X-Message-Number: 8412 Date: Mon, 21 Jul 1997 09:53:16 -0800 From: "Joseph J. Strout" <> Subject: Re: synapses and LTP In Message #8405, Brian Rowley <> wrote: >As far as electrophysiologists know, LTP (long-term potentiation) is >permanent (i.e., "indefinite"). ...where "indefinate" is defined as "an hour or more". It's a big leap from this to lifetime memories. LTP is poorly understood still; there are apparently effects both pre- and post-synaptically, and teasing apart the roles of the various components has been tricky. But none of the components I've read about are appropriate for very long-term memory storage. A recent review (Science 276:2001-2002) tried to show that the primary effect is mediated by postsynaptic calmodulin-dependent protein kinase II (CaM-KII). CaM-KII is initially activated by calcium, and may maintain its activity by an autophosphorylation feedback loop. Activated CaM-KII, in turn, increases the sensitivy of neurotransmitter receptors at the synapse. While this seems like a reasonable way to adjust the efficacy of a synapse for a few minutes to hours, it's unlikely to underlie memories that last years. First, LTP is only induced by highly artificial stimuli; it may be more of a homeostatic mechanism than a day-to-day learning mechanism. Moreover, it is lost as quickly as it is gained; it lasts hours only when normal stimulation is minimal. Finally, other research has shown that long-term memory is associated with the formation of new synapses, and the retraction of old ones; and that this is necessary for learning (if you block protein synthesis, you can still get LTP, but you can't form new long-term memories). I think the growth and retraction of synapses is a much more likely substrate for long-term memory. LTP most likely serves as either a homeostatic mechanism, or a temporary memory mechanism used as the first stage of a more dramatic physical reorganization. ,------------------------------------------------------------------. | Joseph J. Strout Department of Neuroscience, UCSD | | http://www-acs.ucsd.edu/~jstrout/ | `------------------------------------------------------------------' Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=8412