Figure 1.
Schematic representation of the experimental setup and time-course.
A: Experimental setup. A pair of bipolar stimulating electrodes was placed in the forelimb region of the supplementary motor area (SMA). A glass-coated Elgiloy-alloy microelectrode was inserted obliquely into the internal segment of the globus pallidus (GPi) for extracellular single-unit recording. The NeuRet-IL-2Rα-GFP vector was injected into the SMA-recipient territory of the subthalamic nucleus (STN) according to the mapping of cortically evoked responses therein. Four-to-six weeks later, immunotoxin (IT) was injected into the SMA forelimb region. Cd, caudate nucleus; GPe, external segment of the globus pallidus; Put, putamen. B: Experimental time-course. Neuronal recordings from the GPi in a control condition were performed before the IT injections into the SMA. Later than two weeks (wks) after the IT injections, GPi recordings were resumed.
Figure 2.
Effects on GPi neuron responses of selective elimination of the cortico-STN projection.
A: Typical examples of peri-stimulus time histograms (PSTHs; bin width of 1 ms, summed for 100 stimulus trials) in monkey G before (1) and after (2) IT injections into the SMA. Electrical stimulation in the SMA was given at time = 0 (arrows). In each PSTH, the mean firing rate and statistical levels of P<0.05 (one-tailed t-test) calculated from the firing rate during 100 ms preceding the onset of SMA stimulation are indicated by the solid white line (mean), broken black line (upper limit of P<0.05), and broken white line (lower limit of P<0.05), respectively. The excitatory and inhibitory responses are represented in red or cyan color, respectively. The amplitude of each response was defined as the number of spikes in the colored area. B: Typical examples of spontaneous activities denoted by slow traces of digitized spikes and autocorrelograms (bin width of 0.5 ms) in monkey G before (1) and after (2) IT injections into the SMA.
Figure 3.
Population histograms of GPi neuron responses.
Data obtained before (blue lines) and after (red lines) IT injections into the SMA in monkey M (A; before IT, n = 4; after IT, n = 18), monkey G (B; before IT, n = 9; after IT, n = 13), and monkey U (C; before IT, n = 9; after IT, n = 10). The light shaded colors represent ±1 SD. A,B: The early excitation was diminished without either the inhibition or the late excitation affected. C: Control case without vector injections into the STN. No apparent changes were observed after the IT injections into the SMA.
Table 1.
Amplitude of cortically-induced triphasic responses (early excitation, inhibition, and late excitation) of GPi neurons before and after IT injections into the SMA.
Table 2.
Firing patterns of GPi neurons before and after IT injections into the SMA.
Figure 4.
Retrograde and anterograde neural tracings.
A: Retrograde neuronal labeling in the orofacial and forelimb regions of the SMA after Fluoro-ruby (FR) injection into the STN in monkey M. Lower panels a,b denote higher-power magnifications of the rectangular areas in upper panels. Scale bars, 500 µm for upper panels and 200 µm for lower panels. B: Distribution of FR-positive neurons in the orofacial (OF), forelimb (FL), and hindlimb (HL) regions of the SMA. Cell counts were carried out in 17 equidistant frontal sections taken from Monkey M. Note that FR-positive neurons are so few in the FL region where IT injections were made (at two rostrocaudally distinct levels pointed to by arrows), as compared to those in the OF and HL regions. Numerals on the abscissa represent the distance from rostrocaudal zero on the stereotaxic frame (equivalent to the interaural line). C: NeuN immunostaining of the orofacial and forelimb regions of the SMA. Note that the IT injections cause no marked neurotoxic insult. Scale bars, 500 µm. D: Anterograde terminal labeling in the STN after BDA injections into the SMA forelimb region. Left: monkey U without vector injections into the STN. Right: monkey G with vector injections into the STN. Note that BDA-labeled axon terminals are much less densely observed in the STN after the IT injections into the SMA combined with the vector (IL-2Rα) injections into the STN. Scale bars, 50 µm. E: Terminal labeling in the putamen in monkeys U (left) and G (right). Note that virtually no difference in the density of labeled terminals is found between the two cases. ic, internal capsule. Scale bars, 50 µm.