Differential association of phosphatases with hematopoietic co-receptors bearing immunoreceptor tyrosine-based inhibition motifs

A novel family of inhibitory co-receptors has been recently defined according to the presence in their intracytoplasmic domain of immunoreceptor tyrosine-based inhibition motifs (ITIM). In particular, this family includes a low-affinity receptor for IgG, FcγRIIB, which is widely expressed on hematopoietic cells, as well as killer cell inhibitory receptors (KIR) for major histocompatibility complex (MHC) class I proteins, expressed on both T and natural killer (NK) lymphocytes. FcγRIIB and KIR inhibitory function depends upon the tyrosine phosphorylation of their respective ITIM. Phosphorylated FcγRIIB and KIR ITIM bind the tandem SH2 tyrosine phosphatases, SHP-1 and SHP-2. Recently, FcγRIIB has been shown to associate with a polyphosphate inositol 5-phosphatase, SHIP, which appears to be involved in its inhibitory function. Using cell lysate adsorption to phosphorylated ITIM peptides and surface plasmon resonance, we demonstrate here that, in contrast to FcγRIIB, KIR (CD158b: p58.2) do not bind to SHIP, and only recruit SHP-1 and SHP-2. In addition, we show that point mutation of the amino acid residue in position tyrosine-2 of FcγRIIB and KIR ITIM abolihes their binding to SHP-1 and SHP-2, but leaves intact the association of SHIP with FcγRIIB ITIM. These data contribute to the structural definition of ITIM and document a differential recruitment of phosphatases by distinct ITIM. These findings also reveal that diverse strategies of inhibition are used by distinct members of the ITIM-bearing co-receptor family.     

Effects of L-DOPA and L-5-HTP on the visual evoked response

Small doses (10 and 20 mg/kg) of L-DOPA inhibited the amplitude of the visual evoked response (VER), while large doses (40 and 80 mg/kg) enhanced it. Though low doses (12.5 and 25 mg/kg) of L-5-HTP caused a slight increase in amplitude of the VER, the simultaneous administration of 12.5 mg/kg of L-5-HTP and 10 mg/kg of L-DOPA produced a marked enhancement. The peak latency was prolonged after the injection of any doses of L-DOPA, L-5-HTP, or both.     

Faster acquisition of an olfactory discrimination following septal lesions in male albino rats.

Normal rats and rats with septal lesions were maintained on a 23.5-hr water deprivation schedule and trained to bar press for water reinforcement, which was available during the presentation of one odor (SD) but not another (Sdelta). Vanilla and vinegar were the olfactants. Both groups showed evidence of discrimination within the first 2-hr of training and reached asymptotic discrimination ratios greater than 90 percent, but the rats with septal lesions reached successively higher levels of discrimination faster than the controls. The results suggest a septal inhibitory influence on the olfactory bulbs.     

Inhibition des activités spinales à caractère locomoteur par une modalité particulière de stimulation somatique chez le lapin

Summary In decerebrate rabbit preparations, a gentle pressure exerted on the dorsal skin area can completely suppress the rhythmic, locomotor-like movements or the corresponding nerve discharges which easily develop in such preparations. This inhibition can also be obtained on spinal preparation (and thus does not depend upon supraspinal levels); its maximal effect (i.e. minimal pressure threshold) is located at the lumbar level. It involves tonic receptors belonging both to the skin and to muscle and/or joints. This phenomenon probably plays a role in the so-called hypnotic akinesia which, as is well known, can easily be elicited in rabbits put in dorsal decubitus.

Notes de Remerciements. Travail réalisé avec l'aide d'une subvention du C.N.R.S. (ERA 411), de l'I.N.S.E.R.M. (Contrat 71 11 64) et de la Fondation pour la Recherche médicale française.     

Habituation of the startle response in adrenalectomized rats

In a series of three experiments adrenalectomized, sham-operated and non-operated rats (N = 15) were presented with 27 tones at each of three intensities on two successive days or 60 tones at a 60 sec interstimulus interval with each tone being followed by another tone either 2, 4, 8 or 16 sec later, or 50 tones at a 30 sec interstimulus interval on each of five successive days. All groups had equivalent initial startle amplitudes and showed equivalent rates of response decrement at each test intensity and each interstimulus interval as well as over successive days of exposure. The results indicate that the adrenal glands are not crucial for habituation of the acoustic startle response and suggest that those aspects of stress adaptation that require an intact adrenal-pituitary system are not important for habituation of the startle.     

