Figure 3.

Identification and spontaneous discharge activity of corticostriatal neurons during slow waves. A, Striatonigral MSNs are preferentially innervated by cortical neurons that project into telencephalon (IT-type), whereas striatopallidal MSNs receive greater input from those that send their main axon into pyramidal tract (PT-type) (Lei et al., 2004). Because IT-type neurons project into both striatum whereas PT-type neurons only innervate the ipsilateral striatum, the antidromic stimulation of both striatum can be used to discriminate between IT-type and PT-type neurons. B, Example of an IT-type neuron exhibiting antidromic responses to stimulation of both striatum. Striatal stimulation was triggered by spontaneous spikes with a time interval of 30 ms (left) or 3 ms (right). Recordings show the superimposition of 10 successive responses to striatal stimulation in both conditions. Notice the fixed latency of the antidromic spikes (left) and the collision of the spontaneous spike with the antidromic one at short intervals (right). Only neurons that fulfilled the three criteria (see Materials and Methods) of a double antidromic response from both striatum were considered to be of the IT-type. Neurons that only exhibited an antidromic response to ipsilateral stimulation were presumed to be of the PT-type. Cortical neurons that did not show any antidromic response were discarded. C, Simultaneous recording of the cortical field potential and of the discharge activity of the IT-type neuron identified in B, recorded in a 6-OHDA-lesioned rat. During SW⁺ state, all corticostriatal neurons discharged during the maximum of the SWs. D, Temporal relationship between discharge activity and slow waves. The discharge activity (75 spikes) was recorded simultaneously with the field potential during a continuous period of SW⁺ state (388 s). Sections of field potential recordings centered on every spike were averaged together. On average, this IT-type neuron recorded in a 6-OHDA-lesioned rat discharged after the maximum of the slow waves. E, Spontaneous discharge rate of corticostriatal neurons. Bar histograms indicate mean ± SEM (unpaired t test, *p = 0.0001, **p = 0.0002; other differences p ≥ 0.14). The number of neurons studied is indicated inside bars. These neurons were recorded from nine sham-lesioned rats (filled bars) and from eight 6-OHDA-lesioned rats (open bars). F, The discharge activity of two IT-type neurons was analyzed with ISI histograms (2 ms bin). G, Power spectrum built from field potentials recorded in the cortex of one sham-lesioned rat and of one 6-OHDA-lesioned rat. Field potential was recorded during periods of continuous SW⁺ state lasting for 2–10 min. Dopaminergic depletion strongly depressed the mean discharge rate of IT-type neurons.