@misc{oai:ir.soken.ac.jp:00001105,
 author = {遠藤, 利朗 and エンドウ, トシアキ and ENDO, Toshiaki},
 month = {2016-02-17, 2016-02-17},
 note = {To elucidate the fundamental properties of morphologically identified neurons composing local circuits of the superficial layer of the superior colliculus (SC), they investigated the electrophysiological properties and morphological characteristics of neurons in the superficial layer of rat SC, focusing on the following three points:  1) membrane properties and ion conductances, 2) distribution of functionally different subtypes of AMPA-type glutamate receptors and 3) pre- and post-synaptic action of GABA B receptors. 　They performed whole-cell patch clamp recording and intracellular staining with biocytin and/or Ruder yellow in slice preparations of the rat (16 to 23 days old) SC.<br />  According to the firing responses to depolarizing current pulses, the neurons in the superficial layer (n=262) were classified into six classes:  (1) Burst spiking neurons (n=87), (2) Regular spiking neurons (n=131), (3) Late spiking neurons (n=20), (4) Fast spiking neurons (nl), (5) Neurons with rapid spike inactivation (n=11), (6) Neurons with short spike train (n=4).  Majority of recorded neurons were classified either into type (1) or type (2).  In response to hyperpolarizing current pulses, time-dependent inward rectification ("voltage sag", n=120) caused by hyperpolarization-activated current (Ih) and time-independent inward rectification (n=66) caused by inward rectifier potassium channels were observed.  Based on the somatodendritic morphology, the neurons (n=98) were classified into seven groups following previous descriptions:  (a) marginal cells (n=6), (b) narrow field vertical cells (n=15), (c) piriform cells (n=14), (d) horizontal cells (n=18), (e) stellate cells (n=9), (f) wide field multipolar cells (n=8), and (g) wide field vertical cells (n=28).  In general, each groups were heterogeneous with respect to electrophysiological properties among which, although burst spiking and regular spiking neurons consisted the majority.  However, a notable correlation between was observed:  all the type (g) neurons showed marked voltage sag caused by Ih, and voltage clamp analysis revealed that type (g) neurons expressed I with faster activation kinetics and larger current density than the other subclasses.<br />  Among morphologically identified subclasses of neurons, AMPA receptors with inwardly rectifying current-voltage (I-V) relationship were found mainly in horizontal cells, while linear or outwardly rectifying AMPA receptors were found in all the seven cell types.  The inwardly rectifying AMPA receptors were suppressed by 1 mM spermine, while those with linear or outwardly rectifying I-V relationship were not.  The degree of inward rectification was inversely correlated with the reversal potential of current responses of AMPA receptors in Na+-free, isotonic high Ca2+ (20 mM) solution, which is an indicator of Ca2+-permeablity of the receptors.  Thus, Ca2+-permeablity was  higher in inwardly rectifying AMPA receptors.  Furthermore, the AMPA-component of excitatory post-synaptic currents which showed inwardly rectifying I-V relationship and markedly suppressed by 1mM spermine was evoked by electrical stimulation.  These results indicate that Ca2+-permeable AMPA receptors are mainly expressed in horizontal cells and involved in synaptic transmission.<br />  Bath application of baclofen (10-30 μM) elicited hyperpolarization due to an outward current in neurons including narrow field vertical cells, stellate cells, and wide field vertical cells.  The reversal potential of the baclofen-induced current was nearly equal to the equilibrium potential of potassium calculated from Nernst equation, suggesting that GABAB recertors activated the potassium conductance.  Application of baclofen also suppressed both EPSCs and IPSCs evoked by electrical stimulation of adjacent region of recorded cells.  Furthermore, all these effect of baclofen was antagonized by application of specific GABA B receptor antagonist, CGP55845A (0.1-1 μM).  Baclofen had no effect on current responses elicited by bath application of 10 μM kainic acid or 5 μM muscimol under the presence of 0.5 μM tetrodotoxin, suggesting that suppression of synaptic currents  at the presynaptic terminal.  All the above results have clarified the presynaptic an postsynaptic function of GABA B receptors:  actavatuon of GABAergic receptors at t postsynaptac membrane cause hyperpolarization and activation of those at presynaptic terminal suppresses the synaptic transmission at both glutamatergic and GABAergic synapses.   These effects could be observed in a wide variety of cell types in the superfidal layer of the SC.<br />  The findings of ths study add fundamental knowledge about the basis of dynamic properties of visual processing in the SC., application/pdf, 総研大甲第474号},
 title = {Electrophysiological and Morphological Properties of Neurons in the Superficial Layer of the Rat Superior Colliculus},
 year = {}
}