Anesthetic Treatment Blocks Synaptogenesis But Not Neuronal Regeneration of CulturedLymnaeaNeurons

Abstract

Trauma and injury necessitate the use of various surgical interventions, yet such procedures themselves are invasive and often interrupt synaptic communications in the nervous system. Because anesthesia is required during surgery, it is important to determine whether long-term exposure of injured nervous tissue to anesthetics is detrimental to regeneration of neuronal processes and synaptic connections. In this study, using identified molluscan neurons, we provide direct evidence that the anesthetic propofol blocks cholinergic synaptic transmission between soma-soma paired Lymnaea neurons in a dose-dependent and reversible manner. These effects do not involve presynaptic secretory machinery, but rather postsynaptic acetylcholine receptors were affected by the anesthetic. Moreover, we discovered that long-term (18-24 h) anesthetic treatment of soma-soma paired neurons blocked synaptogenesis between these cells. However, after several hours of anesthetic washout, synapses developed between the neurons in a manner similar to that seen in vivo. Long-term anesthetic treatment of the identified neurons visceral dorsal 4 (VD4) and left pedal dorsal 1 (LPeD1) and the electrically coupled Pedal A cluster neurons (PeA) did not affect nerve regeneration in cell culture as the neurons continued to exhibit extensive neurite outgrowth. However, these sprouted neurons failed to develop chemical (VD4 and LPeD1) and electrical (PeA) synapses as observed in their control counterparts. After drug washout, appropriate synapses did reform between the cells, although this synaptogenesis required several days. Taken together, this study provides the first direct evidence that the clinically used anesthetic propofol does not affect nerve regeneration. However, the formation of both chemical and electrical synapses is severely compromised in the presence of this drug. This study emphasizes the importance of short-term anesthetic treatment, which may be critical for the restoration of synaptic connections between injured neurons.

Neonicotinoid insecticides inhibit cholinergic neurotransmission in a molluscan (Lymnaea stagnalis) nervous system

“…The cholinergic nature of the VD4 -RPeD1 synapse has previously been established (Woodin et al, 2002;Xu et al, 2009). Our experiments confirmed the involvement of nicotinergic ACh receptors in the monosynaptic excitatory component of the VD4 evoked synaptic responses on the RPeD1 neuron, by the almost complete (up to 90 %) inhibition of the sEPSP amplitudes in 50 µM d-tubocurarine applied in the bath (Fig.…”

“…Both connections have also been shown to re-form between the isolated neurons when placed in culture conditions (Syed et al, 1990;Hamakawa et al, 1999). The first, excitatory component of these monosynaptic connections provides a suitable in vitro model while studying synaptogenesis (Feng et al, 1997;Woodin et al, 2002), or toxin-induced alterations of cholinergic neurotransmission (Woodall et al, 2003;Onizuka et al, 2012).…”

Anesthesia in oysters of the genus Crassostrea cultured in Brazil

“…It is important to highlight that prolonged exposure to the anaesthetic can be lethal (WOODALL et al, 2003) for molluscs. These authors recommend short-term anaesthetic treatment, to ensure restoration of synaptic connections between injured neurons.…”

Transient electrical coupling regulates formation of neuronal networks

“…In developing leech embryos, intrinsic abilities to extend axons that project bilaterally are inhibited in an agedependent fashion that is likely mediated by gap-junctional communication (Wolszon et al, 1995). Still, anesthetic treatment that blocks synaptogenesis among cultured Lymnaea neurons had no effect on neurite extension, indicating that synapse formation and neuritic outgrowth can be dissociated (Woodall et al, 2003).…”