Effects of dorsal root section and occlusion of dorsal spinal artery on the neurotransmitter candidates in rat spinal cord

In order to obtain further evidence of putative neurotransmitters in primary sensory neurons and interneurons in the dorsal spinal cord, we have studied the effects of unilateral section of dorsal roots and unilateral occlusion of the dorsal spinal artery on cholinergic enzyme activity and on selected amino acid levels in the spinal cord. One week after sectioning dorsal roots from caudal cervical (C₇) to cranial thoracic (T₂) levels, the specific activity of choline acetyltransferase (ChAT) was significantly decreased and acetylcholinesterase (AChE) showed a tendency to decrease in the dorsal quadrant on the operated side of the spinal cord. Dorsal root sectioning had little effect on the levels of free glutamic acid or other amino acids in the dorsal spinal cord. These results suggest that primary sensory neurons may include some cholinergic axons, and that levels of putative amino acid transmitters are not regulated by materials supplied by axonal transport from the dorsal root ganglia. By contrast, one week following unilateral occlusion of the dorsal spinal artery, the activities of ChAT and AChE were unchanged in the operated quadrant of the spinal cord, while decreases of Asp, Glu, and GABA, and an increase in Tau were detected. These findings are consistent with the proposals that such amino acids, but not ACh, may function as neurotransmitter candidates in interneurons of the dorsal spinal cord.Abbreviation used ACh acetylcholine - AChE acetylcholinesterase - Asp aspartic acid - ChAT choline acetyltransferase - GABA -aminobutyric acid - Glu glutamic acid - Gly glycine - SP substance P - Tau taurine     

Axonal remodeling for motor recovery after traumatic brain injury requires downregulation of ��-aminobutyric acid signaling

Remodeling of the remnant neuronal network after brain injury possibly mediates spontaneous functional recovery; however, the mechanisms inducing axonal remodeling during spontaneous recovery remain unclear. Here, we show that altered γ-aminobutyric acid (GABA) signaling is crucial for axonal remodeling of the contralesional cortex after traumatic brain injury. After injury to the sensorimotor cortex in mice, we found a significant decrease in the expression of GABA_AR-α1 subunits in the intact sensorimotor cortex for 2 weeks. Motor functions, assessed by grid walk and cylinder tests, spontaneously improved in 4 weeks after the injury to the sensorimotor cortex. With motor recovery, corticospinal tract (CST) axons from the contralesional cortex sprouted into the denervated side of the cervical spinal cord at 2 and 4 weeks after the injury. To determine the functional implications of the changes in the expression of GABA_AR-α1 subunits, we infused muscimol, a GABA R agonist, into the contralesional cortex for a week after the injury. Compared with the vehicle-treated mice, we noted significantly inhibited recovery in the muscimol-treated mice. Further, muscimol infusion greatly suppressed the axonal sprouting into the denervated side of the cervical spinal cord. In conclusion, recovery of motor function and axonal remodeling of the CST following cortical injury requires suppressed GABA_AR subunit expression and decreased GABAergic signaling.     

正常中国人中枢运动系统传导时间的测定

本文应用高电压、低输出阻抗刺激器,经皮给予大脑皮层和脊髓电刺激(BSPES),同时在上肢鱼际(Thenar)和下肢胫骨前肌(Muscle tibialis anterior)上记录诱发肌肉动作电位,测定了64名正常健康中国人(男:46;女:18)的中枢运动系统传导时间。受试者年龄为20—67岁,身高为156—185cm。刺激大脑皮层出现反应的潜伏期与刺激脊髓出现反应的潜伏期之差为中枢运动传导时间(CMCT)。实验测得鱼际的 CMCT 为6.69±1.48ms;胫骨前肌的 CMCT 为12.90±1.59ms。经统计学处理证明,CMCT 与左右侧肢体、性别、年龄及身高无关。说明 CMCT 是无损伤测定与评价中枢运动系统功能的较精确的一种客观指标。本文根据所测数据,计算出脊髓内运动传导速度为71.34±10.89 m/s,与文献报道的锥体束传导速度50—70 m/s 相近。因此,CMCT 反映了锥体束的传导时间。     

Cholinergic input is required during embryonic development to mediate proper assembly of spinal locomotor circuits

Rhythmic limb movements are controlled by pattern-generating neurons within the ventral spinal cord, but little is known about how these locomotor circuits are assembled during development. At early stages of embryogenesis, motor neurons are spontaneously active, releasing acetylcholine that triggers the depolarization of adjacent cells in the spinal cord. To investigate whether acetylcholine-driven activity is required for assembly of the central pattern-generating (CPG) circuit, we studied mice lacking the choline acetyltransferase (ChAT) enzyme. Our studies show that a rhythmically active spinal circuit forms in ChAT mutants, but the duration of each cycle period is elongated, and right-left and flexor-extensor coordination are abnormal. In contrast, blocking acetylcholine receptors after the locomotor network is wired does not affect right-left or flexor-extensor coordination. These findings suggest that the cholinergic neurotransmitter pathway is involved in configuring the CPG during a transient period of development.     

