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Notes: Summary Intracellular recording was made in the C3-C4 segments from cell bodies of a previously described system of propriospinal neurones (PNs), which receive convergent monosynaptic excitation from different higher motor centres and mediate disynaptic excitation and inhibition from them to forelimb motoneurones. Inhibitory effects in these PNs have now been investigated with electrical stimulation of higher motor centres and forelimb nerves. Short-latency IPSPs were evoked by volleys in the cortico-, rubro- and tectospinal tracts and from the reticular formation. Latency measurements showed that those IPSPs which required temporal summation were disynaptically mediated. After transection of the corticospinal tract in C2, only small and infrequent disynaptic IPSPs were evoked from the pyramid. It is postulated that disynaptic pyramidal IPSPs only to a small extent are evoked by monosynaptic excitation of reticulospinal inhibitory neurones known to project directly to the PNs, and that they are mainly mediated by inhibitory interneurones in the C3-C4 segments. Tests with spatial facilitation revealed monosynaptic excitatory convergence from tecto-, rubro- and probably also from reticulospinal fibres on inhibitory interneurones monosynaptically excited from corticospinal fibres (interneuronal system I). Disynaptic IPSPs were also evoked in the great majority of the PNs by volleys in forelimb muscle and skin nerves. A short train of volleys was usually required to evoke these IPSPs from group I muscle afferents. In the case of cutaneous nerves and mixed nerves single volleys were often effective, and the lack of temporal facilitation of IPSPs produced by a train of volleys showed strong linkage from these nerves. The results obtained after transection of the dorsal column at different levels show that the relay is almost entirely rostral to the forelimb segments. Test with spatial facilitation revealed that interneurones monosynaptically activated from forelimb afferents receive convergent excitation from corticospinal but not or only weakly so from tecto- or rubrospinal fibres. There was also convergence from group I muscle afferents and low threshold cutaneous afferents on common interneurones. It is postulated that the disynaptic IPSPs from forelimb afferents are mediated by inhibitory interneurones (interneuronal system II) other than those receiving convergent descending excitation. Volleys in corticospinal fibres, in addition to the disynaptic IPSPs, evoke late IPSPs in the PNs. Similar late IPSPs were evoked from the ipsilateral forelimb by stimulation of the FRA. Monosynaptic IPSPs were evoked in the majority of the PNs on weak stimulation of the lateral reticular nucleus (LRN) and from regions dorsal to it. Results from threshold mapping suggest that these IPSPs are due to antidromic stimulation of ascending inhibitory neurones which also project to the C3-C4 PNs, and that the ascending collaterals terminate in the LRN or/and the base of the cuneate nuclei. Activity in the ascending collaterals may give higher centres information regarding inhibitory control of the PNs. It is postulated that interneuronal system I subserves descending feed-forward inhibition and interneuronal system II feed-back inhibition from the forelimb of transmission through the C3-C4 PNs to motoneurones.

Notes: Small-angle x-ray diffraction measurements were performed upon dimethyl acetamide (DMAc) solutions of four samples of X-500, an aromatic polyamide-hydrazide. The solubility improved as the polymer molecular weight increased, the most soluble sample being in the form of a highly oriented, crystalline fiber. Molecular weights determined from the scattering curves indicate that aggregation was present in all solutions. Its extent varied with the solubility of the sample, increased with polymer concentration and, for the lowest concentrations studied, could be reduced by the addition of acetic acid. Radius of gyration values were smaller than those obtained by light scattering, probably because of insufficient resolution of the camera. The mass per unit length along the chain was found to be 18-20 Å, while the radius of gyration of the cross section was 3.5-4.8 Å. Three of the samples gave nearly the same angular intersection for the coil-and rodlike regions of the scattering curve. Two of these were whole polymers and the other a narrow fraction. The fact that essentially the same intercept was found in all three cases indicates the persistence length as measured for linear chain polymers by small-angle x-ray diffraction is independent of the heterogeneity of the sample. The intercepts, after a small correction for excluded volume effects, correspond to persistence lengths in the range 71-88 Å for DMAc solutions, which approximate those determined for dimethyl sulfoxide (DMSO) solutions by light scattering the intrinsic viscosity without correction for excluded volume, but are substantially larger than the DMSO values, corrected for excluded volume of 30-49 Å. We can offer no explanation for this difference.

Notes: Perfluorobutenyloxyphthalic anhydride (PFPA) has been synthesized as a new curing agent for epoxy resins, and the properties of epoxy resin cured with PFPA have been investigated. Good PFPA synthesis yields were realized by a dehydrating ring closure of perfluorobutenyloxyphthalic acid, which was obtained through the reaction of hexafluoropropene trimers with 4-hydroxyphthalic acid. Epoxy resin cured with PFPA was found to have several excellent properties. Its boilding water absorption was 0.45%, which is about a one-fourth that for conventionally cured epoxy resin. Its heat resistance was excellent, and its critical surface tension was almost the same as for PTFE.