Fast-spiking interneurons and the critical period

How do children learn to play instruments and speak languages so much easier than adults, and why does brain damage result in worse outcomes in the mature brain vs. the young brain?  These questions are central to the study of how “critical periods” are regulated in the brain.


Electron micrograph from a single 70 nm cross-section through a fast-spiking parvalbumin-containing (gold labeling = white dots) presynaptic terminal forming a synapse (red dots) with a pyramidal soma. Original colors are inverted, contours have been raised and membranous structures are highlighted in aqua for ease of visualization. Presynaptic vesicles (colored ovals) within perisomatic fast spiking terminals mostly cluster within ∼200 nm of the synapse, with a few close enough (≤2 nm) to be deemed docked.

Critical periods in brain development define temporal windows when neuronal physiology and anatomy are most sensitive to changes in sensory input or experience (e.g. sound, touch, light, etc.).  The maturation of inhibitory cells that release the neurotransmitter GABA, especially a subset called fast-spiking (FS) interneurons, is thought to gate this period of neuronal ‘plasticity’ in the mammalian primary visual cortex.  However, it has remained unclear what aspects of FS cell development are important for permitting this period of neuronal malleability in the visual cortex. A new paper in Journal of Neuroscience from the Turrigiano lab addresses the question.

To explore how FS cell development might be linked to critical period plasticity, Brandeis postdoc Marc Nahmani and Professor Gina Turrigiano employed a well-established assay for cortical plasticity in visual cortex called monocular deprivation (MD), and measured FS cell connections using confocal and electron microscopy, as well as optogenetic stimulation of the FS cell population (i.e. shining light onto FS cells possessing light-gated channels to make them fire action potentials).

Following up on previous work from the Turrigiano lab (Maffei et al., 2006), they found that MD induces a coordinated increase in FS interneuron to pyramidal cell (the major excitatory output cells of the cortex) pre- and postsynaptic strength.  These changes occur if MD is performed during, but not before the critical period in visual cortex, suggesting they may play a role in gating this period of heightened neuronal plasticity.  Future studies are aimed at determining the timeline for these changes across the extent of the critical period in visual cortex.

see: Nahmani M, Turrigiano GG (2014) Deprivation-Induced Strengthening of Presynaptic and Postsynaptic Inhibitory Transmission in Layer 4 of Visual Cortex during the Critical Period. Journal of Neuroscience 34:2571-2582.

Brandeis Science online tidbits

Another way that flies sense temperature

If you remember your (bio-)physical chemistry, you’ll remember that most proteins are temperature sensitive. But which ones acts as the sensors that drive behavior in higher organisms? The Garrity Lab at Brandeis has been working on thermosensation in Drosophila, and previous work has implicated the channel protein TRPA1 as a key mediator of temperature preference and thermotaxis,  In a new paper in Nature, members of the Garrity lab working in collaboration with the Griffith and Theobald have have identified another protein, GR28B(D), a member of the family of gustatory receptor proteins, as another behaviorally important temperature sensor, involved in rapid avoidance of high temperatures. Authors on the paper include postdocs Lina Ni (lead author) and Peter Bronk, grad students April Lowell (Mol. Cell Biology) and Vincent Panzano (PhD ’13, Neuroscience), undergraduate Juliette Flam ’12, and technician Elaine Chang ’08.

  • Ni L, Bronk P, Chang EC, Lowell AM, Flam JO, Panzano VC, Theobald DL, Griffith LC, Garrity PA. A gustatory receptor paralogue controls rapid warmth avoidance in Drosophila. Nature. 2013.
  • story at BrandeisNOW


Mugdha Deshpande named Blazeman Postdoctoral Fellow

Assistant Professor of Biology Avital Rodal has received a grant from the Blazeman Foundation to study the traffic of growth signals in neurons in the animal models of ALS (Amyotrophic Lateral Sclerosis).  ALS, commonly known as ‘Lou Gehrig’s disease’, is a neurodegenerative disease that causes the loss of motor neurons. The Blazeman Foundation is a non-profit organization working to increase the awareness about this terminal disease and to support research towards finding treatments. Funding to the Rodal lab has enabled creation of the Blazeman Foundation Postdoctoral Fellowship for ALS Research, awarded to Mugdha Deshpande, Ph.D., who will use live imaging to examine and manipulate membrane traffic in fruit fly models of ALS, and who will also work with Dr. Suzanne Paradis to translate her findings to mammalian ALS models.

You can read more at BrandeisNOW.

Marder lab researchers win best paper contest

Alex Williams and Timothy O’Leary from the Marder Lab have won first place in the 2012  Brain Corporation Prize Competition in Computational Neuroscience  for their Scholarpedia article Homeostatic Regulation of Neuronal Excitability.  Williams, a Bowdoin College graduate currently working as post-baccalaureate research technician at Brandeis, and O’Leary, a postdoctoral fellow, won the worldwide competition to write the most popular review in the area of computational neuroscience, and gained a $5,000 prize, a feat that required not only superb writing but also mobilizing the audience to vote for paper. The award ceremony is today at the Computational Neuroscience (CNS’13) meeting in Paris.

Check out the winning entry online.

How does the brain decide whether you like what you eat?

When we encounter a taste, we appreciate both its chemosensory properties and its palatability—the degree to which the taste is pleasurable or aversive. Recent work suggests that the processing of this complex taste experience may involve coordination between multiple brain areas. Dissecting these interactions help understand the organization and working of the taste system.

F4.largeThe lateral hypothalamus (LH) is a region of the brain important for feeding. In a rodent, damage the LH, and the rodent may starve itself to death; stimulate it, and you get a curious mix of voracious eating and expressions of disgust over what is being eaten. Such data suggest that LH plays a complex game of balancing escape and avoidance, palatability and aversion, during the evaluation of a taste stimulus. Little is known, however, about how neurons in LH actually respond to tastes of different valences.

Brandeis postdocs Jennifer Li and Takashi Yoshida. undergraduate Kevin Monk ’13, and Associate Professor of Psychology Don Katz have recently published a study of neuronal reponses in LH in the Journal of Neuroscience. They have shown that taste-responsive neurons in LH break neatly down into two groups–one that responds preferentially to palatable tastes and one to aversive tastes. Virtually every taste neuron in LH could be identified as a palatable- or aversive-preferring neuron. In addition, even without considering the specific tastes to which a particular neuron responded, these two groups of neurons could be differentiated according to their baseline firing rate, shape of response, and tuning width. While these neurons were spatially intermingled, several pieces of data (functional connectivity analysis, relationship to responses in amygdala and cortex) suggest that they are parts of distinct neural circuits. These results offer insights into the multiple feeding-related processes that LH manages, and how the hypothalamus’ role in these processes might be related to its connection to other parts of the taste system.

Li JX, Yoshida T, Monk KJ, Katz DB. Lateral Hypothalamus Contains Two Types of Palatability-Related Taste Responses with Distinct Dynamics. J Neurosci. 2013;33(22):9462-73.

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