Skin Conductance Response Conditioning with High CS Intensities: Additional Evidence with New Controls

In an effort to determine whether or not conditioning is possible when CS intensity is at least as high as US intensity, nine groups of human subjects were employed in a skin conductance conditioning study. White noise CS and US intensities of 95- and 115-dB were varied orthogonally in the experimental groups, while control groups were incorporated to control for overall signal frequency and differences in habituation rates attributable to differences in intertrial interval. By conventional contrasts first interval response (FIR) conditioning was observed, but when controls for differential habituation rates were incorporated in the contrasts there was no evidence of FIR conditioning. Second interval response (SIR) conditioning was obtained, but it was manifest as an anticipatory response to the higher of two US intensities rather than in conventional conditioning vs control group comparisons. It was also shown that high CS intensities induce suppression of SIR levels, with greater suppression associated with the higher intensity. Several conclusions were made: 1) in a simple trace conditioning paradigm with skin conductance responding as the measure, it is not clear that what we have typically called a conditioning effect is separable from an habituation effect; 2) conditioning is possible even when CS intensity is as high as or higher than US intensity; and 3) the use of time sample measurement in the absence of signals provides a useful baseline for determining overall increases and decreases in SIR level.     

Reticulospinal actions on primary afferent depolarization of cutaneous and muscle afferents in the isolated frog neuraxis

The effects of the brainstem reticular formation on the intraspinal excitability of low threshold cutaneous and muscle afferents were studied in the frog neuraxis isolated together with the right hindlimb nerves. Stimulation of low threshold fibers (less than two times threshold) in cutaneous nerves produced short latency, negative field potentials in the ipsilateral dorsal neuropil (200–400 m depth) that reversed to positivity at deeper regions (500–700 m). Stimulation of low threshold fibers (less than two times threshold) in muscle nerves produced, instead, negative responses that acquired their maximum amplitude in the ventral neuropil (700–900 m depth). These electrophysiological findings suggest, in agreement with observations in the cat, that low threshold cutaneous and muscle afferents end at different sites in the spinal cord. Intraspinal microstimulation applied within the dorsal neuropil produced antidromic responses in low threshold cutaneous afferents that were increased in size following stimulation of the dorsal or ventral roots, as well as of the brainstem reticular formation. This increase in excitability is interpreted as being due to primary afferent depolarization (PAD) of the intraspinal terminals of cutaneous fibers. Antidromic responses recorded in muscle nerves following intraspinal stimulation within the ventral neuropil were also increased following conditioning stimulation of adjacent dorsal or ventral roots. However, stimulation of the bulbar reticular formation produced practically no changes in the antidromic responses, but was able to inhibit the PAD of low threshold muscle afferents elicited by stimulation of the dorsal or ventral roots. It is suggested that the PAD of low threshold cutaneous and muscle afferents is mediated by independent sets of interneurons. Reticulospinal fibers would have excitatory connections with the interneurons mediating the PAD of cutaneous fibers and inhibitory connections with the interneurons mediating the PAD of muscle afferents. Although our results provide no direct information on whether the reticulospinal depression of the PAD elicited in low threshold muscle afferents is due to inhibition along the pathways producing PAD of muscle spindle or of tendon organ afferents, it seems likely — by analogy with what has been seen in the cat spinal cord — that these inhibitory actions are mostly restricted to the pathways producing PAD in the terminal arborizations of muscle spindle afferents. These results emphasize the specificity of the descending control of the synaptic efficacy of low threshold cutaneous and muscle afferents which could be of importance for motor performance.     

