Convergence of nociceptive and non-nociceptive inputs onto spinal reflex pathways to the tibialis anterior muscle in humans

To investigate whether the familial clustering of cutaneous melanoma is consistent with Mendelian inheritance of a major autosomal gene, maximum likelihood segregation analyses were performed in a population-based sample of 1,912 families ascertained through a proband with melanoma diagnosed in Queensland between 1982 and 1990. Analyses were performed with the S.A.G.E. statistical package, using the REGTL program for a binary trait with a variable age of onset. We sought medical confirmation for all family members reported to have had melanoma, and only medically verified cases among relatives were included in the analyses. The hypothesis of codominant Mendelian inheritance gave a significantly better fit to the data than either dominant or recessive Mendelian inheritance, or environmental transmission. Overall, both Mendelian inheritance of a single major gene, and purely environmental transmission were rejected (P < 0.001). In both the single major gene and environmental models, there was strong evidence of familial dependence in melanoma occurrence (P < 0.001). These results are consistent with reported genetic heterogeneity in melanoma inheritance and suggest that other familial factors, such as pigmentation, skin type, and sun exposure habits, may play an important role in the familial clustering of melanoma.     

Spinal branching of corticospinal axons in the cat

Branching patterns of single corticospinal (CS) neurons were studied in the cat by activating these neurons antidromically from various regions of the spinal cord. 1. One hundred and ninety-three neurons were activated antidromically by microstimulation in the gray substance of the cervical cord and the majority of them were found in the forelimb area of the pericruciate cortex. 2. Branches to the lower levels of the spinal cord were found for 30% of the neurons projecting to the cervical gray matter. 3. The remaining 70% sent axons only to the cervical gray matter and some of them sent multiple branches to several segments in the cervical cord. 4. Only a few CS neurons located outside of the forelimb area could be activated from the cervical cord, but all of them also sent branches to the lower levels of the spinal cord. Neurons projecting to both the cervical cord and the lower levels were intermingled in the cortex with those projecting only to the cervical cord. 5. CS neurons activated from a given area of the cervical cord were often clustered together in a small area of the cortex, although some of these CS neurons sent their other branches to other parts of the spinal cord and neurons projecting to other parts were also intermingled among them. 6. The functional significance of multiple axonal branching of CS neurons is discussed in relation to cortical motor functions.     

Brain stem and primary afferent projections to the ventromedial group of propriospinal neurones in the cat

The preparation of charcoal-gelatin disks and their use for removing free steroid in radioimmunoassays are described. Plasma concentrations of several steroids were determined using charcoal-gelatin disks or charcoal suspension and the results are compared. The advantages of using charcoal-gelatin disks are discussed.     

Convergence of the descending pathways of motor, visual and limbic cortex in the cat di- and mesencephalon

Comparisons of the descending pathways of the motor, visual and limbic cortex in the cat revealed a number of structures in di- and mesencephalon that receive projections from all these fields. They are centrolateral (CL), paracentral (Pc), central medial (CeM) and centre median (CM), nuclei of the thalamus, zona incerta (ZI) and Forel's field H1 of the subthalamus, nucleus of the posterior commissure and anterior and posterior nuclei of the pretectum (Prt), stratum griseum intermedial and profundum of superior colliculus (CS), periaqueductal gray matter (GC) and pontine nuclei (NP). The projections from the striate field of the visual cortex to ventrobasal complex of the thalamus (VB) are shown. The results are discussed with recent data on the anatomy and physiology. A possible role of corticocortical and corticofugal fiber connections is dealt with.     

Cutaneous nociceptive facilitation of Ib heteronymous pathways to lower limb motoneurones in humans

The effects of tonic pain stimulation on heteronymous Ib pathways from the gastrocnemius medialis (GM) to the soleus (Sol) and to the quadriceps (Q) muscles were investigated in four healthy human subjects. Tonic pain stimulation was performed by subcutaneous injection of 0.5 mg levo-ascorbic acid or vitamin C (L-LAS) in a volume of 0.5 ml on the dorsal surface of the ipsilateral foot. The mean curve of L-AS-induced pain sensation showed a steep rising phase reaching maximum intensity at 2-3 min, followed by a slow decay phase lasting about 15-20 min. Between about 5 and 20 min after injection, there was evidence of pure pain stimulation due to chemical activation of free nerve endings. During this interval, significant potentiation of Ib inhibition from GM to both Sol and Q motoneurones was observed. The time-course of these Ib heteronymous changes paralleled that of subjective pain sensation. These findings demonstrate that nociceptive discharge modifies the gain of Ib heteronymous effects in humans. Since the man function of these Ib pathways is to coordinate activity of muscles operating at different joints, it is suggested that nociceptive input may change muscle synergies by selecting specific subpopulations of Ib interneurones, thus contributing to establish appropriate adaptive motor strategies.     

