Background The mechanism by which anaesthetic agents produce general anaesthesia is not yet fully understood. Retraction of neurites is an important function of individual neurones and neural plexuses during normal and pathological conditions, and it has been shown that such a retraction pathway exists in developing and mature neurones. We hypothesized that propofol decreases neuronal activity by causing retraction of neuronal neurites.

Methods Primary cultures of rat cortical neurones were exposed in concentration– and time–response experiments to 0.02, 0.2, 2, and 20 µM propofol or lipid vehicle. Neurones were pretreated with the GABA_A receptor (GABA_AR) antagonist, bicuculline, the myosin II ATPase activity inhibitor, blebbistatin, and the F-actin stabilizing agent, phalloidin, followed by administration of propofol (20 µM). Changes in neurite retraction were evaluated using time-lapse light microscopy.

Results Propofol caused a concentration- and time-dependent reversible retraction of cultured cortical neurone neurites. Bicuculline, blebbistatin, and phalloidin completely inhibited propofol-induced neurite retraction. Images of retracted neurites were characterized by a retraction bulb and a thin trailing membrane remnant.

Conclusions Cultured cortical rat neurones retract their neurites after exposure to propofol in a concentration- and time-dependent manner. This retraction is GABA_AR mediated, reversible, and dependent on actin and myosin II. Furthermore, the concentrations and times to full retraction and recovery correspond to those observed during propofol anaesthesia.

Neuronal intracellular transport is performed by motor proteins, which deliver vesicles, organelles and proteins along cytoskeletal tracks inside the neuron. We have previously shown that the anesthetic propofol causes dose- and time-dependent, reversible retraction of neuronal neurites. We hypothesize that propofol alters the vesicular transport of cortical neurons due to this neurite retraction. Primary cultures of co-cultivated rat cortical neurons and glial cells were exposed to either 2 mu M propofol, control medium or the lipid vehicle, in time-response experiments. Reversibility was tested by washing propofol off the cells. The role of the GABA(A) receptor (GABA(A)R) was assessed with the GABA(A)R antagonist gabazine. Vesicles were tracked using differential interference contrast video microscopy. Propofol caused a retrograde movement in 83.4 +/- 5.2% (mean +/- S.E.M.) of vesicles, which accelerated over the observed time course (0.025 +/- 0.012 mu m.s(-1)). In control medium, vesicles moved predominantly anterograde (84.6 +/- 11.1%) with lower velocity (0.011 +/- 0.004 mu m.s(-1)). Cells exposed to the lipid vehicle showed the same dynamic characteristics as cells in control medium. The propofol-induced effect on vesicle transport was reversible and blocked by the GABA(A)R antagonist gabazine in low concentration. Our results show that propofol causes a reversible, accelerating vesicle movement toward the neuronal cell body that is mediated via synaptic GABA(A)R. We have previously reported that propofol initiates neurite retraction, and we propose that propofol causes vesicle movement by retrograde flow of cytoplasm from the narrowed neurite.

Background: Orexin A (OA) is an endogenous peptide regulating awakeness. It is a potential reversing agent of anaesthetics, shown to reduce anaesthesia in animals, but on cellular level its mechanisms are unknown.

Methods: Primary cortical cell cultures from newborn rat brains are used, and live cell light microscopy is performed to measure 1) neurite retraction after propofol, thiopental, barbituric acid and ketamine exposure and 2) the effect of OA application either before or after anaesthetics. Cytoskeletal reorganization of vimentin and actin is evaluated with fluorescence microscopy, protein changes detected with Western blot and proteins identified with mass spectrometry after treatment with anaesthetics and/or OA.

Results: Orexin A reverses and inhibits neurite retraction and the actin ring formation induced by propofol and thiopental. No effect on retraction or actin rings was seen for ketamine (not active on GABA_A receptors), the non-anaesthetic barbituric acid, OA or solvents used. OA increases tyrosine phosphorylation of a 50 kDa protein, identified as vimentin. Propofol treatment induces a granular appearance of vimentin, which OA reverses to a smooth distribution throughout the cell.

Conclusions: OA reverses cellular effects known to be mediated via the GABA_A receptor of both propofol and thiopental in cultured rat brain cells. The morphologic changes of actin and vimentin caused by propofol and thiopental, and the subsequent reversal by OA, deepens our understanding of the mechanisms of anaesthesia. In the future, an OA agonist could be used to reverse the effects of GABA_A receptor dependent anaesthetic drugs.

Background: Propofol retracts neurites and reverses the transport of vesicles in rat cortical neurons in a γ-aminobutyric acid type A (GABA_A) receptor dependent manner. Orexin A (OA) is an endogenous peptide regulating wakefulness, and is known to interact with anaesthetics. We aim to investigate whether OA inhibits propofol-induced neurite retraction and elucidate the intracellular signalling involved.

Methods: In primary cortical cell cultures from newborn rat brains, live cell light microscopy was used to measure neurite retraction after propofol (2 μM) with or without OA (10 nM) application after preincubation with the Rhokinase inhibitor (HA-1077), phospholipase D (PLD) inhibitor [5-fluoro-2- indolyl des-chlorohalopemide (FIPI)], protein kinase C (PKC) inhibitor (staurosporine) or PKC activator phorbol 12-myristate 13-acetate (PMA).

Results: The neurite retraction induced by propofol is blocked by HA-1077 and PMA. OA blocks neurite retraction induced by propofol, and this inhibitory effect could be prevented by FIPI, as well as staurosporine.

Conclusions: Rho-kinase is essential for propofol-induced neurite retraction in cortical neuronal cells. Activation of PKC plays an inhibitive role during neurite retraction caused by propofol. OA blocks propofol-induced neurite retraction by a PLD/PKC-mediated pathway.