Partial cloning and expression of mRNA coding choline acetyltransferase in the spinal cord of the goldfish, Carassius auratus

Choline acetyltransferase (ChAT, EC 2.3.1.6) synthesizes a neurotransmitter, acetylcholine in cholinergic neurons. ChAT is considered to be the most specific marker for cholinergic neurons. To obtain a better marker of the neurons, as the first step, we isolated a partial ChAT cDNA from the goldfish (Carassius auratus) brain by RT-PCR methods. The partial cDNA of the goldfish ChAT was composed of 718 nucleotides. The amino acid sequence of the goldfish ChAT is approximately 70% identical to those of mammalian and chicken ChAT. Northern blot analysis demonstrated that ChAT mRNA was expressed in the brain and the spinal cord of the goldfish, and much abundant in the spinal cord. In the spinal cord of the goldfish, ChAT-positive neurons were detected mainly in the ventral horn by in situ hybridization. In addition, fluorescence in situ hybridization combined with a retrograde labeling by using True Blue demonstrated ChAT mRNA positive neurons were exactly motoneurons. In the cord, putative presynaptic sympathetic neurons were also labeled.     

Experiments on the central pattern generator for swimming in amphibian embryos

The central nervous system of paralysed Xenopus laevis embryos can generate a motor output pattern suitable for swimming locomotion. By recording motor root activity in paralysed embryos with transected nervous systems we have shown that: (a) the spinal cord is capable of swimming pattern generation; (b) swimming pattern generator capability in the hindbrain and spinal cord is distributed; (c) caudal hindbrain is necessary for sustained swimming output after discrete stimulation. By recording similarly from embryos whose central nervous system was divided longitudinally into left and right sides, we have shown that: (a) each side can generate rhythmic motor output with cycle periods like those in swimming; (b) during this activity cycle period increases within an episode, and there is the usual rostrocaudal delay found in swimming; (c) this activity is influenced by sensory stimuli in the same way as swimming activity; (d) normal phase coupling of the left and right sides can be established by the ventral commissure in the spinal cord. We conclude that interactions between the antagonistic (left and right) motor systems are not necessary for swimming rhythm generation and present a model for swimming pattern generation where autonomous rhythm generators on each side of the nervous system drive the motoneurons. Alternation is achieved by reciprocal inhibition, and activity is initiated and maintained by tonic excitation from the hindbrain.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.     

Effect of Motor and Premotor Cortex Ablation on Concentrations of Amino Acids, Monoamines, and Acetylcholine and on the Ultrastructure in Rat Striatum. A Confirmation of Glutamate as the Specific Cortico-Striatal Transmitter

At 1, 2, and 4 weeks after unilateral premotor and motor cortex ablation in rats, a significant and lasting decrease in glutamate levels in the ipsilateral versus contralateral striatum was observed. A significant corresponding fall in aspartate was seen only after 1 week. In contrast, there was a large increase in the striatal concentrations of lysine, threonine, alanine, and glutamine 1 week after the cortical ablation. This correlates with the extensive glial proliferation in the deafferented ipsilateral striatum. Four weeks after cortical ablation the GABA concentration was significantly increased. There was no decrease in other putative transmitters (dopamine, serotonin, acetylcholine, glycine and taurine), nor was a glutamate decrease observed in the hippocampus or in the hypothalamus, which do not receive direct premotor and motor cortical inputs. Both biochemical and morphological evidence for a minor contralateral cortico-striatal projection was obtained. Correlating with the fall in glutamate, ultrastructural observations indicated the degeneration of two types of striatal synapses, i.e., those of the axo-spinous type III and of the axo-dendritic type VII. Frontal cortex ablation clearly affects, in opposite directions, the metabolism of various striatal amino acids but not that of acetylcholine and the monoamine transmitters. The results strongly support the view that glutamate is the transmitter of the cortico-striatal fibers.     

Cervical sprouting of corticospinal fibers after thoracic spinal cord injury accompanies shifts in evoked motor responses.