The location of cardiac vagal preganglionic motoneurones in the medulla of the cat

1. Electrophysiological techniques have been used to locate the origin of preganglionic vagal motoneurones supplying the heart of the cat. 2. The right cardiac vagal branches were identified anatomically and their ability to slow the heart was assessed by electrical stimulation. Control experiments revealed that contamination of cardiac branches by bronchomotor and oesophageal efferent fibres was likely to be small. 3. Fifty-seven neurones in the medulla were activated antidromically on stimulating the cardiac branches at up to 5 times the threshold for cardiac slowing. They had axons with conduction velocities between 3 and 15 m/sec, corresponding to B fibres. 4. None of these were located in the region of the dorsal motor nucleus of the vagus, in spite of repeated sampling there, but all were located in the region of the nucleus ambigus. Histological examination of marked neurones (forty-six of the fifty-seven neurones) revealed that they were associated with its principal column, rostral to the obex. 5. Sampling motoneurones of the dorsal motor nucleus revealed that most sent axons down the thoracic vagus below the cardiac branches. Only three of thirty-three could be activated antidromically by high intensity stimulation of the cardiac branches, but on the basis of their thresholds and conduction velocities, it is argued that they were unlikely to be cardio-inhibitory neurones. 6. It is concluded that preganglionic cardio-inhibitory neurones arise not in the dorsal motor nucleus, but in the principal column of the nucleus ambiguus.     

On the phasic reflex bronchodilation in the cat

In records of tracheal pressure or flow taken from anesthetized cats appear large pressure-negative, or air inflow excursions, in response to single pulses applied to the central end of the vagus nerve. These responses have been attributed to phasic bronchodilation and not only due to the brief contractions of inspiratory muscles that occur as part of the total responses. Phasic bronchodilation responses appear mainly during inspiration but they may also occur in the expiratory phase through facilitation, during post-hyperventilatory apnea or that induced by constant current (d.c.) vagal stimulation. They are significantly reduced after lung sympathectomy. These bronchomotor responses showed long term depression (LTD) after spontaneous or reflexly evoked hiccups, and long term potentiation (LTP) after repetitive, or d.c. vagal stimulation. They are also potentiated on the experimental conditions that include exaggerated sympathetic activity. These and some other characteristics described indicate that bronchomotor responses are legitimate and can be used to follow the changes in excitability of the central generator of breathing.     

Fluctuations of excitability in the monosynaptic reflex pathway to lumbar motoneurons in the cat

1. It is well known that the amplitude of successive monosynaptic reflexes (MSR), elicited by afferent stimuli of constant strength, fluctuate from trial to trial. Previous evidence suggests that such excitability fluctuations within the motor pool can be introduced either pre- and/or postsynaptically. Using unanesthetized decerebrate or decerebrate/spinal cats, we attempted to evaluate the relative importance of pre- and postsynaptic mechanisms to MSR variability and the potential contribution of changes in the identities of responding motoneurons to such variability. 2. Comparisons between the MSR amplitude, measured in a severed ventral root, and the probability of firing of up to three individual motoneurons in fine filaments teased from the same root, confirmed that both correlated and uncorrelated fluctuations of motoneuron excitability are involved in MSR variability. Linear regression analysis from concurrent intracellular recordings from homonymous motoneurons showed that the MSR fluctuations were correlated with the variations in membrane potential baseline, as well as with the fluctuations in the monosynaptic excitatory postsynaptic potential peak amplitude. In all 11 cases tested, the former correlation was stronger than the latter. 3. Stimulation of the caudal cutaneous sural nerve (CCS) was used to alter the postsynaptic potential background on which triceps surae (GS) MSRs were generated. The interval chosen between CCS conditioning and the GS stimulation excluded the involvement of presynaptic inhibition. When conditioned by preceding CCS stimulation, GS population MSRs generally (8/9 cases tested) increased in amplitude without much change in their overall variance. However, the individual motoneurons that contributed to the population responses did show changes in both relative excitability and in the uncorrelated component of their response variance. About half of the concurrently recorded motoneurons (6/13) showed a decrease in relative excitability after CCS conditioning, 5/13 showed an increase, and 2/13 were unchanged. Comparison of unit and population responses indicated that the identities of the motoneurons that responded at any given level of population response were quite different with and without CCS conditioning. 4. High-frequency stimulation of Ia fibers was used to alter the state of presynaptic Group Ia-afferents that produced population MSRs. Post tetanic potentiation following high-frequency stimulation did not greatly alter the variance of population MSRs or ratio of correlated and uncorrelated fluctuations in MSR responses among individual motoneurons within the responding population. However, intratetanic depression and posttetanic potentiation of population MSRs were accompanied by marked shifts in individual motoneuron excitability relative to the population response, again indicated that changes in the identities of responding motoneurons contributes to population response fluctuations.(ABSTRACT TRUNCATED AT 400 WORDS)     

