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Notes: [Auszug] The superficial fibular nerve, which normally innervates flexor muscles in the lower leg, was used as the foreign nerve in our experiments. It was dissected, cut peripherally, and transplanted into the proximal surface of the soleus muscle of young rats. Two weeks later the soleus was deprived of ...

Notes: Summary 1. In rabbits, initially anaesthetized by urethane/chloralose and maintained on urethane alone, the perforant path, contacting the apical dendrites of the dentate granule cells by way of boutons en-passage, was activated by paired stimuli. The effect of the first conditioning stimulus was studied by recording the extracellular field response and the extra- and intracellular responses of single granule cells to a second test stimulus. 2. The monosynaptic test EPSP recorded extra- as well as intracellularly was potentiated by a preceding volley in the perforant path. The rate of rise and the amplitude of the extracellular test EPSP increased by as much as 100% at an optimal conditioning-test interval of about 25 msec. The total duration of the potentiation was 200–300 msec. Sometimes the potentiation was followed by a slight subnormal phase. 3. The EPSP potentiation was not due to a larger presynaptic test volley since (1) the size of the presynaptic fibre potential was not effected, and (2) removal of the entorhinal area did not reduce the effect. 4. The potentiation was not due to the recurrent inhibitory hyperpolarization of the postsynaptic membrane because (1) weak conditioning volleys potentiated the EPSPs without discharging the granule cells or producing any inhibition. (2) Conditioning antidromic volleys produced marked inhibition and IPSPs but had no effect on the test perforant path EPSP. 5. Different mechanisms that may be responsible for the EPSP potentiation are discussed. The potentiation is compared with that observed in other types of synapses. Potentiation of EPSPs may be an important mechanism behind the frequency potentiation of mass responses characteristic of the hippocampal formation.

Notes: Summary 1. In rabbits, anaesthetized with urethane/chloralose, stimulation with tungsten microelectrodes was employed to initiate a volley in the perforant path fibres which made en-passage contacts with the apical dendrites of dentate granule cells. The ensuing activation pattern was studied by recording the extracellular field potentials in the dentate area and the extra and intracellular responses of single granule cells. 2. The afferent perforant path volley appeared as a small triphasic potential followed after 0.8 msec by a monosynaptic wave, which was maximally negative in the middle third of the molecular layer, corresponding to the region of the perforant path synapses on the granule cell dendrites. The wave became abruptly positive in the inner third of the molecular layer. After removal of the CA1, reversal occurred also in the outer third of the molecular layer, indicating an active synaptic sink restricted to the middle third of the dendritic region. 3. A perforant path volley, propagating at a speed of about 3.3 m/sec, discharged granule cells lying in a horseshoeshaped segment of the dentate area. The dentate area is thus divided into a series of segments or lamellae by the perforant path input. Laterally, the perforant path fibres run through a bottle neck, deep to the angular bundle, before fanning out to enter the various segments of the dentate area of the dorsal hippocampus. 4. A stimulus applied to the lateral region of the angular bundle activated the perforant path directly as well as indirectly. The indirect activation was presumably mediated by commissural fibres to the entorhinal area from which the perforant path originates. 5. The negativity recorded extracellularly in the synaptic layer had the same onset as, but was phase advanced with respect to the intracellularly recorded EPSP. The monosynaptic extracellular negative wave was therefore interpreted as reflecting the synaptic current generating the intracellular EPSP and is termed the extracellular EPSP. 6. When the perforant path volley was sufficiently large, a compound spike became superimposed on the extracellular EPSP. The spike was maximally negative in the granule cell body layer and positive in the outer dendritic region. Occasionally, multiple single cell discharges could be recorded in the granular layer. These unitary discharges always coincided in time with the compound spike and their number parallelled the size of the compound spike. The latter, therefore, reflects the number of nearly synchronously discharged cells and is termed the granule cell population spike. 7. Typically, the granule cells discharged only once in response to a single perforant path volley. Subsequent discharges were blocked by inhibitory postsynaptic potentials, IPSPs. The postsynaptic excitatory response time varied between 5 msec and 1.4 msec depending on the size of the perforant path volley. A value of about 2 msec was most commonly observed in response to moderate or strong stimuli. 8. The granule cells were discharged by a perforant path volley of increasing size only after a considerable growth of the extracellular EPSP had taken place. Apparently, the discharge requires summation of a large number of relatively small individual EPSPs. This may be a mode of synaptic activation characteristic of pathways with numerous boutons en-passage making contact with spines of profusely branching dendrites.