Recent studies have shown that the survival of mammalian motoneurons in vitro is promoted by neurotrophins (NTs) and cAMP. There is also evidence that neurotrophins enhance transmitter release. We thus investigated whether these agents also promote synaptogenesis. Cultured Xenopus spinal cord neurons were treated with a mixture of BDNF, glia-derived neurotrophic factor, NT-3, and NT-4, in addition to forskolin and IBMX or the cell-permeant form of cAMP, to elevate the cAMP level. The outgrowth and survival of neurons were dramatically increased by this trophic stimulation. However, when these neurons were cocultured with muscle cells, the trophic agents resulted in a failure of synaptogenesis. Specifically, the induction of ACh receptor (AChR) clustering in cultured muscle cells was inhibited at nerve-muscle contacts, in sharp contrast to control, untreated cocultures. Because AChR clustering induced by agrin or growth factor-coated beads in muscle cells was unaffected by trophic stimulation, its effect on synaptogenesis is presynaptic in origin. In the control, agrin was deposited along the neurite and at nerve-muscle contacts. This was significantly downregulated in cultures treated with trophic stimuli. Reverse transcriptase-PCR analyses showed that this decrease in agrin deposition was caused by an inhibition of agrin synthesis by trophic stimuli. Both agrin synthesis and induction of AChR clustering were restored under trophic stimulation when Schwann cell-conditioned medium was introduced. These results suggest that trophic stimulation maintains spinal neurons in the growth state, and Schwann cell-derived factors allow them to switch to the synaptogenic state.

This paper presents the design, fabrication, dynamic analysis, and experimental results of an efficient resonantly-driven piezoelectric micropump. The micropump consists of a folded vibrator, two polydimethylsiloxane (PDMS) check valves and compressible spaces. A newly developed folded vibrator with piezoelectric sheets serves as the resonantly-driven actuator. The vibrator provides uniform strain distribution in piezoelectric sheets surfaces to improve their utilizing efficiency. The PDMS check valves used in this design increase pump’s working stability and largely reduce the leakage rate. In addition, the performance of the micropump is significantly improved by two compressible spaces near the check valves. Experimental results on a prototype with dimensions of 20 mm × 20 mm × 28 mm demonstrate that the maximum flow rate of 118 ml min−1 and maximum back pressure of 22.5 kPa are obtained when the micropump is driven by a sinusoidal voltage of 120 Vpp at 361 Hz. A stable minimum flow rate of 160 μl min−1 can be obtained with driving voltage of 4 Vpp. The maximum power consumption of the micropump is approximately 62 mW for 118 ml min−1 at zero backpressure.

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