Differential regulation of beta-arrestin 1 and beta-arrestin 2 gene expression in rat brain by morphine

Beta-arrestins are a family of regulatory and scaffold proteins functioning in signal transduction of G protein-coupled receptors including opioid receptors. Upon agonist stimulation, beta-arrestins bind to opioid receptors phosphorylated by G protein-coupled receptor kinases and promote receptor internalization and desensitization. Studies indicated that beta-arrestins are required in the development of morphine tolerance in mice. In the current study, we investigated the potential regulatory effects of morphine administration on beta-arrestin 1 and beta-arrestin 2 mRNA levels in different brain regions in rat using in situ hybridization method. Our results showed that the acute morphine administration (10 mg/kg) resulted in approximately 30% reduction in both beta-arrestin 1 and beta-arrestin 2 mRNA levels in hippocampus while the chronic morphine treatment (10 mg/kg, b.i.d., for 9 days) caused no significant change in level of either beta-arrestin mRNA. In locus coeruleus, both acute and chronic morphine treatments resulted in significant decreases (over 50%) in beta-arrestin 1 mRNA level but failed to induce any change in the level of beta-arrestin 2 gene expression. The acute morphine administration had no significant effect on beta-arrestin 1 or beta-arrestin 2 mRNA level in periaqueductal gray and cerebral cortex. However, after chronic morphine treatment, beta-arrestin 2 mRNA level decreased by 40% in periaqueductal gray and increased by 25% in cerebral cortex, in strong contrast to the unchanged beta-arrestin 1 mRNA level in these two brain regions. Furthermore, spontaneous or naloxone-precipitated withdrawal of morphine that did not affect the level of beta-arrestin 1 mRNA resulted in an aberrant increase (100% over control) in beta-arrestin 2 mRNA level in hippocampus. Our results thus demonstrated for the first time that opiate administration regulates level of beta-arrestin mRNAs in brain and the expression of beta-arrestin 1 and beta-arrestin 2 subtypes is differentially regulated in locus coeruleus, periaqueductal gray, and cerebral cortex by morphine. These data suggest that beta-arrestin 1 and beta-arrestin 2 may play different roles in the development of opioid tolerance and dependence.

Observation of exotic meson production in the reaction pi- p --> eta'pi- p at 18 GeV/c

An amplitude analysis of an exclusive sample of 5765 events from the reaction pi- p-->eta'pi- p at 18 GeV/c is described. The eta'pi- production is dominated by natural parity exchange and by three partial waves: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a2(1320) meson as well as the a4(2040) meson, observed for the first time decaying to eta'pi-. The dominant, exotic (non- qq) 1(-+) partial wave is shown to be resonant with a mass of 1.597+/-0.010(+0.045)(-0.010) GeV/c2 and a width of 0.340+/-0.040+/-0.050 GeV/c2. This exotic state, the pi1(1600), is produced with a t dependence which is different from that of the a2(1320) meson, indicating differences between the production mechanisms for the two states.

[Effects of muscle spindle afferents on the regulation of respiration in rabbit]

Effect of muscle spindle afferent invoked by intraarterial injection of succinylcholine (Sch) on respiration was assessed by changes in unit discharge of respiration related neurons and phrenic nerve of 63 anesthetized, bilaterally vagotomized and artificially ventilated rabbits. The results are as follows. (1) Intra~arterial injection of Sch prolonged inspiratory duration (Ti) or decreased expiratory duration (Te) and augmented respiratory frequency (RF). (2) 66% (37/56) of the medullary inspiratory neurons were excited and 10/17 of the expiratory neurons were inhibited by intraarterial injection of Sch, reaching maximum respectively at 1 2 and 2 3 min after injection, while non-respiration related neurons were not affected. (3) This effect of Sch was suppressed or abolished when muscle spindles were destroyed by intramuscular injection of bupivacaine.

Effects of simulated microgravity on immunoreactivity of conjugated-ubiquitin of muscle spindles of soleus in rats

It is well known that the muscle spindle is a receptor of muscle's tension and length, it plays an important role in maintaining the muscle's tension. The aim of the present study is to compare the cross-section area (CSA) and the immunoreactivity of conjugated-ubiquitin in soleus extrafusal and intrafusal fibers after simulated-microgravity in order to demonstrate the role of muscle spindle in muscle atrophy induced by simulated microgravity.

[Role of red nucleus in inhibiting nociceptive responses of rat spindle afferent]

Using extracellular recording techniques, the effect of excitation of red nucleus (RN) on C-responses of wide dynamic range (WDR) neurons and the roles of RN in the inhibitory effect of spindle afferent activated by succinycholine (SCH) on C-responses of WDR neurons were studied. Stimulation of RN caused a significant reduction of nociceptive responses of WDR neurons, which was significantly attenuated by intravenous cyproheptadine and contralateral lesion of RN. These results suggest that the inhibitory effect on nociceptive responses of WDR neurons caused by RN stimulation was partly mediated by 5-HT and RN plays an important role in analgesia induced by the muscle spindle afferent activity.

Reversal of the static component of spindle potential by imposed depolarizing current in the frog muscle spindle

The static component of the spindle potential provoked during stretch of isolated muscle spindles of the frog was reversed during the application of depolarizing currents ranging from 0.2 to 5 nA in normal Ringer solution and also in Na+-free Ringer solution. In the same range of current intensities, spontaneous rhythmic hyperpolarizations due to [Ca2+]i-activated GK, an attenuation of membrane impedance, and an anomalous decrease in amplitude of the afferent spikes were observed. All 4 phenomena were abolished by K+ channel blockers (10 mM CsCl, 1-2 mM 4-aminopyridine (4-AP), or 20 mM tetraethylammonium chloride (TEA], Ca2+ channel blockers (5-10 mM CoCl2, MnCl2, 1-2 mM CdCl2 or 0.5 mM verapamil) or 0.1 mM quinine. The amplitude of the static component of the spindle potential was markedly increased at threshold concentration of the K+ channel blockers (5 mM CsCl, 0.1-0.5 mM 4-AP or 5-10 mM TEA), but the component disappeared at that of the Ca2+ channel blockers. The rhythmic hyperpolarizations are associated with the spindle potential, except for its dynamic component, which often triggers a hyperpolarizing deflection. We suggest that both the static component of the spindle potential and rhythmic hyperpolarizations are due to GK(Ca) in the intracapsular axon, either along the terminal or at the branching nodes, or both; and that the receptor potential contributes to, but is not the same as, the spindle potential.