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In part branching off a discussion here, but also a discussion I've always been interested in having. I also want to take some time to answer the question in that thread:
axo-axonic gap junctions in the hippocampus are thought to play a role in generating ultra-fast oscillations that have a unique "spikelet" shape that participates in some higher level functions [1]:
Axo-axonic gap junctions are also capable of antidromic action potentials [2] which can give alternate routes of excitation and inhibition (a gap junction, of course, acts somewhat like an inhibitor with respect to the neuron at the higher potential).
and address this comment:
Firstly, I'd just like to point at that it's true that ephaptic coupling, but electrical coupling through gap junctions is not considered ephaptic coupling [3]. Ephaptic coupling is coupling through environment, such as local electric fields and local ion exchange with extracellular space, not direct gap junction coupling.
The well known gap junctions role is synchronization [4], but they also pass molecular signaling molecules, leading one author to refer to them as the "rosetta stones" of biology (because they can integrate electrophysiological and metabolic communication) [5]. Electrical synapses are also found extensively coupling GABAergic interneurons in the cortex, and are thought to participate in coincidence detection across inhibitory signals [6]. They also appear to functionally segregate portions of network [7]. Experiments in C.elegan show that interfering with different kinds of gap junctions can lead to numerous different functional deficiencies (from constipation to chemotaxis to death) [8]. And of course, the nervous system is dominated by gap junctions in early development [9].
The chief blockers and openers of gap junctions (because gap junctions can be open, rectifying, or closed) are carbenoxolone and trimethylamine.
[1] http://www.sciencedirect.com/science/article/pii/S0361923003002302
[2] http://www.sciencedirect.com/science/article/pii/S0306452298007556
[3] http://www.nature.com/neuro/journal/v14/n2/abs/nn.2727.html
[4] http://www.sciencedirect.com/science/article/pii/S0166223699014976
[5] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3058197/
[6] http://www.nature.com/nrn/journal/v2/n6/abs/nrn0601_425a.html
[7] http://www.sciencedirect.com/science/article/pii/S0166223605000998
[8] http://www.ncbi.nlm.nih.gov/pubmed/24575048
[9] http://www.jneurosci.org/content/3/4/773.short
atty said:What sort of phenomena or behaviour do axo-axonic gap junctions produce?
axo-axonic gap junctions in the hippocampus are thought to play a role in generating ultra-fast oscillations that have a unique "spikelet" shape that participates in some higher level functions [1]:
Recent studies both in vivo and in vitro have revealed rhythmic, synchronous population activity, such as gamma frequency (30–80 Hz) oscillations 34., 87., 98. and 121. and ultrafast sharp-wave “ripples” (>80–200 Hz) 31. and 124., in mammalian brains. These oscillations are thought to play an important role in a variety of cognitive processes, including memory formation, sensory perception, and other higher functions 44. and 87.. Evidence for electrical signaling between homogeneous populations of neurons involved in generating these rhythms is strong. Coupling was initially demonstrated between principal (pyramidal) cells 61., 62. and 101. but also, more recently, between interneurons 5., 36., 39., 40., 50., 64., 65., 99., 100. and 117.. A number of reviews have detailed the properties of gap junctions 8., 9., 28. and 29., their role in interneurons 37. and 102., and network activity, especially during development 25. and 79., and epilepsy 20., 32., 51., 72., 107. and 112.. The aim of this review is to discuss the importance of electrical signaling in synchronizing network activity. In particular, we will focus on two types of rhythmic activity observed in the hippocampus both in vivo and in vitro—gamma frequency oscillations and ultrafast oscillations.
Axo-axonic gap junctions are also capable of antidromic action potentials [2] which can give alternate routes of excitation and inhibition (a gap junction, of course, acts somewhat like an inhibitor with respect to the neuron at the higher potential).
and address this comment:
DiracPool said:Ephaptic coupling including electrical gap junctions are prevalent in the brain but are more of an anomaly than a selected design feature, as far as we can tell. There doesn't seem to be any conserved pattern of any type of ephaptic coupling across brain taxa that would suggest it has any specific role in sensory-motor information processing, at least.
Firstly, I'd just like to point at that it's true that ephaptic coupling, but electrical coupling through gap junctions is not considered ephaptic coupling [3]. Ephaptic coupling is coupling through environment, such as local electric fields and local ion exchange with extracellular space, not direct gap junction coupling.
The well known gap junctions role is synchronization [4], but they also pass molecular signaling molecules, leading one author to refer to them as the "rosetta stones" of biology (because they can integrate electrophysiological and metabolic communication) [5]. Electrical synapses are also found extensively coupling GABAergic interneurons in the cortex, and are thought to participate in coincidence detection across inhibitory signals [6]. They also appear to functionally segregate portions of network [7]. Experiments in C.elegan show that interfering with different kinds of gap junctions can lead to numerous different functional deficiencies (from constipation to chemotaxis to death) [8]. And of course, the nervous system is dominated by gap junctions in early development [9].
The chief blockers and openers of gap junctions (because gap junctions can be open, rectifying, or closed) are carbenoxolone and trimethylamine.
[1] http://www.sciencedirect.com/science/article/pii/S0361923003002302
[2] http://www.sciencedirect.com/science/article/pii/S0306452298007556
[3] http://www.nature.com/neuro/journal/v14/n2/abs/nn.2727.html
[4] http://www.sciencedirect.com/science/article/pii/S0166223699014976
[5] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3058197/
[6] http://www.nature.com/nrn/journal/v2/n6/abs/nrn0601_425a.html
[7] http://www.sciencedirect.com/science/article/pii/S0166223605000998
[8] http://www.ncbi.nlm.nih.gov/pubmed/24575048
[9] http://www.jneurosci.org/content/3/4/773.short