Stimulatory and inhibitory effects of serotonergic hallucinogens on spinal mono- and polysynaptic reflex pathways in the rat

The effects of two 5-HT-related hallucinogens on rat spinal mono- and polysynaptic reflex pathways in the rat were investigated. 5-Methoxy-N,N-dimethyltryptamine (5-MeODMT, 1 and 100 micrograms/kg, i.v.), an indolealkylamine agent, produced a dose-dependent decrease in the monosynaptic reflex, whereas 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI, 1-100 micrograms/kg), a phenylalkylamine agent, produced a dose-dependent increase in the monosynaptic reflex. Both agents increased the polysynaptic reflex. The 5-HT2 receptor antagonists ketanserin (100 micrograms/kg) and ritanserin (100 micrograms/kg) blocked the effects of DOI on the monosynaptic reflex but only partially blocked the 5-MeODMT-induced effect on the monosynaptic reflex. These antagonists inhibited the change in polysynaptic reflex, induced by DOI but not by 5-MeODMT. Neither propranolol (1 mg/kg) nor 3-tropanyl-3,5-dichlorobenzoate (MDL 72222, 1 mg/kg) antagonized the effect of either agent. 5-Methoxy-N,N-dimethyltryptamine and DOI increased the excitability of motoneurons and this effect was inhibited by ketanserin. These results indicate that the two types of hallucinogens possess both common and distinct characteristics, with regard to their action on the spinal reflex: (1) both increase the activity of motoneurons through 5-HT2 receptors but (2) only 5-MeODMT has an inhibitory action on the pathway of the monosynaptic reflex.     

Activity of motoneurons during fictitious scratch reflex in the cat

(1) Intracellular recording of motoneurons of different hindlimb muscles: tibialis anterior (TA), gastrocnemius and soleus (GS), vastus crureus (Vast), posterior biceps and semitendinosus (PBSt), was carried out during the fictitious scratch reflex in decerebrate cats. (2) During the postural stage of the reflex, a depolarizaiton (3.8 mV on average) was observed in TA motoneurons accompanied by tonic discharge. No change of the membrane potential (MP) and no discharge were observed during this stage in GS, Vast and PBSt motoneurons. (3) In the rhythmical stage of the reflex, the MP of TA motoneurons changed only slightly during the 'long' (L) phase of the scratch cycle and remained at approximately the same level as during the postural stage. In this phase, motoneurons discharged at frequencies of 20-100 pps. In the 'short' (S) phase of the scratch cycle a strong repolarization occurred, the MP reached the same level as observed during resting conditons (MP0), and the discharge discontinued. (4) GS motoneurons were gradually depolarized during the second half of the L-phase. The depolarization reached its maximum (5.5 mV on average in relation to the MP0) on average in relation to the MP0) in the S-phase, and several action potentials were generated with intervals of 5-10 msec. Then, at the beginning of the L-phase, the motoneurons were repolarized and the MP reached the level of the MP0. The behavior of Vast motoneurons was essentially similar to that of GS motoneurons. (5) The PBSt motoneurons usually had two peaks of depolarization per cycle--in the S-phase and at the beginning of the L-phase. The maximal depolarization was 3.5 mV (on average). The motoneurons generated action potentials at one or both peaks of depolarization. (6) The possible organization of the central influences upon motoneurons of different muscles during scratching is discussed.     

