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Notes: Summary 1.Responses were recorded from 160 ascending tract cells in segments L4 to L6 of the spinal cord in chloralose anaesthetized, spinalized cats. The tract cells were identified by antidromic activation following stimulation of pathways in the lateral and ventral funiculi at the level of the spinal cord transection at the thoracolumbar junction. Axonal conduction velocities ranged from 9 to 114 m/s. 2. A sample of 152 of the neurones examined could be subdivided according to the distribution of their receptive fields into 49 cells activated just from receptors located in skin (“s” cells), 17 neurones excited by receptors in deep tissues (“d” cells), 15 units with a convergent input from receptors in skin and deep tissues (“sd” cells), and 25 neurones with a convergent input from the knee joint and either skin (“sj” cells), deep tissues (“dj” cells) or both (“sdj” cells). No receptive fields could be demonstrated for the remaining 46 neurones. 3. “S” and “sj” cells were found almost exclusively in the dorsal horn, whereas many “d”, “sd”, “sdj” and “dj” units were in the ventral horn. Almost all of the cells that lacked receptive fields were in the ventral horn or intermediate grey. 4. Ninety-one of 158 cells (56%) demonstrated no background activity. Of these, 43 cells (27%) lacked receptive fields. Many of the silent neurones were in the ventral horn, but some were in the dorsal horn. Of 25 cells having knee joint input, 18 (72%) had background activity. 5. All of the neurones that had a receptive field in the knee joint also had a convergent input from receptors in other tissues. In 3 cases, there was a receptive field in the skin over the foot (“sj” cells). For 16 cells, receptive fields included not only the knee joint but also skin and deep tissue (“sdj” cells). Usually, the cutaneous receptive field was near the knee joint, but sometimes it was remote, such as on the foot. The deep receptive fields were chiefly in the muscles of the thigh and/or leg. For 6 “dj” cells, the receptive fields included not only the knee joint but also deep fields like those of “sdj” cells. 6. Cutaneous receptive fields were classified as “low threshold” (cells excited best by innocuous intensities of mechanical stimulation), “wide dynamic range” (cells activated by weak mechanical stimuli, but the best responses were to noxious stimuli) or high threshold (innocuous stimuli had little effect, but noxious mechanical stimuli produced a vigorous discharge). Similarly, stimulation of the knee joint with weak mechanical stimuli could excite some neurones, while others could be activated by weak or strong articular stimuli but were excited best by noxious stimuli, and still other neurones were activated by knee joint stimuli only if the intensity was noxious. 7. In several instances, contralateral receptive fields were noted. These were generally in deep tissue or in the knee joint. 8. It was concluded that many of the responses to articular stimulation of the spinal cord ascending tract cells examined in this study could have been mediated by the fine afferent fibres that supply the knee joint. Although further work will be required to determine which particular ascending tracts transmit nociceptive information concerning the knee joint, it can be proposed that many of the responses demonstrated here were likely to play a role in either joint pain of in triggering responses associated with joint pain.

Notes: Summary 1. Recordings were made from 16 ascending tract cells in the spinal cords of anaesthetized, spinalized cats before and after an acute arthritis was produced by injection of kaolin and carrageenan into the knee joint. 2. The responses tested routinely were to passive flexion of the knee, an innocuous movement. In some cases, responses to other movements were also tested, and changes in background discharge rates were monitored. 3. Control recordings for a period of 1 h or in 3 cases of 3 h indicated that the responses to flexion were reasonably stationary. 4. Four tract cells that initially showed little or no response to flexion of the knee joint developed large responses within 1 to 2 h after inflammation of the joint. 5. Another 9 cells were tested that had responses to flexion of the knee joint prior to inflammation. In 6 cases, inflammation produced enhanced static or transient responses. In 2 cases, the effect of flexion was initially inhibitory or variable, but after inflammation these cells showed large excitatory responses. In the other case, inflammation had no effect. Background discharges were increased by inflammation in 6 of these 9 cells. 6. The effect of inflammation of the knee joint was tested on 3 tract cells that had no clearly defined receptive field in the knee. In 1 case, a response developed to knee flexion after acute inflammation was produced. In the other 2 cases, there were initially responses to knee flexion, but these were unchanged by inflammation. 7. Two of the cells tested had bilateral receptive fields in or around the knee joints. Inflammation of one knee joint enhanced the responses to flexion of the same but not of the contralateral knee in one case but greatly increased the responses to flexion of both knees in the other case. 8. Injections of prostaglandin (PGE2) caused an enhancement of the responses to knee flexion beyond that caused by inflammation in 5 of 7 cases. One cell whose responses to flexion of the knee were unaffected by inflammation showed inhibitory responses to prostaglandin injections into the inflamed knee joint. 9. The effects of inflammation on the responses of ascending tract cells of the spinal cord appear to serve as a useful neural model of the events responsible for the development of arthritic pain.

