The effect of stimulation of the deep layers of somatosensory zones CI and CII on the activity of motor zone MI of the cat cortex]

The influence of electrical stimulation of deep layers of the somatosensory zones CI and CII on unit responses and intercortical evoked potentials (IEP) in the motor cortical zone MI in projection areas of the anterior contralateral limb was studied in cats anaesthetized with Nembutal and immobilized with diplacine. Latencies of the main IEP components and their different behaviour during repeated stimulation, experimental hypoxia and Nembutal administration suggested the presence of intercortical connections of an oligo- and polysynaptic nature. Only 22% of the MI zone units proved to be responsive to CI and CII stimulation; the latencies of the unit discharges varied from 4.3 to 35 msec. A relatively smaller effectiveness of short-latency inputs from CI and CII to MI was recorded as compared with long latency ones.     

Concanavalin A distorts the beta-GlcNAc-(1-->2)-Man linkage of beta- GlcNAc-(1-->2)-alpha-Man-(1-->3)-[beta-GlcNAc-(1-->2)-alpha-Man- (1-- >6)]-Man upon binding

Carbohydrate recognition by proteins is a key event in many biological processes. Concanavalin A is known to specifically recognize the pentasaccharide core (beta-GlcNAc-(1-->2)-alpha- Man-(1-->3)-[beta- GlcNAc-(1-->2)-alpha-Man-(1-->6)]-Man) of N-linked oligosaccharides with a Ka of 1.41 x 10(6 )M-1. We have determined the structure of concanavalin A bound to beta-GlcNAc-(1-->2)-alpha-Man-(1-->3)-[beta- GlcNAc-(1-->2)-alpha-Man- (1-->6)]-Man to 2.7A. In six of eight subunits there is clear density for all five sugar residues and a well ordered binding site. The pentasaccharide adopts the same conformation in all eight subunits. The binding site is a continuous extended cleft on the surface of the protein. Van der Waals interactions and hydrogen bonds anchor the carbohydrate to the protein. Both GlcNAc residues contact the protein. The GlcNAc on the 1-->6 arm of the pentasaccharide makes particularly extensive contacts and including two hydrogen bonds. The binding site of the 1-->3 arm GlcNAc is much less extensive. Oligosaccharide recognition by Con A occurs through specific protein carbohydrate interactions and does not require recruitment of adventitious water molecules. The beta-GlcNAc-(1-->2)-Man glycosidic linkage PSI torsion angle on the 1-->6 arm is rotated by over 50 degrees from that observed in solution. This rotation is coupled to disruption of interactions at the monosaccharide site. We suggest destabilization of the monosaccharide site and the conformational strain reduces the free energy liberated by additional interactions at the 1-->6 arm GlcNAc site.      

Characteristics of inhibition in the kitten sensory-motor cortex

Responses of 340 neurons of the sensory-motor cortex to electric shocks applied to the limbs were investigated in kittens aged 3–30 days. In 9.4% of cells of kittens aged 3–10 days and in 17.1% of cells in kittens aged 21–30 days pauses were observed immediately after the excitatory component of the extracellular response. Intra- and quasiintracellular recording showed that postsynaptic inhibition participates in the genesis of these pauses. The IPSPs which, as a rule, followed the excitatory component of the response were of much longer duration (up to 250–380 msec) than the analogous IPSPs in the sensory-motor cortex of adult cats. Usually the amplitude of the IPSP in kittens did not exceed 5 mV.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 227–231, May–June, 1977.     

High rate of recent transposable element-induced adaptation in Drosophila melanogaster

Although transposable elements (TEs) are known to be potent sources of mutation, their contribution to the generation of recent adaptive changes has never been systematically assessed. In this work, we conduct a genome-wide screen for adaptive TE insertions in Drosophila melanogaster that have taken place during or after the spread of this species out of Africa. We determine population frequencies of 902 of the 1,572 TEs in Release 3 of the D. melanogaster genome and identify a set of 13 putatively adaptive TEs. These 13 TEs increased in population frequency sharply after the spread out of Africa. We argue that many of these TEs are in fact adaptive by demonstrating that the regions flanking five of these TEs display signatures of partial selective sweeps. Furthermore, we show that eight out of the 13 putatively adaptive elements show population frequency heterogeneity consistent with these elements playing a role in adaptation to temperate climates. We conclude that TEs have contributed considerably to recent adaptive evolution (one TE-induced adaptation every 200-1,250 y). The majority of these adaptive insertions are likely to be involved in regulatory changes. Our results also suggest that TE-induced adaptations arise more often from standing variants than from new mutations. Such a high rate of TE-induced adaptation is inconsistent with the number of fixed TEs in the D. melanogaster genome, and we discuss possible explanations for this discrepancy.     