Reversal of fusimotor reflex responses during locomotion in the decerebrate cat

The effect of brief trains of electrical stimulation, at 2, 3 and 20 x threshold (T), of cutaneous afferents in the medial plantar nerve on the discharges of single medial gastrocnemius static and dynamic gamma-efferents has been investigated at rest and during locomotion in a decerebrate cat preparation. The units were classified as dynamic (10 units) or static (10 units) indirectly on the basis of their resting and locomotor discharge characteristics. Responses were assessed by calculating the change in mean gamma-rate during the 100 ms after stimulus onset compared with a control period. At rest, most dynamic neurones were inhibited by stimulation at 2T (9 of 10 units) and above. In contrast, the resting responses of most static neurones were excitatory at 2T (9 of 10 units) and 3T, while 20T produced static gamma-effects that varied in sign. During locomotion the responses of both types of gamma-efferent were phase related. Two patterns were observed with dynamic units. For seven dynamic neurones, at stimulus levels of 2T (7 units) and above, responses during electromyogram (EMG) bursts were inhibitory while those between bursts were not significantly different from zero. However, for three other dynamic units, a phase-related reversal of reflex responses was observed at some stimulus intensities (always 2T, 3 units) comprising inhibition during, and excitation between, EMG bursts. For static neurones, inhibitory (never excitatory) responses occurred during walking at stimulus intensities of 2T (10 units) and above. The locomotor responses of static units were maximum during (3 units) or between (7 units) EMG bursts and were minimum in the opposite phase of EMG activity. A task-related reversal of reflex responses was thus generally apparent (9 of 10 units) to low intensity stimulation (2T) for static gamma-efferents during locomotion (inhibition) compared with rest (excitation). During locomotion there was a significant linear relation between the magnitude of response and the background gamma-rate for static units and those dynamic units that did not exhibit phase-related reflex reversal (total, 17 units). For dynamic gamma-efferents, inhibition at rest and during locomotion occurred at short (spinal) latencies which were not significantly different and are consistent with the involvement of the same interneuronal pathway. We conclude that pathways of opposite sign may dominate the responses of fusimotor neurones to low threshold cutaneous afferents from the plantar surface of the foot depending on behavioural context. Furthermore, the cutaneous reflex responses of both types of gamma-motoneurones during locomotion appear to vary with the source of the afferent input and do not constitute a general excitatory drive. The results are discussed in relation to the role and reflex control of the fusimotor system.     

Contribution of vestibular commissural pathways to spatial orientation of the angular vestibuloocular reflex

During nystagmus induced by the angular vestibuloocular reflex (aVOR), the axis of eye velocity tends to align with the direction of gravito-inertial acceleration (GIA), a process we term "spatial orientation of the aVOR." We studied spatial orientation of the aVOR in rhesus and cynomolgus monkeys before and after midline section of the rostral medulla abolished all oculomotor functions related to velocity storage, leaving the direct optokinetic and vestibular pathways intact. Optokinetic afternystagmus and the bias component of off-vertical-axis rotation were lost, and the aVOR time constant was reduced to a value commensurate with the time constants of primary semicircular canal afferents. Spatial orientation of the aVOR, induced either during optokinetic or vestibular stimulation, was also lost. Vertical and roll aVOR time constants could no longer be lengthened in side-down or supine/prone positions, and static and dynamic tilts of the GIA no longer produced cross-coupling from the yaw to pitch and yaw to roll axes. Consequently, the induced nystagmus remained entirely in head coordinates after the lesion, regardless of the direction of the resultant GIA vector. Gains of the aVOR and of optokinetic nystagmus to steps of velocity were unaffected or slightly increased. These results are consistent with a model in which the direct aVOR pathways are organized in semicircular canal coordinates and spatial orientation is restricted to the indirect (velocity storage) pathways.     