The adult central nervous system (CNS) of higher vertebrates displays a limited ability for self repair after traumatic injuries, leading to lasting functional deficits [1]. Small injuries can result in transient impairments, but the mechanisms of recovery are poorly understood [2]. At the cortical level, rearrangements of the sensory and motor representation maps often parallel recovery [3,4]. In the sensory system, studies have shown that cortical and subcortical mechanisms contribute to map rearrangements [5,6], but for the motor system the situation is less clear. Here we show that large-scale structural changes in the spared rostral part of the spinal cord occur simultaneously with shifts of a hind-limb motor cortex representation after traumatic spinal-cord injury. By intracortical microstimulation, we defined a cortical area that consistently and exclusively yielded hind-limb muscle responses in normal adult rats. Four weeks after a bilateral transsection of the corticospinal tract (CST) in the lower thoracic spinal cord, we again stimulated this cortical field and found forelimb, whisker, and trunk responses, thus demonstrating reorganization of the cortical motor representation. Anterograde tracing of corticospinal fibers originating from this former hind-limb area revealed that sprouting greatly increased the normally small number of collaterals that lead into the cervical spinal cord rostral to the lesion. We conclude that the corticospinal motor system has greater potential to adapt structurally to lesions than was previously believed and hypothesize that this spontaneous growth response is the basis for the observed motor representation rearrangements and contributes to functional recovery after incomplete lesions.     

Increased Low-Frequency Oscillation Amplitude of Sensorimotor Cortex Associated with the Severity of Structural Impairment in Cervical Myelopathy

Decreases in metabolites and increased motor-related, but decreased sensory-related activation of the sensorimotor cortex (SMC) have been observed in patients with cervical myelopathy (CM) using advanced MRI techniques. However, the nature of intrinsic neuronal activity in the SMC, and the relationship between cerebral function and structural damage of the spinal cord in patients with CM are not fully understood. The purpose of this study was to assess intrinsic neuronal activity by calculating the regional amplitude of low frequency fluctuations (ALFF) using resting-state functional MRI (rs-fMRI), and correlations with clinical and imaging indices. Nineteen patients and 19 age- and sex-matched healthy subjects underwent rs-fMRI scans. ALFF measurements were performed in the SMC, a key brain network likely to impaired or reorganized patients with CM. Compared with healthy subjects, increased amplitude of cortical low-frequency oscillations (LFO) was observed in the right precentral gyrus, right postcentral gyrus, and left supplementary motor area. Furthermore, increased z-ALFF values in the right precentral gyrus and right postcentral gyrus correlated with decreased fractional anisotropy values at the C2 level, which indicated increased intrinsic neuronal activity in the SMC corresponding to the structural impairment in the spinal cord of patients with CM. These findings suggest a complex and diverging relationship of cortical functional reorganization and distal spinal anatomical compression in patients with CM and, thus, add important information in understanding how spinal cord integrity may be a factor in the intrinsic covariance of spontaneous low-frequency fluctuations of BOLD signals involved in cortical plasticity.     

The influence of BT-melanin on the recovery of conditioned instrumental reflexes in rats surviving after ablation of the sensorimotor cortex

It has been shown the reinforcement of the corticofugal plasticity in adult rats after unilateral ablation of sensorimotor cortex accompanied by intramuscular injections of low concentrations of BT-melanin. In result the process of compensatory recovery in rats central nervous system is accelerated, confirmable by the rapid recovery of previously elaborated instrumental conditioned reflex in comparison with the control animals. It is assumed that the compensation of the motor deficit arised after the sensorimotor cortex ablation is ensured by the ability of two main motor systems of the brain (corticospinal and corticorubrospinal) to duplicate each other. This phenomenon of functional switching of descending influences has also been revealed in control group rats, not injected with BT-melanin. However the difference in time periods of operantly conditioned reflex recovery, for experimental and control groups, argues the apparent acceleration of this process, induced by the effects of BT-melanin. The obtained data considers the possibility of applied use of low concentrations of BT-melanin.     

