Figure 6.

Location and identification of RE neurons. (A–D) Location of RE neurons recorded during locomotion. Estimated locations of neurons are combined from two cats and are shown by various symbols on frontal sections of thalamus of one of them: ■, Purple squares show neurons with somatosensory receptive fields on the shoulder: responding to passive movements in the shoulder joint and/or palpation of muscles on the back or neck; ♦, Yellow diamonds show cells that were activated by movements in the elbow; ▲, Red triangles represent neurons with receptive fields on the wrist or paw. In (A), an arrowhead is pointing to a reference electrolytic lesion and an arrow indicates the site of injection of red fluorescent beads. (A) close-up to the injection site is shown in the insert. Abbreviations: AM, nucleus anterio-medialis; AV, nucleus anterio-ventralis thalami; CI, capsula interna; DH, dorsal hypothalamus; EPN, nucleus entopeduncularis; MV, nucleus medio-ventralis; NC, nucleus caudatus; RE, nucleus reticularis thalami; VA, nucleus ventralis anterior. Frontal 50 μm thick sections, cresyl violet stain. (E–H) Identification of RE neurons by characteristic profile of their bursts during sleep. (E) Cat sleeping with its head restrained. (F,G) An example of activity of a RE neuron while cat is awake and asleep. At the beginning of the record desynchronized activity in EEG indicates that the cat was awake, and the neuron was discharging fairly regularly. The arrow points to the beginning of “spindle waves” in EEG, which are a sign of beginning of slow wave sleep. Shortly thereafter very high frequency irregular bursts separated by long periods of inactivity replaced the regular discharge of the neuron. (H) Close-up on a burst. The first interspike interval in this burst was longer than the second one, and the second interval was longer that the third. Several following interspike intervals were of an approximately similar duration, while the last ones were progressively longer. The lower trace shows change of discharge frequency within the burst. Such a burst with ramping up and then winding down firing rate identifies this neuron as belonging to the RE. (I) Identification of the motor compartment of the RE by responses of neurons to electrical stimulation of the VL (upper trace) and MC (lower trace). In response to either stimulation the cell generates a short latency burst followed by a period of silence and then by another burst. (J) Locomotion-related activity of a representative neuron with shoulder-related receptive field. The activity of this neuron is modulated to strides but does not contain any “sleep-type” busts. (K) Accelerating-decelerating frequency “sleep-type” bursting during locomotion in a wrist/paw-related neuron. A burst is shown in the insert at a fast time scale. Such bursts often appeared at the beginning of the locomotion-related activation of this neuron. (L–O) Thalamic projections to the area of recording in the RE. Neurons in the VL and VL/VPL border zone in one of the cats where red fluorescent beads were injected in the rostro-lateral part of the explored RE area, retrogradely labeled with red fluorescent beads. Neurons are shown on photomicrographs of frontal sections of the left thalamus ipsilateral to the injection site. Each circle represents one labeled neuron. Abbreviations: CL, nucleus centralis lateralis; LA, nucleus lateralis anterior; LG, lateral geniculate nucleus; LP, nucleus lateralis posterior; OT, optic tract; PC, pedunculus cerebri; VL, nucleus ventralis lateralis; VM, nucleus medialis; VPL, nucleus ventralis postero-lateralis; VPM, nucleus ventralis postero-medialis; other abbreviations are as in Figure 5 (Adapted with modifications from Marlinski et al., 2012b).