Physical and physiological characteristics of micropressure ejection of drugs from multibarreled pipettes

The micropressure ejection technique was characterized in vivo as well as in vitro. Volumes of radiolabelled drug released from multibarreled pipettes by this method increased linearly with increasing ejection pressure or time. This was reflected in vivo by graded inhibitions of cortical cell activity with increasing ejection pressures of enkephalin. The linearity of this response was independent of interejection time, suggesting that there is no warm-up phenomenon with the micropressure ejection technique. In vitro, interejection times did not affect the amount of 3H-sucrose released by micropressure ejection. The volume of drug released by micropressure ejection was highly reproducible. Likewise, the responses of cerebellar Purkinje cells to repeated pressure applications of norepinephrine or GABA were uniform over long periods of time. The variability in drug release between two barrels of a multibarreled pipette, or between two pipettes using micropressure ejection, was also considerably less than that observed with microiontophoresis. In addition to the linearity and reproducibility of micropressure ejection, these studies demonstrate that substances which are difficult to apply by iontophoresis, such as peptides, are readily applied by this method.