Cortical neuronal ensembles driven by dorsal horn spinal neurones with spontaneous activity in the cat E. Manjarrez * , G. Rojas-Piloni, D. Vazquez, A. Flores Instituto de Fisiologı ´a, Beneme ´rita Universidad Auto ´noma de Puebla, 14 sur 6301 Col. San Manuel, Apartado Postal 406, C.P. 72570 Puebla, Pue., Mexico Received 29 August 2001; received in revised form 12 November 2001; accepted 20 November 2001 Abstract Simultaneous recordings of cortical activity, recorded as the cortical local field potential (CLFP) in the contralateral posterior sigmoid gyrus, and the spinal activity, recorded as the cord dorsum potential (CDP) of the L6 lumbar segment, were made in the anaesthetized cat. The electrodes were positioned in somatosensory regions where the largest spon- taneous negative CLFPs and CDPs were recorded. We found that spontaneous negative CLFPs were preceded by spon- taneous negative CDPs with a mean latency of 14.4 ^ 3.5 ms. Amplitude of these spontaneous negative CLFPs was abolished after section of the dorsal columns and ipsilateral dorsolateral funiculus. It is concluded that the neurones of the primary somatosensory cortex can be driven by dorsal horn spinal neurones producing the spontaneous negative CDPs. This suggests very strongly that spontaneous neuronal activity in somatosensory regions of the brain is generated not only by ongoing activity of neurones located at supraspinal sites, but also by ongoing activity of spinal neurones. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Dorsal horn neurons; Somatosensory cortex; Background activity; Spontaneous cord dorsum potentials; Spontaneous activity A previous study [12] has shown that in the anaesthetized cat, the neuronal ensemble involved in the generation of the spontaneous negative cord dorsum potentials (CDPs) is located in the laminae III–VI, and modulates the synaptic transmission from segmental afferents. However, the influ- ence of this neuronal population on the spontaneous activity of cortical neurones, which are typically driven by thou- sands of synaptic inputs, was not clear. Although it is well known that cutaneous spinal informa- tion in cats may reach the cerebral cortex either through the dorsal columns or through other spinal pathways such as the spino-cervical projections in the dorsolateral funiculus [13– 15], the possibility that the neuronal ensemble involved in the generation of the spontaneous negative CDPs share the same ascending pathways has not been studied. The purpose of the present report was to present evidence that the cortical neurones can be driven by activity of dorsal horn spinal neurones producing the spontaneous negative CDPs through the dorsal columns and the ipsilateral dorsolateral funiculus. Guidelines contained in the National Institutes of Health publication on the Principles of Laboratory Animal Care 85- 23 revised in 1985 were followed throughout. Briefly, experi- ments were carried out using adult cats (2.5–3.5 kg) initially anaesthetized with pentobarbitone (35 mg kg 21 of weight, i.p). Most procedures were reported previously and are briefly described here [12]. A wide bilateral pneumothorax and a fixation-suspension of the vertebral column at the level equal to or slightly below the level of the exposed cortex were performed to reduce movements and to avoid cortical pulsa- tions [16]. The right surface of the skull was exposed and a trephine hole, 7 mm in diameter, was made over the soma- tosensory cortex, contralateral to the site of lesion of the dorsolateral funiculus (see below). The dura mater was care- fully removed, approximately 1 mm 2 in some experiments, but in others approximately 4 mm 2 was removed. A wall around the aperture in the bone was constructed from dental acrylic, and the well so formed was kept filled with Agar– Agar in order to provide additional stability of recordings. The microelectrode holder (piezoelectric Burleigh, 6000 ULN) allowed fast penetration of micropipettes without dimpling of the cortex. The incidence of edema was reduced by extreme care in the performance of surgical manipulations on the vicinity of the superior sagittal sinus [3,17,18]. Only Neuroscience Letters 318 (2002) 145–148 0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0304-3940(01)02497-1 www.elsevier.com/locate/neulet * Corresponding author. Tel.: 152-22-2244-1657; fax: 152-22- 2233-4511. E-mail address: emanjar@siu.buap.mx (E. Manjarrez).