Dendritic spike

As can be seen from Fig. 30-32, neurons send "trains" of spikes down their axons. These form synapses with dendrites, usually on dendritic spikes, of a postsynaptic cell.593,1007-1009 However, each such cell typically receives input from thousands of other neurons. At any moment most of these are probably "silent," but others are sending trains of impulses. Among the important questions are "How does the postsynaptic neuron know whether to fire or not " and "What kinds of information, if any, are encoded in the trains of impulses both in the presynaptic inputs and in the output of the postsynaptic neuron "10101011 Part of the answer to the first question is probably that firing occurs if two or more input impulses arrive synchronously,10101012-1014 and if there are not too many inhibitory impulses that damp the response. In the hippocampus a network of neurons electrically coupled via gap junctions may be synchronized to the theta and gamma brain rhythms by high-frequency (150-200 Hz) oscillations.988 See also Fig. 30-15. 

Baer, S.M., Rinzel, 1. Propagation of dendritic spikes mediated by excitable spines a continuum theory. J. NeurophysioL 65(4), 874—890 (1991). http //jn.physiology.org/cgi/ content/abstract/65/4/874... 

Fig. 18. Intradendritic recordings from a CAl pyramidal cell. (A) Postsynaptic activities evoked by striatum radiatum stimulation. Control dendritic spike (in trace 1) was recorded in penetration 350 p,m away from the cell-body layer. In traces 2-4, hyperpolarizing currents applied during orthodromic stimulation blocked the spike in steps and uncovered an excitatory postsynaptic potential (trace 4). (B) Spontaneous (trace 1) and directly evoked burst (trace 2) in the same dendrite as in (A). TTX-resistant activity of this dendrite is shown in trace 3. Whereas short-duration (20 msec) depolarizing pulses could evoke depolarizations that triggered bursts (trace 2), excitatory postsynaptic potential of comparable duration that produced even larger depolarizations only evoked a spike [cf. trace 1 in (A) and trace 2 in (B)]. Membrane potential 60 mV. Lower trace is the current monitor. (From Wong et ai, 1979.)...

LlinAs, R., and Hess, R., 1976, Tetrodotoxin-resistant dendritic spikes in avian purkinje cells, Proc. Natl. Acad. Sci. USA 73 2520-2523. 

LlinAs, R., and Nicholson, C., 1969, Electrophysiological analysis of alligator cerebellar cortex a study on dendritic spikes, in Neurobiology of Cerebellar Evolution and Development (R. LlinAs, ed.), pp. 431-465, Chicago American Medical Assoc. 

The pits exhibit dendrite crystalline phases embedded in glassy matrix. Dendrite usually appears when the temperature gradient is prevented and supercooling is large. Dendrite spikes also remain isolated because the latent heat released during spike formation raises the temperature in the immediate vicinity retarding growth of similar projections. After 100 and 750 h of heat treatment for the BL/Y8Z diffusion couple at 850°C, the closed pits decreased to an area of 25,434 and 314 pm. ... 

First, their opening during somato-dendritic action potentials provides the source of the increased intracellular [Ca +] required to open Ca +-activated K+ channels — BK channels, to accelerate spike repolarisation, and SK channels, to induce spike-train adaptation and limit repetitive firing. The BK channels are activated (primarily) following entry of Ca + through L-type channels the source of Ca + for SK channel activation varies with different neurons, and may be either through L-type or N-type channels. 

The dendrites of neurons adjacent to those which degenerate also show extensive growth and sprouting which could facilitate abnormal and disorganised synaptic transmission and cause hyperactivity. It is also known that the dendrites of cells around an alumina focus in monkeys, as well as in human epileptic brain, lose their spinous processes, which might contribute to the paroxysmal discharge by facilitating the spread of depolarisation to the neuron soma. Certainly an increase in the number of Na+ channels on the dendrites of spinal motoneurons, which would facilitate the occurrence of reactive dendritic Na+ spikes, has been seen after axotomy. 

Stanton, P. K. Sarvey, J. M. (1987). Norepinephrine regulates long-term potentiation of both the population spike and dendritic EPSP in hippocampal dentate gyrus. Brain Res. Bull. 18, 11519. 

T-type calcium channels play critical roles in shaping the electrical and plastic properties of neurons and are also implicated in hormone secretion, differentiation and muscle development (Huguenard, 1996 Perez-Reyes, 2003). In thalamic reticular and relay neurons, T-type channels contribute to rhythmic rebound burst firing and spindle waves associated with slow-wave sleep. T-type channels also play crucial roles in dendritic integration and calcium-mediated spiking in hippocampal pyramidal cells, and in synaptic release at olfactory dendrodendritic... 

P6rez-Garci E, Gassmann M, BettlerB, Larkum ME (2006) The GABABib isoform mediates long-lasting inhibition of dendritic Ca2+ spikes in layer 5 somatosensory pyramidal neurons. Neuron 50 603-16... 

Noebels I was struck by the resemblance of the linear jump shift transition to a plateau that you saw, and the data that Hodgkin, Stein and others have described for axons (Jack et al 1975). Can intense or persistent depolarization cause not only a spread of the initiation site to properties of proximal dendrites, but also beyond the axon to possibly even the first node This would result in spike initiation at the first node that could backfire and contribute in some way to the f—I parameters that you see. 

Waxman Some years ago, Mahlon Kriebel, Mike Bennett and I studied oculomotor neurons in fish. They have spike trigger zones in the cell body and in the dendrites, but when they fire at high frequency, you can see the spike initiation zone migrating from one site to the other. It is not a fixed patch of membrane as you are implying. 

Golding NL, Jung HY, Mickus T, Spruston N 1999 Dendritic calcium spike initiation and repolarization are controlled by distinct potassium channel subtypes in CAI pyramidal neurons. J Neurosci 19 8789-8798... 

---