Visualization of D1 dopamine receptors on living nucleus accumbens neurons and their colocalization with D2 receptors

To examine the substrate for dopamine (DA) synaptic action in the nucleus accumbens (nAcc), we visualized the cellular and subcellular distribution of DA receptors on postnatal nAcc neurons in culture using fluoroprobe derivatives of DA receptor ligands. Previously, we have shown that rhodamine-N-(p-aminophenethyl)-spiperone (NAPS) (10 nM), a derivative of the D2 antagonist spiperone, labels D2-like receptors on living nAcc neurons. We now show that rhodamine-Sch-23390 (30 nM), a derivative of the D1 antagonist, labels D1-like receptors. Putative specific membrane labeling reached a plateau after about 20 min. Labeling was stereospecific, as it was unaffected by competition with (-)-butaclamol, but blocked with (+)-butaclamol. We found that 52 +/- 7% of nAcc medium-sized neurons showed D1 labeling, which extended onto the dendrites. Labeling was also seen on presynaptic terminals, often abutting D1-positive and D1-negative cell bodies, consistent with a presynaptic modulatory role for D1 receptors. Larger neurons, which may be GABAergic or cholinergic interneurons, were also labeled. By sequential labeling first with rhodamine-Sch-23390 and then rhodamine-NAPS, we found that 38 +/- 6% of medium-sized neurons express both D1- and D2-like receptors, indicating that D1-D2 interactions may occur at the level of single postsynaptic neurons.     

Prospective study of the atopy preventive effect of maternal avoidance of milk and eggs during pregnancy and lactation

The preventive effect of maternal avoidance of cow's milk and eggs on the development of atopic dermatitis and sensitization to food allergens was studied in a prospective trial with families at high risk for atopy, intervention included encouraging exclusive breast feeding for at least 3 months and delaying the controlled introduction of solid foods. In addition, one group received a maternal diet with the complete avoidance of milk and eggs in the last trimester of pregnancy and during the period of exclusive breast feeding, another group had the same diet starting after delivery, and mothers of the third group had no dietary restrictions. The period prevalences of atopic dermatitis as well as the rates of specific sensitization to eggs and milk at 6 and 12 months were not significantly different between groups. We were unable to demonstrate a significant preventive effect of maternal diet. Conclusion: While breast feeding should be promoted for children at risk for atopy, mothers can be encouraged to stay on normal diet during pregnancy and the breast feeding period.     

Nicotinic receptor binding site probed with unnatural amino acid incorporation in intact cells

The nonsense codon suppression method for unnatural amino acid incorporation has been applied to intact cells and combined with electrophysiological analysis to probe structure-function relations in the nicotinic acetylcholine receptor. Functional receptors were expressed in Xenopus oocytes when tyrosine and phenylalanine derivatives were incorporated at positions 93, 190, and 198 in the binding site of the alpha subunit. Subtle changes in the structure of an individual side chain produced readily detectable changes in the function of this large channel protein. At each position, distinct features of side chain structure dominated the dose-response relation, probably by governing the agonist-receptor binding.     

Steady-state and transient delay analysis of ARQ protocols

A technique for the performance evaluation of ARQ protocols is presented. General distributions for the packet interarrival times at the transmitter are assumed. Two specific ARQ protocols, the stop-and-wait ARQ and the continuous ARQ are examined in particular. Both the transient and steady-state behaviour are obtained. A simple iterative scheme is proposed for the computation of the delay experienced by the packets and for the packet interdeparture time distribution. The latter result can be applied to the analysis of networks using an ARQ protocol in their datalink control layer. This method is demonstrated for the special case of a network consisting of N nodes connected in tandem. Analytical results are compared with simulation runs and excellent agreement is observed.     

Proinsulin levels in newborn siblings of type 1 (insulin-dependent) diabetic children and their mothers

Elevated proinsulin levels have been observed in healthy first degree relatives of Type 1 (insulin-dependent) diabetic patients. This elevation could reflect a sequele after a previous attack on the beta-cells not necessarily leading to diabetes, or represent a family trait related to the development of diabetes. When cord plasma levels of proinsulin, insulin and C-peptide from 14 newborn siblings of Type 1 diabetic patients were compared with 21 newborn control siblings unrelated to diabetic subjects, no differences were observed. Neither were any differences observed between their mothers at delivery when comparing the same parameters. In cord plasma the proinsulin levels (median and range) were higher than those in plasma from 35 adult fasting women unrelated to diabetic subjects (10, 5-83 pmol/l vs 4, 2-33 pmol/l; p < 0.001) whereas the C-peptide levels (median and range) were lower (0.20, 0.11-0.56 nmol/l vs 0.37, 0.21-0.69 nmol/l; p < 0.001). No differences in insulin levels using a highly specific insulin assay were observed. The results suggest that newborn children have high proinsulin and low C-peptide levels unrelated to heredity of diabetes and that the previously described elevated proinsulin level observed in older first degree relatives of diabetic subjects occurs later in life.     

Ventral intraparietal area of the macaque: anatomic location and visual response properties

1. The middle temporal area (MT) projects to the intraparietal sulcus in the macaque monkey. We describe here a discrete area in the depths of the intraparietal sulcus containing neurons with response properties similar to those reported for area MT. We call this area the physiologically defined ventral intraparietal area, or VIP. In the present study we recorded from single neurons in VIP of alert monkeys and studied their visual and oculomotor response properties. 2. Area VIP has a high degree of selectivity for the direction of a moving stimulus. In our sample 72/88 (80%) neurons responded at least twice as well to a stimulus moving in the preferred direction compared with a stimulus moving in the null direction. The average response to stimuli moving in the preferred direction was 9.5 times as strong as the response to stimuli moving in the opposite direction, as compared with 10.9 times as strong for neurons in area MT. 3. Many neurons were also selective for speed of stimulus motion. Quantitative data from 25 neurons indicated that the distribution of preferred speeds ranged from 10 to 320 degrees/s. The degree of speed tuning was on average twice as broad as that reported for area MT. 4. Some neurons (22/41) were selective for the distance at which a stimulus was presented, preferring a stimulus of equivalent visual angle and luminance presented near (within 20 cm) or very near (within 5 cm) the face. These neurons maintained their preference for near stimuli when tested monocularly, suggesting that visual cues other than disparity can support this response. These neurons typically could not be driven by small spots presented on the tangent screen (at 57 cm). 5. Some VIP neurons responded best to a stimulus moving toward the animal. The absolute direction of visual motion was not as important for these cells as the trajectory of the stimulus: the best stimulus was one moving toward a particular point on the face from any direction. 6. VIP neurons were not active in relation to saccadic eye movements. Some neurons (10/17) were active during smooth pursuit of a small target. 7. The predominance of direction and speed selectivity in area VIP suggests that it, like other visual areas in the dorsal stream, may be involved in the analysis of visual motion.