Abstract
Cessation of one-week oral administration of the benzodiazepine flurazepam (FZP) to rats results in withdrawal anxiety after 1 day of withdrawal. FZP withdrawal is correlated with synaptic incorporation of homomeric GluA1-containing α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) in the proximal stratum radiatum of CA1 neurons. After 2 days of withdrawal, Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylates GluA1 subunits at Ser831, increasing channel conductance. Secondary to AMPAR potentiation, GluN2B-containing N-methyl-D-aspartate receptors (NMDARs), known binding partners of CaMKII, are selectively removed from the postsynaptic density (PSD). While activation of synaptic CaMKII is known to involve translocation to the PSD, CaMKII bound to NMDARs may be removed from the PSD. To distinguish these possibilities, the current studies used postembedding immunogold electron microscopy to investigate alterations in CaMKII signaling at CA1 stratum radiatum synapses after 2 days of FZP withdrawal. These studies revealed decreased total, but not autophosphorylated (Thr286) CaMKIIα expression in CA1 PSDs. The removal of CaMKII-GluN2B complexes from the PSD during drug withdrawal may serve as a homeostatic mechanism to limit AMPAR-mediated CA1 neuron hyperexcitability and benzodiazepine withdrawal anxiety.
Highlights
Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a dodecameric holoenzyme composed of a combination of four enzyme isoforms (α, β, γ, or δ), though α and β are the primary isoforms expressed in neurons [1]
Prior evidence suggests that in rats withdrawn from FZP for 2 days, CaMKII may be activated by Ca2+ influx through L-type voltage-gated Ca2+ channels (L-VGCCs) to phosphorylate GluA1 subunits at Ser831 increasing α-Amino-3-hydroxy-5-methyl-4isoxazolepropionic acid receptor (AMPAR) conductance [11, 13, 19, 34]
Cross-reaction of the goat antimouse secondary antibody conjugated to 15 nm gold with the opposite primary was tested by replacement of the monoclonal anti-CaMKIIα antibody with the polyclonal anti-pCaMKII antibody, which yielded no pre- or postsynaptic 15 nm immunogold particles within 60 randomly selected asymmetric synaptic profiles
Summary
Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a dodecameric holoenzyme composed of a combination of four enzyme isoforms (α, β, γ, or δ), though α and β are the primary isoforms expressed in neurons [1]. CaMKII molecules within the holoenzyme autophosphorylate adjacent enzymes at Thr286 (or Thr287 in non-α isoforms) during persistent activation by Ca2+/CaM [2], leading to autonomous, Ca2+-independent CaMKII activity [3]. This feature allows CaMKII to maintain a molecular memory of recent neuronal activity and is a critical component of activity-dependent long-term potentiation (LTP), a form of synaptic plasticity in hippocampal CA1 neurons thought to underlie learning and memory [4]. CaMKII activation during LTP is dependent on NMDAR-mediated Ca2+ influx, whereas L-type voltage-gated Ca2+ channels (L-VGCCs) may activate CaMKII in nucleus accumbens following chronic cocaine exposure [9, 10]. While L-VGCCs are potentiated in CA1 neurons after withdrawal from benzodiazepines and may initiate CaMKIImediated potentiation of AMPARs [11,12,13], the mechanisms of CaMKII signaling during benzodiazepine withdrawal remain unknown
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