Expression of nerve growth factor receptor mRNA is developmentally regulated and increased after axotomy in rat spinal cord motoneurons

In situ hybridization histochemistry and RNA blot analysis were used to study expression of nerve growth factor receptor (NGF-R) mRNA in rat spinal cord motoneurons. The results show that NGF-R mRNA is expressed at high levels in rat spinal cord motoneurons at the time of naturally occurring cell death. This expression is sustained, but reduced, during synapse formation and is subsequently greatly reduced in the adult spinal cord. A unilateral crush lesion of the sciatic nerve resulted in an 8-fold increase in NGF-R mRNA in adult rat spinal cord motoneurons 3 days after lesion, compared with the nonlesioned side. NGF-R mRNA induction was even more pronounced 7 and 14 days after lesion, reaching levels 12 times higher than those on the nonlesioned side. However, 6 weeks after lesion, when the motor function of the leg was largely restored, NGF-R expression had decreased to levels similar to those on the contralateral side. We therefore suggest that NGF-R mediates a trophic or axonal guidance function for developing and regenerating spinal cord motoneurons.     

Effect of tetanus toxin on the content of glycine, gamma-aminobutyric acid, glutamate, glutamine and aspartate in the rat spinal cord

Tetanus toxin injected intramuscularly induced no significant changes in the levels of glycine, GABA, glutamate, glutamine or aspartate in extracts of spinal cord from rats killed at timed intervals during the development of local and generalized tetanus. The amino acid contents in the hemisegment (longitudinal one-half) of the spinal cord (L₂-L₆) on the injected side (left gastrocnemius muscle) did not differ significantly from the contents in the hemisegment of the spinal cord on the non-injected side. Nor were there any consistent changes in the contents of the amino acids in either hemisegment of the spinal cord as the tetanic symptoms became progressively more severe. Hence, the amino acid pool in the spinal cord was relatively stable despite the metabolic changes known to occur in tetanus. Our observations are consistent with the view of Johnston , De Groat and CURTIS (1969) who suggested that if glycine were indeed a spinal inhibitory neurotransmitter released by interneurons affected by tetanus toxin, the toxin should interfere with the release of the amino acid rather than deplete the transmitter stores.     

Disruption of food-getting movements after removal of the motor or premotor zone of the cerebral cortex in cats]

Instrumental food-procuring movements were studied in cats before and after unilateral or bilateral ablation of the motor or premotor cortical area. It is shown that unilateral impairment of the motor area affects the strength and accuracy of movements of the contralateral fore-leg, whereas the ablation of the premotor area leads to a slowing down of movements and breaking of a goal-directed movement into separate components. Bilataral ablation of the motor area irreversibly abolished the instrumental reflex. The ablation of the premotor cortex destroyed the animal's reaction to the sound signal, but food-procuring movements of the fore-legs were disturbed only temporarily. The obtained data are discussed on the basis of the concept that in cats the above cortical areas play different roles in the organization of goal directed behaviour.     

Cortical control of tongue protrusion and lateral movements in the cat

Based on area P lesion experiments, we hypothesized that tongue protrusion adapted for licking might be regulated by the lateral wall of the presylvian sulcus (bilateral areas P) of the cerebral cortex (Hiraba H, Sato T, Nakakawa K, Ueda K. . Cortical control of appropriate tongue protrusion during licking in cats—Increase in regional cerebral blood flow (rCBF) of the contralateral area P and in tongue protrusion after the unilateral area P lesion. Somatosens Mot Res 26:82–89). We propose that the right and left lingual muscles are dominated by the right and left hypoglossal nucleus, respectively, and that right and left pyramidal cells projecting to the right and left hypoglossal nucleus, respectively, exist in unilateral area P. These cells project via an inhibitory interneuron relay to the lateral branches toward the left or right pyramidal cells in contralateral area P. In this study, we aimed to demonstrate the existence of inhibitory interneurons using injections of a gamma-aminobutyric acid (GABA) agonist (muscimol), a GABA antagonist (bicuculline), and kainic acid into unilateral area P, followed by examination of tongue protrusion and lateral movements during trained licking and changes in regional cerebral blood flow (rCBF) values in the contralateral area P. We found disordered protrusion toward both sides and a marked decrease in rCBF values in the contralateral area P after bicuculline injection. We also found abnormal tongue protrusion toward the front and a marked increase in rCBF values after muscimol and kainic acid injections. These results suggest that cortical networks between the bilateral areas P are relayed by inhibitory interneurons.     

Chronological Observations of Primary Somatosensory Cortical Maps in Kittens following Low Thoracic (T12) Spinal Cord Transection at 2 Weeks of Age

The present study investigated the reorganization of the somatosensory cortex in kittens following T₁₂ spinal cord transection at 2 weeks of age. Multiunit electrophysiological methods were used to map the somatosensory cortex of kittens at 3, 6, and 9 weeks after the transection. The entire reorganized cortical region was driven by substitute cutaneous inputs, primarily from the trunk, at 3 weeks after spinal cord transection. Although the level of cortical responsiveness remained the same throughout the 9 weeks studied, internal trunk representation changed, and there was an increase in shoulder girdle representation and emergence of forelimb representation. Poor somatotopic and topographic order was observed in the reorganized cortex, regardless of time posttransection. Finally, trunk receptive fields displayed a wide variety of shapes, sizes, and orientations not seen in the normal cortex.     

