A model for the functioning of the striatum

A model is presented for the operation of the striatum. The model posits that the basal ganglia are responsible for driving smooth transitions of state for an organism. We propose that this is accomplished through the computation of a potential function within the striatum on which a gradient descent is performed toward the goal state. The model suggests that various somatotopic regions of the striatum correspond to state spaces, each of which pertains to a different aspect of the organism. This paper discusses this model only in the context of motor control, i.e., egomotion and limb movement. The model appears to account for a variety of experimental results, and for some unusual properties of the striatum.     

Testosterone 5 alpha-reductase activity in neural tissue of fetal rhesus macaques

After development of a 5 alpha-reductase activity (5 alpha-RA) assay based on the capacity of microsomes to convert [3H]testosterone (T) to [3H]dihydrotestosterone (DHT), we analyzed 5 alpha-RA in neural tissues of fetal rhesus macaques at 50, 80 and 150 days of gestation. This method allowed us to collect kinetic data on the properties of the 5 alpha-reductase resident in fetal brain at 150 days of gestation. The Km and Vmax calculated from these data were 4.32 microM and 22.6 nmol.mg protein-1.h-1, respectively. Analyses of 5 alpha-RA in microsomes from the hypothalamic-preoptic area-amygdala (HPA) at dilutions of 1/25 and 1/50 indicated higher enzyme activity with increasing dilution of the microsomes. Measurement of 5 alpha-RA using concentrations of [3H]T which saturated the enzyme in diencephalon (DIEN), brain stem (B.STEM), temporal (TCTX) and frontal cortex (FCTX) of six 50-day old fetuses (3 males and 3 females) revealed no obvious sex differences in 5 alpha-RA, however, a significant difference (P less than 0.05) between tissues was noted. The DIEN and B.STEM contained significantly (P less than 0.05) higher levels 5 alpha-RA than the FCTX while the TCTX contained an intermediate level of activity. Significant increases in 5 alpha-RA were observed in FCTX and TCTX with time of gestation (50, 80 and 150 days). Other tissues, including amygdala, hippocampus, cerebellum, tegmentum and septum also change with fetal age. These data demonstrate the existence of 5 alpha-reductase in the fetal monkey brain. Significant changes in cortical 5 alpha-RA suggest some role for 5 alpha-reductase in development.     

In vivo assessment of tumor-induced nonspecific suppression of contact sensitivity

Summary Normal BALB/c mice were assessed for 2,4-dinitrofluorobenzene (DNFB)-induced contact sensitivity following adoptive transfer of macrophages (Mo). T cells, or their derived products, from normal or tumor-bearing hosts (TBH). Contact sensitivity (CS) was measured by a quantitative radioisotopic ear assay, a total in vivo system based on localization of IP-injected iodinated human serum albumin ([¹²⁵I]HSA) in the DNFB-challenged ear. Adoptive transfer of low or high doses of TBH T cells or their derived supernatants into normal recipients suppresed their responsiveness, while Mo supernatants enhanced it. Moreover, in all cases adoptive transfer of TBH cells or supernatants resulted in a lower CS response than did their normal counterparts. These results further corroborate our previous in vitro data indicating that T cells, or Mo and T cell soluble products, possess immunoregulatory capabilities in vivo.Abbreviations DNFB 2,4-dinitrofluorobenzene - TBH tumor-bearing host - Mo macrophages - ¹²⁵I-HSA iodinated-human serum albumin - CMI cell-mediated immunity - CS contact sensitivity; Ig, immunoglobulin - C complement     

Temperature-dependent changes in the swimming behaviour of Tetrahymena pyriformis-NT1 and their interrelationships with electrophysiology and the state of membrane lipids

The swimming velocity and the amplitude of the helical swimming path of T. pyriformis-NT1 cells grown at 20 degrees C (Tg 20 degrees C) and 38 degrees C (Tg 38 degrees C) were monitored between 0 and 40 degrees C in the presence and absence of electric fields. Within physiological limits the swimming velocity increased and the amplitude decreased as temperature was raised. The temperature profiles of these properties were not linear, and showed discontinuities at different temperatures for the different cultures. The break points in Arrhenius plots of the resting potential, regenerative spike magnitude, repolarization time, swimming velocity and swimming amplitude are tabulated and compared. The initial breakpoints upon cooling were clustered about the breakpoints in fluorescence polarization of D.P.H. in extracted phospholipids, and around the transition temperatures estimated from the literature for the pellicular membrane of these cells. The average of the initial breakpoints on cooling was 22.9 degrees C for Tg 38 degrees C cells and 13.7 degrees C for Tg 20 degrees C cells, a shift of 9.2 degrees C. Unlike Paramecium there is no depolarizing receptor potential in Tetrahymena upon warming. It is suggested that this may be the basis of a behavioural difference between Tetrahymena and Paramecium--namely that in Tetrahymena maximum swimming velocity occurs above growth temperature whereas in Paramecium the two points coincide. Swimming velocity and resting potential were correlated with membrane fluidity within physiological limits, but for other parameters the relationship with fluidity was more complex.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of temperature upon the electrophysiological properties of Tetrahymena pyriformis-NT1

Cells of Tetrahymena pyriformis--NT1 were cultured at 38 degrees C (Tg 38 degrees C) and 20 degrees C (Tg 20 degrees C) and their properties investigated over the range 0-40 degrees C. Tg 20 degrees C cells were viable in the range 3-33 degrees C and changes in their properties were readily reversible between 10 degrees C and 30 degrees C. Tg 38 degrees cells were viable in the range 40-10 degrees C and their property changes were immediately reversible in the range 40-23 degrees C. The I-V relations of Tg 38 degrees C cells showed increased excitability as the cells were cooled from 40 degrees C. At 10 degrees C there was a considerable loss of excitability and slope resistance. Cooling Tg 20 degrees C cells from 20 degrees C gave a similar pattern, although over a narrower temperature range. Warming Tg 20 degrees C Tetrahymena above 20 degrees C led to a progressive loss of excitability and the cells were markedly less viable above 35 degrees C. Within physiological limits the regenerative spike magnitude, repolarization time, time to peak and input resistance increased as temperature was lowered, whereas resting potential was diminished. When compared at their growth temperatures and most intermediate temperatures, the value of the various parameters monitored were generally different for the two cultures. The Q10 value for resting potential changes of Tg 20 degrees C cells about 20 degrees C was 1.20. As in T. vorax this was significantly (P less than 0.01) greater than that predicted for a diffusion potential and suggested that T. pyriformis--NT1 may have an electrogenic pump component in its membrane potential.