1980 Volume 92 Issue 1-2 Pages 219-235
An electrode was stereotaxically implanted in the unilateral dentate nucleus (DN), the contralateral ventrolateral nucleus of the thalamus (VL) and on the surface of the contralateral anterior sigmoid gyrus (ASG) in thirty-five cats.
The evoked responses from the contralateral VL and ASG following DN stimulation were studied using an averaging computor technique. Electrical stimulation of DN was commenced in an unanesthetised state 4 to 5 days after the implantation. Square pulse current, 0.2 msec in duration was applied at a frequency of 1 Hz. Modification of the evoked responses was studied following parenteral administration of various centrally acting agents.
The results were as follows.
1) Single stimulation of the DN demonstrated evoked responses in the contralateral VL with N1 (first negative), P1 (first positive), N2 (second negative), followed by P2 (second positive), and N3 (third negative). Peak latencies of these waves were estimated to be 0.8±0.1 msec in N1, 1.1±0.2 msec in P1, 1.5±0.3 msec in N2, 2.4±0.4 msec in P2, and 5.3±1.2 msec in N3.
N1 and N2 corresponded to presynaptic tract response and postsynaptic relayed response respectively. From the latencies of N1 and the distance between VL and DN (21 mm), the conduction velocity in the dentato-thalamic pathway was roughly calculated as 23-30 m/sec.
2) The evoked responses on the contralateral ASG following a single stimulation of the DN demonstrated a wave form composed of P1, N1, P2, and N2. Peak latencies of these waves were estimated to be 2.1±0.4 msec in P1, 3.3±0.5 msec in N1, 5.8±0.7 msec in P2, 13.2±1.9 msec in N2. P2 and N2 is corresponding to Creutzfeldt's primary EPSP and secondary EPSP respectively.
3) The effects of various centrally acting agents on the above mentioned evoked responses were observed (See table 3).
1 L-5HTP markedly decreased the amplitudes of both P2 and N2 of ASG responses. PCPA caused no paticular changes.
2 AOAA also caused effects upon ASG responses similar to L-5HTP. A subconvulsive dose of picrotoxin caused no particular changes.
3 Atropine decreased the amplitudes of both P2 and N2 in ASG. Physostigmine caused no particular changes.
4 L-Dopa and ET495 tended to stabilize ASG responses especially when it was in the suppressed state. Reserpine and haloperidol caused no particular changes.
These data suggest that 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (GABA), acetylcholine (ACh), and dopamine (DA) do not play a primary role in the dentato-thalamocortical pathway but work indirectly through other neuronal pathways. This method using evoked responses seems to be useful to know the site and the time course of drug action in relation to the function of a pathway.
