A novel subtype of prostacyclin receptor in the central nervous system.

Recently, in the course of our search for the prostacyclin receptor in the brain, we found a novel subtype, designated as IP2, which was finely discriminated by use of the specific ligand (15R)-16-m-tolyl-17,18,19,20-tetranorisocarbacyclin (15R-TIC) and specifically localized in the rostral part of the brain. In the present study, the tritiated compound 15R-[15-(3)H]TIC was synthesized and utilized for more specific research on IP2. The specificity of binding to rat brain regions was confirmed by use of several prostacyclin derivatives including 15S-TIC. Mapping of 15R- and 15S-[3H]TIC binding in adjacent pairs of frozen sections of rat brain demonstrated a quite similar pattern of distribution in almost all rostral brain regions, indicating that the regions may contain only the IP2 subtype. On the other hand, 15R-[3H]TIC binding was very faint as compared with 15S-[3H]TIC binding in the caudal medullary region. High densities of 15R-[3H]TIC binding sites were shown in the dorsal part of the lateral septal nucleus, thalamic nuclei, limbic structures, and some of the cortical regions. Scatchard plot analysis showed two components of high-affinity 15R-[3H]TIC binding in the rostral regions, one with a K(D) value at approximately 1 nM and the other with approximately 30 nM. These results strengthen our previous finding that a different subtype of prostacyclin receptor is expressed in the CNS, and the map with 15R-[3H]TIC obtained here could guide further studies on the molecular and functional properties of the IP2.

Electromyographic kinesiology of lower extremity muscles during slope walking.

To investigate the phasic activity of the lower extremity muscles during up- and downslope walking, five muscles of ten healthy men were examined by telemetered electromyography (EMG). The muscles were the tibialis anterior (TA), gastrocnemius (Gc), rectus femoris (RF), semitendinosus (St) and gluteus maximus (GM). The inclination of the slope was 3, 6, 9 and 12 degrees. EMG of the muscles and the time factors of a walking cycle were recorded by a 12-channel polygraph simultaneously. In upslope walking, the duration of TA, St and GM activity was longer and that of RF activity was shorter than in level walking. The phasic pattern of Gc in upslope walking was the same as in level walking. In downslope, the duration of Gc and RF activity was longer than on the level. St showed biphasic activities. The phasic pattern of TA and GM was nearly the same as in level walking. The phasic activity of the muscles altered with an inclination over 6 degrees in upslope, and over 3 degrees in downslope. The findings indicate that the muscles stabilize the knee and ankle joint much more in slope walking than in level walking, and in slope walking they also exert themselves to elevate or lower the body weight.