Inhibition of anti-GD3-ganglioside antibody-induced proliferation of human CD8+ T cells by CD16+ natural killer cells

The ganglioside GD3 has been described as a membrane component of human T cells which is involved in T cell growth. In the present study the activating function of GD3 for human CD4⁺ and CD8⁺ T cells was analyzed by five different monoclonal antibodies (mAb) directed against the GD3 molecule. Three mAb U5, Z21 and R24 induced strong proliferation of peripheral blood mononuclear cells and purified CD8⁺ and CD4⁺ T cells of normal donors containing less than 5% CD16⁺ natural killer (NK) cells. In contrast to CD4⁺ T cells, CD8⁺ T cells proliferated only weakly in the presence of 15% CD16⁺ NK cells. The proliferative response of purified CD4⁺ and CD8⁺ T cells (<5% NK cells) correlated with the antibody-dependent induction of integral and soluble interleukin-2 (IL-2) receptors and was reduced to 20% by an anti-IL-2 receptor antibody. Our results show, that the GD3 molecule represents an activation molecule for both CD4⁺ and CD8⁺ T cells and that CD16⁺ NK cells selectively inhibit anti-GD3 antibody-induced proliferation of CD8⁺ T cells.     

Local circuit neurons in both the dentate gyrus and Ammon's horn establish synaptic connections with principal neurons in five day old rats: a morphological basis for inhibition in early development

Summary Glutamate decarboxylase (GAD)-positive and Golgi impregnated local circuit neurons of the hippocampal formation of five day old rats were examined in light and electron microscopic preparations. The ultrastructural features of these neurons were similar in both the dentate gyrus and CA1 area of Ammon's horn. Somata displayed a perikaryal cytoplasm rich in organelles but lacked organized Nissl bodies. Most nuclei showed intranuclear infoldings of varying degrees but no intranuclear sheets or rods were found. Somata and dendrites were contacted by relatively immature axon terminals that formed mainly symmetric synapses. The axons of local circuit neurons in both the dentate gyrus and Ammon's horn formed symmetric synapses with somata and dendrites of the principal neurons in these regions. Thus, both GAD-positive and Golgi-impregnated terminals of local circuit neurons were observed to form synapses with pyramidal and granule cells. These terminals were usually small and contained relatively few pleomorphic synaptic vesicles. The results show that a circuitry for inhibition is established in the 5 day old dentate gyrus and Ammon's horn, even though the local circuit neurons lack some of the typical adult ultrastructural features at this age.     

Intracortical inhibition of lower limb motor-evoked potentials after paired transcranial magnetic stimulation

The aim of the present study was to determine the characteristics of intracortical inhibition in the motor cortex areas representing lower limb muscles using paired transcranial magnetic (TMS) and transcranial electrical stimulation (TES) in healthy subjects. In the first paradigm (n=8), paired magnetic stimuli were delivered through a double cone coil and motor evoked potentials (MEPs) were recorded from quadriceps (Q) and tibialis anterior (TA) muscles during relaxation. The conditioning stimulus strength was 5% of the maximum stimulator output below the threshold MEP evoked during weak voluntary contraction of TA (33±5%). The test stimulus (67±2%) was 10% of the stimulator output above the MEP threshold in the relaxed TA. Interstimulus intervals (ISIs) from 1–15 ms were examined. Conditioned TA MEPs were significantly suppressed (P<0.01) at ISIs of less than 5 ms (relative amplitude from 20–50% of the control). TA MEPs tended to be only slightly facilitated at 9-ms and 10-ms ISIs. The degree of MEP suppression was not different between right and left TA muscles despite the significant difference in size of the control responses (P<0.001). Also, conditioned MEPs were not significantly different between Q and TA. The time course of TA MEP suppression, using electrical test stimuli, was similar to that found using TMS. In the second paradigm (n=2), the suppression of TA MEPs at 2, 3, and 4 ms ISIs was examined at three conditioning intensities with the test stimulation kept constant. For the pooled 2- to 4-ms ISI data, relative amplitudes were 34±6%, 61±5%, and 98±9% for conditioning intensities of 0.95, 0.90, and 0.85× active threshold, respectively (P<0.01). In conclusion, the suppression of lower limb MEPs following paired TMS showed similar characteristics to the intracortical inhibition previously described for the hand motor area. Received: 21 June 1996 / Accepted: 23 May 1997