Auditory evoked BOLD responses in awake compared to lightly anaesthetized zebra finches.

Functional magnetic resonance imaging (fMRI) is increasingly used in cognitive neuroscience and has become a valuable tool in the study of auditory processing in zebra finches, a well-established model of learned vocal communication. Due to its sensitivity to head motion, most fMRI studies in animals are performed in anaesthetized conditions, which might significantly impact neural activity evoked by stimuli and cognitive tasks. In this study, we (1) demonstrate the feasibility of fMRI in awake zebra finches and (2) explore how light anaesthesia regimes affect auditory-evoked BOLD responses to biologically relevant songs. After an acclimation procedure, we show that fMRI can be successfully performed during wakefulness, enabling the detection of reproducible BOLD responses to sound. Additionally, two light anaesthesia protocols were tested (isoflurane and a combination of medetomidine and isoflurane), of which isoflurane alone appeared to be the most promising given the high success rate, non-invasive induction, and quick recovery. By comparing auditory evoked BOLD responses in awake versus lightly anaesthetized conditions, we observed overall effects of anaesthetics on cerebrovascular reactivity as reflected in the extent of positive and negative BOLD responses. Further, our results indicate that light anaesthesia has limited effects on selective BOLD responses to natural versus synthetic sounds.

Ultrasound-mediated intracellular drug delivery using microbubbles and temperature-sensitive liposomes.

A novel two-step protocol for intracellular drug delivery has been evaluated in vitro. As a first step TO-PRO-3 (a cell-impermeable dye that displays a strong fluorescence enhancement upon binding to nucleic acids) encapsulated in thermosensitive liposomes was released after heating to 42°C. A second step consisted of ultrasound-mediated local permeabilization of cell membrane allowing TO-PRO-3 internalization observable as nuclear staining. Only the combination of two consecutive steps - heating and sonication in the presence of SonoVue microbubbles led to the model drug TO-PRO-3 release from the thermosensitive liposomes and its intracellular uptake. This protocol is potentially beneficial for the intracellular delivery of cell impermeable drugs that suffer from rapid clearance and/or degradation in blood and are not intrinsically taken up by cells.