Tag Archives: schinder

Enhanced integrative properties of immature neurons #sfn11

How do the physiological properties of new neurons translate to a behavioral role? Are they just like mature neurons or are they unique? One idea that’s been thrown around is that their plastic period, their critical period, might endow them with an enhanced ability to associate information and contribute to memory formation. While we know that hippocampal neurons are already plastic and very capable of physiologically linking together different stimuli the big hope seems to be that maybe immature neurons are even better at this.

spiking

A related question is how fewer synapses and unique inhibitory connectivity affects their information processing capabilities. The verdict is out on whether new neurons are more or less involved in information processing than their mature counterparts. Currently, the best information we have is from studies looking at activity, measured by immediate early gene expression, in response to behavioral stimulation. The true measure of whether a neuron is involved in information processing / representation is if it spikes, i.e. fires action potentials, in response to a specific stimulus. Since new neurons have fewer synapses it’s very possible that they aren’t able to represent many different types of information, and therefore aren’t capable of associating information during memory formation. On the other hand, new neurons synapses are more plastic, perhaps making them better able to associate information even if they have fewer synapses. Continue reading Enhanced integrative properties of immature neurons #sfn11

Are new neurons really more excitable? (yes)

ResearchBlogging.orgSome facts on neuronal excitability:

  1. Excitable: the ability to fire action potentials.
  2. More excitable: fires action potentials, but more.
  3. More LTP: not the same as more excitable.
  4. Less inhibition: also not the same as more excitable, though the two may go hand in hand.
  5. The Scholarpedia page on neuronal excitability, which was last modified on 13 August 2009, has been accessed 49,025 times, and contains no information (peer review is slow).

One of the claims that is often made is that adult-born neurons are more plastic and more excitable than older neurons.  This despite there being little evidence (until recently) that new neurons indeed are more excitable. But, hey, “excitable” sounds great alongside “plastic”. The Schmidt-Hieber paper did show that new neurons are more excitable, though it wasn’t their main focus and it is only occasionally referenced as evidence for greater excitability.

My misunderstanding that there are no thorough investigations of new neuron excitability was brought to an end recently when I was fortunate to have an infant-free moment (In which I was able to read two papers in the same evening, plus an entire New Yorker article over breakfast. Amazing.) One of the papers was Reliable Activation of Immature Neurons in the Adult Hippocampus by Mongiat et al. from Alejandro Schinder’s lab, which I really should have read long ago. Continue reading Are new neurons really more excitable? (yes)

Everything you always wanted to know about neurogenesis timecourses (but were afraid to ask)

Most studies of adult neurogenesis are concerned with neuronal age. Or at least they should be. This is because new neurons develop from a stage where they have no excitatory synapses to one where they have many. If we assume the traditional view that information is stored at excitatory synaptic connections, then young neurons are initially useless and only become physiologically and behaviorally meaningful when they have matured to a point where they can relay and process information. It is therefore critical that the developmental timecourse of new neurons be mapped out, so we know when new neurons become functionally relevant, or whether they might even have different functions at different ages.

Below are what I hope to be comprehensive visual collages of all published timecourse experiments, where a certain property of new neurons is examined at multiple (≥ 3) different ages. They are grouped by studies of: 1) cell survival, 2) marker expression, 3) functionality, and 4) miscellaneous studies that do not quite fit into the first 3 categories. I’ve ordered the data roughly chronologically and have included the first author’s name and publication year so you can read deeper, if needed. Indeed, if you know these studies already, a brief look at the graphs will bring back the take home message. However, since the data is stripped of text, if the studies are unfamiliar, you’ll have to go to the original source to figure out what the heck they mean (use Pubmed to at least obtain abstracts for the original studies if I didn’t provide a direct link).

Personally, I like timecourse studies for the same reason I like to have all my music albums or books visible at the same time: at a single glance they provide a lot of information – each individual stage of maturation can be interpreted within a bigger picture. The result of these many hours of work will either be a) that the purpose of adult neurogenesis will become immediately clear, or b) that we’ll all have some fancy collages to pin on our bulletin boards and look intelligent.

The survival timecourse

addition of new neurons

New neurons are born and then many die. The survival timecourse answers the questions: How many new neurons are born? Where are they born and where do they end up, anatomically? How many of them survive and can their survival be altered? Survival timecourses are typically performed by injecting animals with a mitotic marker that will label new neurons as they’re being born, e.g. ³H-thymidine (old school), BrdU (tried and true – example), or a GFP-expressing retrovirus (new school). At a later date one can then detect these birthdated new neurons and count them, see where they’re located etc.

Continue reading Everything you always wanted to know about neurogenesis timecourses (but were afraid to ask)