Thalamic inputs to the motor cortex studied in cats by retrograde axonal horseradish peroxidase transport

Thalamic afferent inputs of the motor cortex (area 4) were studied in cats by retrograde axonal transport of horseradish peroxidase (HRP). The main concentration of HRP-labeled neurons was found in rostral zones of the relay nuclei (of the ventrolateral and ventrobasal complex). A few labeled neurons were found in the mediodorsal association nucleus, where their distribution is quite local. HRP-labeled neurons of nonspecific intralaminar nuclei, projecting into the motor cortex, are present only in single numbers and show no tendency toward grouping in any parts of these nuclei. The results are evidence that the motor cortex receives heterogeneous afferentation from various thalamic nuclei, and it is evidently this which guarantees the reliability of transmission of incoming information.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 250–255, March–April, 1985.     

Backbone side-chain interactions in peptides

IR, ¹H-NMR and X-ray experiments have been carried out on dipeptides with the Pro-Asp and Pro-Asn sequences protected on both ends by amide groups. The Pro-Asp dipeptide was investigated for the carboxylic, methyl ester and carboxylate forms of the Asp residue.In solution, all dipeptides are found to accommodate almost exclusively the I-turn conformation stabilized by an interaction between the Asp or Asn-NH and CO bonds. The I-turn percentage roughly parallels the basicity of the Asp or Asn side substituent, and decreases from Asp^- to Asn, and to Asp or Asp (OMe).The I-turn, stabilized by the interaction involving the Asp-CO site, is retained in the crystal structure of the Pro-Asp(OMe) dipeptide. The Pro-Asp and Pro-Asn dipeptides assume a II-turn conformation in the solid state and the polar Asp or Asn side-groups are involved in a complex network of intermolecular interactions.     

Postsynaptic components of paroxysmal neuronal response in the strychninized neocortex

Neuronal response in the strychninized cortical suprasylvian gyrus was investigated in experiments on immobilized and unanesthetized cats using intracellular techniques. Paroxysmal depolarizing shifts (PDS) in neuronal membrane potential were recorded, consisting of a bursting discharge and slow depolarization wave. It was found when using intracortical stimulation that PDS can accumulate and change in shape and size. Bursting discharges in PDS were induced by large-scale EPSP which could be distinguished from paroxysmal response. Data from presumably intradendritic readings demonstrated the presence of large-scale EPSP during the generation of epileptiform discharges in the cortex. In a proportion of cells, PDS were accompanied by hyperpolarizing potentials — apparently IPSP, since they undergo reversal with intercellular administration of Cl^–. The contribution of excitatory and inhibitory synaptic influences to paroxysmal neuronal response is discussed.I. I. Mechnikov State University, Odessa. Translated from Neirofiologiya, Vol. 22, No. 5, pp. 642–649, September–October, 1990.     

Spruce budworm growth,development and food utilization on young and old balsam fir trees

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing, gravimetric analyses, a transfer experiment, and foliage chemical analyses at six dates during the period of budworm feeding activity indicated that the age of balsam fir, Abies balsamea, trees (70-year-old mature trees or 30-year-old juvenile trees) affected tree suitability for the spruce budworm via the chemical profile of the foliage. Insects reared on old trees had greater survival and pupal weight, shorter development times, and caused more defoliation than those reared on young trees. Young trees were more suitable for the development of young larvae (instars 2–5), while old trees were more suitable for the development of older, sixth-instar larvae. These results were confirmed by the laboratory transfer experiment. Young larvae fed foliage from young trees had higher relative growth rates (RGR), digestibility (AD), and efficiency of conversion of ingested foliage (ECI) than those fed foliage from old trees. These differences appeared to be related to the high N:tannins ratio, and the high contents of P present in young trees during the development of the young larvae. Old larvae fed foliage from old trees had higher relative growth rates, relative consumption rates (RCR), and digestibility of the foliage than those fed foliage from young trees. The high digestibility of the foliage of old trees was compensated for by a lower efficiency of conversion of digested food (ECD), which in turn resulted in no significant effect of tree age on the efficiency of conversion of ingested foliage by old larvae. The low relative consumption rate of old larvae fed foliage from young trees appeared to be related to the low N:tannins ratio, and the high contents of bornyl acetate, terpinolene, and °-3-carene present in young trees during the budworm sixth instar. Variations in these compounds in relation to tree age may serve as mechanisms of balsam fir resistance to spruce budworm by reducing the feeding rate of sixth instar larvae.     

