Pairing the cholinergic agonist carbachol with patterned Schaffer collateral stimulation initiates protein synthesis in hippocampal CA1 pyramidal cell dendrites via a muscarinic, NMDA-dependent mechanism

Abstract

Effects of afferent stimulation on local synthesis of protein in CA1 pyramidal cell dendrites were studied using light microscope autoradiography. Tissue was fixed with paraformaldehyde immediately after 3 min exposure to 3H-leucine in order to trap 3H associated with macromolecules. The rate of 3H-leucine incorporation into dendrites of resting hippocampal slices was 10% the rate of incorporation into cell somata. Ninety percent of the incorporation into the somata was inhibited by cycloheximide (300 microM); none of the incorporation into dendrites was blocked by cycloheximide. Thus, there is no measurable extramitochondrial synthesis of protein in the dendrites of the resting slice. Slices were exposed to 50 microM carbachol and the Schaffer collateral afferents to the CA1 pyramidal cells were stimulated intermittently at 10 Hz over a 20 min period. In this case, 3H incorporation into dendrites was increased almost threefold over resting levels, with no effect on label over the cell somata. There was no associated increase in uptake of free 3H-leucine, and the increase in label was completely blocked by cycloheximide. Thus, associating carbachol and afferent stimulation appears to activate de novo protein synthesis in the dendrites. Neither the carbachol alone nor the Schaffer collateral stimulation alone increased synthesis. The activation of dendrite synthesis was completely blocked by 5 microM atropine, and also by 50 microM D-aminophosphonovalerate. It did not occur when carbachol was paired with steady stimulation of the Schaffer collaterals at 1 Hz for 20 min, rather than with the patterned high-frequency stimulation. Thus, associating a cholinergic agonist with a level of neural activity that occurs in CA3 and CA1 pyramidal cells during exploratory behavior (Muller et al., 1987) initiates local protein synthesis in target dendrites. This effect is dependent on muscarinic cholinergic receptors and NMDA-type glutamate receptors. The possible relationship of this phenomenon to mechanisms of learning is discussed.

γ-Aminobutyric acid type A receptors modulate cAMP-mediated long-term potentiation and long-term depression at monosynaptic CA3–CA1 synapses

“…In fact, a late phase protein-synthesis-dependent LTD in hippocampal slice cultures has been reported (25). Nevertheless, we cannot rule out the possibility that LTD induced by concurrent application of Sp-cAMPS and picrotoxin may include an early phase of LTD that requires protein synthesis, presumably locally and within 30 min after the drug treatment (26)(27)(28).…”

Repeated confocal imaging of individual dendritic spines in the living hippocampal slice: evidence for changes in length and orientation associated with chemically induced LTP

“…Recently, it has been found that such dendritic protein synthesis may be activated by afferent stimulation: 3H-leucine incorporation in CA1 dendrites is induced immediately after high frequency, but not low frequency, stimulation of Schaffer collaterals in the presence of carbachol (Feig and Lipton, 1993); label incorporation is blocked by D-aminophosphonovalerate and also by atropine.…”

Protein synthesis in the dendrite

“…For example, the induction of LTP at Schaffer collateral-CA1 synapses induced the synthesis of secretory proteins (Duffy et al 1981;Lauri et al 1996). In addition, lowfrequency (10 Hz) stimulation of hippocampal slices treated with the cholinergic agonist carbachol can induce new protein synthesis in dendrites (Feig & Lipton 1993). In synaptosome preparations, glutamate treatment leads to polyribosome formation and translation activation (Weiler & Greenough 1993;Bagni et al 2000).…”