Notes: Abstract 1. The responses of neurons located in the rostral part of the fastigial nucleus to sinusoidal tilt of the animal were recorded in precollicular decerebrate cats and compared with those elicited by the same stimulation in Purkinje (P) cells located in the vermal cortex of the cerebellar anterior lobe. In particular, by fixing the head and the body of the animal to the tilting table and by rotating the animal around its longitudinal axis, it was possible to elicit a selective labyrinth input without eliciting a neck input. 2. Among the 60 fastigial neurons tested, 43 units responded to sinusoidal tilt at the frequency of 0.026 Hz and at the peak amplitude of displacement of 10°–15°. On the other hand, among 106 P-cells tested for a mossy fiber (MF) response to the labyrinth input, 32 units were affected by the same parameters of stimulation. In both instances the response consisted in a periodic modulation of the discharge frequency, which was related to the position of the animal. Most of the responses of the fastigial units to the labyrinth input were characterized by a peak excitation in phase with side-down tilt of the animal and by inhibition during side-up tilt, whereas most of the MF-responses of the P-cells to the labyrinth input showed just the opposite behavior. 3. The threshold amplitude of tilt responsible for these responses varied in different units from 1° to 3° at the frequency of 0.026 Hz. The sensitivity of the first harmonic of the unit responses to tilt, expressed in percentage change of the average firing rate per degree of displacement, corresponded on the average to 1.73±1.16, S.D., for the fastigal neurons and to 1.61±0.94, S.D., for the P-cells. These values did not change or were only slightly modified as a result of increasing amplitude of stimulation from 1°–3° to 15°–25° at a frequency of 0.026 Hz. Moreover, changes in amplitude of stimulation at the parameters reported above did not greatly modify the phase angle of the first harmonic of the responses relative to the side-down position of the animal. Units located in the medial corticonuclear zone of the cerebellum did not show any change in sensitivity and phase angle of the responses by increasing the frequency of tilt from 0.015 to 0.20 Hz at the fixed amplitude of 10°–15°, thus indicating that these responses depended upon stimulation of macular receptors. In other units, however, these changes in frequency of rotation modified the phase angle of the responses, which became related to velocity rather than to the positional signal, due to stimulation of semicircular canal receptors. 4. The observation that most of the responsive fastigial neurons increased their firing rate, while most of the responding P-cells located in the vermal cortex of the cerebellar anterior lobe decreased their firing rate during side-down rotation of the animal is discussed in relation to the postural changes of the limbs elicited during asymmetric stimulation of macular receptors.

Notes: Summary Electrical stimulation of the sural, superficial peroneal and plantar nerves in anesthetized cats produces a sequence of potentials in the spinal cord lumbosacral enlargement. The distributions of the spinal cord dorsum negative intermediary potential (N1 wave) and of the associated field potential recorded in depth from the spinal gray matter were mapped. The N1 wave produced by the sural nerve was largest at the junction of the S1 and L7 segments, whereas that evoked by the other two nerves was maximum in L6 and L7. The field potentials recorded in depth also showed a differential distribution. The maximum negativity during phase 2, corresponding to the N1 cord dorsum potential, was found to lie laterally in the dorsal horn when the sural nerve was stimulated, but medially when the plantar nerve was activated. The superficial peroneal nerve produced its largest negative field potential in the central region of the dorsal horn. The negative field potentials from the sural and superficial peroneal nerves were not as well separated spatially from each other as they were from the potential evoked by the plantar nerve.