Intracellular records of the effects of primary afferent input in lumbar spinoreticular tract neurons in the cat.
1. The afferent-evoked synaptic input to lumbar spinal cord (L5-S1) neurons that were activated antidromically from the medial pontomedullary reticular formation (nucleus reticularis gigantocelluaris and vicinity) was investigated with the use of intracellular recordings in pentobarbital sodium-anesthetized cats. 2. Spinoreticular tract (SRT) neurons (n = 33) were categorized into three types ("deep-inhibited," "deep-complex," and "intermediate") on the basis of their locations and of their responses to natural and electrical stimulation. 3. The deep-inhibited-type neurons, located in the medial part of the deeper laminae (approximately VI-VIII), comprised a large component of the sample (20/33). They had no demonstrable excitatory receptive field (RF). However, electrical stimulation of low-threshold cutaneous afferents of hindlimb nerves evoked inhibitory postsynaptic potentials (IPSPs) via an oligosynaptic linkage. High-threshold cutaneous and muscle afferents also evoked IPSPs. 4. In the deep-complex-type neurons (8/33), electrical stimulation of low-threshold cutaneous afferents evoked complex IPSP-excitatory postsynaptic potential (EPSP) sequences. With intense stimuli, long-latency C-fiber-like EPSPs were evoked. Two of these eight neurons were characterized as wide-dynamic-range (WDR) neurons with large, excitatory and inhibitory cutaneous RFs. 5. Intermediate-type neurons (5/33) were concentrated in the lateral spinal gray and relatively superficially (approximately lamina V). These neurons had convergent low- and high-threshold cutaneous inputs (WDR neurons). Electrical stimulation of low-threshold cutaneous afferent fibers from within the excitatory RF evoked mono- or disynaptic EPSPs followed by IPSPs. High-threshold muscle and cutaneous afferents also evoked EPSPs. 6. These results show that SRT neurons have a variety of response characteristics resulting from various degrees of spatial and temporal summation of primary afferent input. Neurons with widespread inhibitory responses but no excitatory drive from the periphery comprise a surprisingly large component of the SRT: the function of these cells is unknown. It is apparent that the spinoreticular projection has considerable functional heterogeneity.
Sahara
Y
Y
Neurobiology and Anesthesiology Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
Xie
Y K
YK
Bennett
G J
GJ
D000818:Animals; D001933:Brain Stem / Q000166:cytology / Q000502:physiology; D002415:Cats; D004558:Electric Stimulation; D004566:Electrodes; D005071:Evoked Potentials / Q000502:physiology; D006614:Hindlimb / Q000294:innervation / Q000502:physiology; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D012154:Reticular Formation / Q000033:anatomy & histology / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D013569:Synapses / Q000502:physiology