Ascending pressor and depressor pathways in the cat spinal cord

Blood pressure responses to stimulation of the cervical dorsolateral sulcus (DLS) of the spinal cord and lumbar dorsal roots were studied in anesthetized, vagotomized, and paralyzed cats. Stimulation of the lumbar dorsal roots elicited pressor responses with high-frequency stimulation (50 Hz, 10 V, 1 ms) and depressor responses with low-grequency stimulation (1 Hz, 10 V, 1 ms). Pressor responses were converted to depressor responses after bilateral lesions were made in the DLS area rostral to the site of stimulation. These results suggest that the ascending spinal pressor pathways are localized in the DLS region. Furthermore, these depressor responses were abolished by placing additional bilateral lesions in the dorsolateral funiculus (DLF) rostral to the site of stimulation. These data indicate the presence of ascending depressor pathways in the DLF which are anatomically separate from pressor pathways. Both pathways were found to be bilateral systems, and decussation of fibers appears to be complete within three segments rostral to their entry into the spinal cord. Ascending depressor pathways have a low optimal frequency of activation, as opposed to the ascending pressor pathways which have a relatively high optimal frequency of activation. Neurophysiological evidence obtained by recording unit activity from the cervical sympathetic trunk confirmed the localization of the ascending pressor and depressor pathways.     

Convergence properties of solitary tract neurons responsive to cardiac receptor stimulation in the anesthetized cat

The convergence pattern of cardiac receptors, pulmonary C-fibers, carotid chemoreceptor, and baroreceptor afferents onto neurons within the nucleus of the solitary tract (NTS) was studied in the anesthetized (pentobarbitone sodium, 40 mg/kg,) paralyzed and artificially ventilated cat. Extra- and intracellular recordings were made from NTS neurons while stimulating both cardiac receptors by aortic root injections of veratridine (1-3 micrograms/kg) and pulmonary C-fibers by a right atrial injection of phenylbiguanide (10-20 micrograms/kg). The ipsilateral carotid body was stimulated by using arterial injection of CO2-saturated bicarbonate solution, whereas inflation of the ipsilateral carotid sinus was used to activate baroreceptors. The ipsilateral cardiac vagal branch, cervical vagus, and carotid sinus nerves were stimulated electrically (1 Hz, 0.2-1 ms, 1-35 V). In 78 NTS neurons recorded either extracellularly (n = 47) or intracellularly (n = 31), electrical stimulation of the cardiac branch of the vagus nerve evoked synaptic potentials (spikes and/or excitatory postsynaptic potentials) with an onset latency between 4 and 220 ms. Some neurons displayed both short and long latency inputs(15.5 +/- 1.8 and 160.0 +/- 8.5 ms; n = 14). Of these 78 neurons, 24 responded to veratridine stimulation of cardiac receptors (i.e., cardioreceptive neurons) by exhibiting an augmenting-decrementing discharge of 37 +/- 4 s in duration with a peak frequency of 30 +/- 5 Hz. Convergence from other cardiorespiratory receptors was noted involving either carotid chemoreceptors (n = 7) or pulmonary C-fibers (n = 4) or from both carotid chemoreceptors and pulmonary C-fibers (n = 6). In contrast, only one cardioreceptive NTS neuron was activated by distension of the carotid sinus. Recording sites recovered were confined to the medial NTS at the level of the area postrema and extended caudally into the commissural subnucleus. Our results indicate a convergence of carotid chemoreceptor and pulmonary C-fiber afferent inputs to cardioreceptive NTS neurons. With the paucity of baroreceptor inputs to these neurons it is suggested that sensory integration within the NTS may reflect regulatory versus defensive or protective reflex control.     

Convergence and divergence of the signaling pathways for insulin and phosphoinositolglycans