Facial motor responses to microstimulation of the superior colliculi in the white mouse

Facial motor responses to microstimulation of different zones of the superior colliculi have been investigated in the albino mice craniotomized under thiopental anaesthesia. Local responses of the mystacial vibrissae, upper lip and eyelids were initiated by microstimulation of the rostral parts of the inner layers of the colliculus superior (high-frequency volleys of 5-7 pulses with a current limit of 35 microA). Sequential changes in the pattern of facial responses were observed within microelectrode traces indicating vertical orientation of facial motor representations in the superior colliculus. Some differences in the localization and pattern of facial responses in the right and left superior colliculi were revealed: 1) vibrissae and lip representations in the right superior colliculus occupy more extensive zone (vertical distribution from 300 to 2,300 microns) as compared to those in the left one (700-2,000 microns); 2) microstimulations of the right superior colliculus produce both uni- and bilateral vibrissal motor responses, whereas stimulation of the left superior colliculus evokes only unilateral responses. The duration of the latent period of the vibrissal and lip motor responses to stimulation of the right superior colliculus varied from 10 to 26 ms (16.1 +/- 2.4 ms; n = 199), to stimulation of the left one-from 10 to 18 ms (mean 14.9 +/- 1.8 ms; n = 55). It is suggested that polysynaptic motor responses to microstimulation of the superior colliculi are realized via the reticular and other premotor nuclei of the brain stem which have direct inputs from the superior colliculus and direct projections to the facial motor nucleus.     

Population genomics of transposable elements in Drosophila melanogaster

Transposable elements (TEs) are the primary contributors to the genome bulk in many organisms and are major players in genome evolution. A clear and thorough understanding of the population dynamics of TEs is therefore essential for full comprehension of the eukaryotic genome evolution and function. Although TEs in Drosophila melanogaster have received much attention, population dynamics of most TE families in this species remains entirely unexplored. It is not clear whether the same population processes can account for the population behaviors of all TEs in Drosophila or whether, as has been suggested previously, different orders behave according to very different rules. In this work, we analyzed population frequencies for a large number of individual TEs (755 TEs) in five North American and one sub-Saharan African D. melanogaster populations (75 strains in total). These TEs have been annotated in the reference D. melanogaster euchromatic genome and have been sampled from all three major orders (non-LTR, LTR, and TIR) and from all families with more than 20 TE copies (55 families in total). We find strong evidence that TEs in Drosophila across all orders and families are subject to purifying selection at the level of ectopic recombination. We showed that strength of this selection varies predictably with recombination rate, length of individual TEs, and copy number and length of other TEs in the same family. Importantly, these rules do not appear to vary across orders. Finally, we built a statistical model that considered only individual TE-level (such as the TE length) and family-level properties (such as the copy number) and were able to explain more than 40% of the variation in TE frequencies in D. melanogaster.     

Design and applicability of DNA arrays and DNA barcodes in biodiversity monitoring

Background  

The rapid and accurate identification of species is a critical component of large-scale biodiversity monitoring programs. DNA arrays (micro and macro) and DNA barcodes are two molecular approaches that have recently garnered much attention. Here, we compare these two platforms for identification of an important group, the mammals.     

Muscle afferent modulation by stimulation of motor and supplementary motor cortex in cats

Local stimulation in the zone of motor representation of the cat hind limb in the postcruciate cortex (area 4) modulates afferent activity of flexor spindles of the foot. An initial pause, connected with contraction of extrafusal fibers, is observed in this activity. After the muscle has returned to its original length, a sharp rise of discharge frequency develops followed by a return to its initial level. Similar phases, but less marked, are observed in secondary afferents. Stimulation of contralateral and ipsilateral regions of the medial precruciate cortex (area 6) causes selective, intensive, and prolonged facilitation of discharge of type Ia units followed by an after-effect, without involving extrafusal muscle fibers. Since influences of the premotor supplementary cortex on lumbar gamma motoneurons are relatively independent of influences coupled with activation of the alpha system on muscle afferents from the motor cortex, a specific role of area 6 in the regulation of segmental excitability of the gamma system can be postulated.