Glycine Binding to Rat Cortex and Spinal Cord: Binding Characteristics and Pharmacology Reveal Distinct Populations of Sites

Glycine is the principal inhibitory neurotransmitter in posterior regions of the brain. In addition, glycine serves as an allosteric regulator of excitatory neurotransmission mediated by the N-methyl-D-aspartate (NMDA) acidic amino acid receptor subtype. The studies presented here characterize [3H]glycine binding to washed membranes prepared from rat spinal cord and cortex, areas enriched in glycine inhibitory and NMDA receptors, respectively, in an attempt to define the glycine recognition sites on the two classes of receptors. Specific binding for [3H]glycine was seen in both cortex and spinal cord. Saturation analyses in cortex were best fitted by a two-site model with respective equilibrium dissociation constants (KD values) of 0.24 and 5.6 microM and respective maximal binding constants (Bmax values) of 3.4 and 26.7 pmol/mg of protein. Similar analyses in spinal cord were best fitted by a one-site model with a KD of 5.8 microM and Bmax of 20.2 pmol/mg of protein. Na+ had no effect on [3H]glycine binding to cortical membranes but increased the binding to spinal cord membranes by greater than 15-fold. This Na+-dependent binding may reflect glycine binding to the recognition site of the high-affinity, Na+-dependent glycine uptake system. Several short-chain, neutral amino acids displaced [3H]glycine binding from both cortical and spinal cord membranes. The most potent displacers of [3H]glycine binding to cortical membranes were D-serine and D-alanine, followed by the L-isomers of serine and alanine and beta-alanine. In contrast, D-serine and D-alanine were similar in potency to L-serine in spinal cord membranes. Compounds active at receptors for the acidic amino acids had disparate effects on the binding of [3H]glycine. At 10 microM, NMDA resulted in a 25% increase, whereas D- and L-2-amino-5-phosphonovaleric acid at 100 microM resulted in a 30% decrease, in [3H]glycine binding to cortical membranes. Kynurenic acid was the most potent of the acidic amino acid-related compounds at displacing [3H]glycine binding. In cortical membranes, kynurenic acid displacement was resolved into a high- and a low-affinity component; the high-affinity component displaced the high-affinity component of [3H]glycine binding.(ABSTRACT TRUNCATED AT 400 WORDS)     

Spatial organization of direct connections of the sensomotor cortex with the rhombencephalon and spinal cord in the cat

The distribution and ultrastructure of terminals of corticofugal fibers in the rhombencephalon and spinal cord of the cat were studied by light and electron microscopy at various times (4–6 days) of experimental degeneration after extensive or local (about 3 mm in diameter) destruction of the sensomotor cortex. Definite topographical organization of corticofugal projections in the nuclei of the dorsal columns and in the spinal cord was detected by the Fink — Heimer method. After local destruction of the lateral zones of the sensomotor cortex, maximal foci of degeneration were found in the nucleus of Burdach and the lateral basilar region of the cervical segments; after local destruction of the medial zones of the sensomotor cortex maximal foci of degeneration of corticofugal fibers were observed in Goll's nucleus and the lateral basilar region of the lumbar segments. The results show that even an extremely localized area of the cat sensomotor cortex forms two separate systems of descending corticospinal fibers. The first projects into the dorsolateral and dorsomedial parts of the intermediate zone, chiefly contralaterally, whereas the second projects bilaterally into both dorsolateral and ventromedial parts of the intermediate zone. The possible physiological significance of this duality of projections is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 126–133, March–April, 1976.     

Areal Distributions of Cortical Neurons Projecting to Different Levels of the Caudal Brain Stem and Spinal Cord in Rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Ag_m), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb.

The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI. Injections in lateral SI representing the face produced dense terminal label in the contralateral trigeminal complex. Injections in cortex devoted to the forelimb and forepaw labeled the contralateral cuneate nucleus and parts of the dorsal horn of the spinal cord. The cortical injections also demonstrated interconnections of parts of SI with some of the other regions of cortex with projections to the spinal cord, and provided further evidence for the existence of PV in rats.