The targeted force steps developed by a human wrist: Cyclic components in the motor program

The targeted flexor isometric force steps developed by a wrist and corresponding EMG activity of the flexor muscles were studied in healthy volunteers. In 82.3–97.5% of trials, the main component of the force trajectory (before the postcorrections of the force level) showed complex dynamics: several (from two to five)dF/dt peaks were observed at this section of the trajectory. The distribution of time intervals from the initiation of the force trajectory todF/dt peaks was polymodal in all cases. The mean interval between successivedF/dt peaks varied from 56.7 msec to 84.4 msec in different individuals (the average group value was 70.5 msec). All tested subjects exhibited amplitude modulation of integrated EMG at the section reflecting the force step development; the averaged interval between the successive first-order EMG peaks calculated for the group of five persons was 78.6 msec. Strict temporal correlation ofdF/dt peaks and EMG peaks was found (coefficient of correlation averaged 0.94). It is concluded that the motor command ensuring performance of isometric force step includes a cyclic component; this feature must be taken into account when mechanisms controlling such motor events are interpreted. The frequency of the component is near the upper limit of a normal tremor frequency band. At the same time, it is impossible to regard the cyclic component in the motor command as a result of simple superposition of tremor on the targeted force development because the cyclic component is clearly synchronized with the force step initiation.Neirofiziologiya/Neurophysiology, Vol. 25, No. 6, pp. 455–462, November–December, 1993.     

Crystal state conformation of three azapeptides containing the Azaproline residue,a β-turn regulator

The molecular structure of three protected AzaPro-containing peptides have been determined by x-ray diffraction: Z-AzaPro-NHiPr ( 1 ; Z: benzyloxycarbonyl), Z-AzaPro-L -Ala-NHiPr ( 2 ), and Boc-L -Ala-AzaPro-NHiPr ( 3 ; Boc: tert-butyloxycarbonyl). Starting from the key synthon benzyl-azaprolinate, compounds 1 , 2 , and 3 have been prepared by combined use of liquid phase peptide synthesis method and adequate isocyanates. In all peptides, the following geometric characteristics are retained: (a) pyramidal character of the two nitrogen atoms of the pyrazolidine ring; (b) pseudo cis conformation of the urethane ( 1 , 2 ) or tertiary amide ( 3 ) function preceding the AzaPro residue; (c) identical absolute values of the Azaproline residue torsion angles “?, ψ” respectively 111° and 23°. In compound 2 , the two nitrogen atoms of the pyrazolidine ring are R, R but the opposite S, S absolute configurations are observed in compound 3 . In the crystal, compound 3 adopts a folded structure similar to a type VI β-turn with a weak intramolecular i + 3 → i hydrogen bond, while an extended structure is observed in compound 2 . In the light of our findings, in a peptide chain and contrary to the Pro residue, an AzaPro residue should prevent the formation of any type of any type of β-turn with the residue following it but could accommodate a folded structure with a pseudo type VI βturn with the preceding residue. If confirmed, this would be of tremendous importance in the design of biologically active peptides and drugs. © 1993 John Wiley & Sons, Inc.     

Folded Structures in Protonated Reduced Dipeptides

Reduced dipeptides with the general formula RCO-Xaa- rXbb-N⁺HR′R′′ (rXbb, reduced analogue of residue Xbb: NH-C^α HR¹ -C_r H₂) are shown to adopt a folded conformation in solution and in the solid state. The protonated reduced amide bond is an active proton donor capable of interacting with a peptide carbonyl to give a strong hydrogen bond topologically equivalent to the i+2 or i+3? i interaction. The resulting conformation is similar to the γ- or β-turn structure found in peptides and proteins.