shown to be associated with SAD and seasonality. The purpose of this study was to determine whether -1438G/A, a polymorphism in the 5-HT2A promoter, is associated with SAD and seasonality, and whether it has additive effects with 5-HTTLPR on seasonality. Sixty-seven individuals with SAD and 69 normal volunteers, all screened with the SCID and diagnosed according to DSM-III-R criteria, were genotyped for the -1 438G/A 5-HT2A promoter polymorphism. All had been previously genotyped for 5-HTTLPR and had been assessed for seasonality by the Global Seasonality Scale. There was a significant increase in the frequency of the -1438A variant allele of the 5-HT2A promoter polymorphism in SAD patients (0.47) compared to matched controls (0.36) (P < 0.01). The difference in genotype distribution was also significant (P < 0.05). We found no association between the -1438G/A polymorphism and seasonality scores, and there was no additive effect with 5-HTTLPR on seasonality. In conclusion, we have shown that the -1438G/A 5-HT2A promoter variant is associated with SAD but not with seasonality. We suggest that the association may instead be with the depressive symptoms of SAD. However, these results should be treated with caution until replicated because of the possibility of false-positive findings in case-control association studies.     

Anomalous kinetic visual fields found in family members of patients with a confirmed diagnosis of Gilles de la Tourette syndrome.

Three visual manifestations of Gilles de la Tourette syndrome (TS), a neuropsychiatric disorder, have been previously reported. In this paper we report anomalies in the measured kinetic paracentral visual field of TS patients and their family members. We found that 96% of TS patients exhibited paracentral kinetic visual field defects (nasal and temporal steps, enlargement, "ringing," and/or baring of the blind spot). Ninety-three percent of fathers of TS children and, surprisingly, about 80% of mothers exhibit these characteristic visual field anomalies. Sample data and examples of family studies are reported.     

Scopolamine Effects on Visual Information Processing, Attention, and Event-Related Potential Map Latencies

We measured performance and event-related brain potential (ERP) map latencies in 12 subjects during four visual discrimination tasks to compare the timing of scopolamine effects on information processing and attention. "Topographic component recognition" found ERP map latencies at times of best fit with a component model map. This "common topography" criterion minimized topographic differences among conditions to facilitate latency interpretations. Scopolamine slowed N1 latency in all tasks, and P3 and reaction time in some tasks. The drug delayed responses to easy targets more than to hard targets. It also induced a disproportionate N1 delay for unilateral high spatial frequency gratings. Both effects reflect a scopolamine-induced impairment when processing targets that usually capture attention. Scopolamine also impaired accuracy for unilateral high spatial frequency gratings, and for gratings presented at probable locations, confirming and extending previous findings. Scopolamine-induced P1 and N1 delays showed that visual processing was affected. Several results were inconsistent with a serial stage model. We suggest that scopolamine both delays selected processes and impairs a processing mode based on automatic capture of attention, inducing more serial processing.