Phosphoinositolglycan molecules isolated from insulin-sensitive mammalian tissues have been demonstrated in numerous in vitro studies to exert partial insulin-mimetic activity on glucose and lipid metabolism in insulin-sensitive cells. However, their ill-defined structures, heterogeneous nature, and limited availability have prohibited the analysis of the underlying molecular mechanism. Phosphoinositolglycan-peptide (PIG-P) of defined and homogeneous structure prepared in large scale from the core glycan of a glycosyl-phosphatidylinositol-anchored membrane protein from Saccharomyces cerevisiae has recently been shown to stimulate glucose transport as well as a number of glucose-metabolizing enzymes and pathways to up to 90% (at 2 to 10 microns) of the maximal insulin effect in isolated rat adipocytes, cardiomyocytes, and diaphragms (G. Müller et al., 1997, Endocrinology 138: 3459-3476). Consequently, we used this PIG-P for the present study in which we compare its intracellular signaling with that of insulin. The activation of glucose transport by both PIG-P and insulin in isolated rat adipocytes and diaphragms was found to require stimulation of phosphatidylinositol (PI) 3-kinase but to be independent of functional p70S6kinase and mitogen-activated protein kinase. The increase in glycerol-3-phosphate acyltransferase activity in rat adipocytes in response to PIG-P and insulin was dependent on both PI 3-kinase and p70S6kinase. This suggest that the signaling pathways for PIG-P and insulin to glucose transport and metabolism converage at the level of PI 3-kinase. A component of the PIG-P signaling pathway located up-stream of PI 3-kinase was identified by desensitization of isolated rat adipocytes for PIG-P action by combined treatment with trypsin and NaCl under conditions that preserved cell viability and the insulin-mimetic activity of sodium vanadate but completely blunted the insulin response. Incubation of the cells with either trypsin or NaCl alone was ineffective. The desensitized adipocytes were reconstituted for stimulation of lipogenesis by PIG-P by addition of the concentrated trypsin/salt extract. The reconstituted adipocytes exhibited 65-75% of the maximal PIG-P response and similar EC50 values for PIG-P (2 to 5 microns) compared with control cells. A proteinaceous N-ethylmaleimide (NEM)-sensitive component contained in the trypsin/salt extract was demonstrated to bind in a functional manner to the adipocyte plasma membrane of desensitized adipocytes via bipolar interactions. An excess of trypsin/salt extract inhibited PIG-P action in untreated adipocytes in a competitive fashion compatible with a receptor function for PIG-P of this protein. The presence of the putative PIG-P receptor protein in detergent-insoluble complexes prepared from isolated rat adipocytes suggests that caveolae/detergent-insoluble complexes of the plasma membrane may play a role in insulin-mimetic signaling by PIG-P. Furthermore, treatment of isolated rat diaphragms and adipocytes with PIG-P as well as with other agents exerting partially insulin-mimetic activity, such as PI-specific phospholipase C (PLC) and the sulfonylurea glimepiride, triggered tyrosine phosphorylation of the caveolar marker protein caveolin, which was apparently correlated with stimulation of lipogenesis. Strikingly, in adipocytes subjected to combined trypsin/salt treatment, PIG-P, PI-specific PLC, and glimepiride failed completely to provoke insulin-mimetic effects. A working model is presented for a signaling pathway in insulin-sensitive cells used by PIG(-P) molecules which involves GPI structures, the trypsin/salt- and NEM-sensitive receptor protein for PIG-P, and additional proteins located in caveolae/detergent-insoluble complexes.     

Sacral glutamatergic transmission in the descending limb of the micturition reflex in the cat

This study was undertaken to clarify the location of glutamatergic synaptic transmission in the descending pathway of the micturition reflex in decerebrate cats. Contractions of the urinary bladder evoked by stimulating the pontine micturition center were completely inhibited by the broad-spectrum excitatory amino acid antagonist, kynurenic acid (KYN) and the selective N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, that were applied intrathecally to the sacral cord, while such contractions were not attenuated by the non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). An iontophoretic application of KYN remarkably inhibited discharges of the sacral parasympathetic preganglionic neurons innervating the urinary bladder (bladder motoneurons) elicited by pontine stimulation. Our results suggest that glutamatergic synaptic transmission is located at the level of the sacral cord in the descending limb of the micturition reflex and is mediated via NMDA receptor on the bladder motoneurons.     

Recovery of forelimb placing after lateral hypothalamic lesions in the cat: Parallels and contrasts with development.

Recovery of forelimb placing after lateral hypothalamic lesions in the cat (20 Ss) was similar in several respects to the development of placing in kittens (5 Ss). In both recovery and development, the sequence in which sensory systems acquired control over placing was the same: vestibular—proprioceptive— tactile—visual. In addition, within each sensory modality, placing was initially sluggish, exaggerated in amplitude, and susceptible to rapid habituation. Unlike development, however, the recovery of visually guided placing did not require visuomotor experience. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential spinal projections from the forelimb areas of the rostral and caudal subregions of primary motor cortex in the cat

We used anterograde transport of WGA-HRP to examine the topography of corticospinal projections from the forelimb areas within the rostral and caudal motor cortex subregions in the cat. We compared the pattern of these projections with those from the somatic sensory cortex. The principal finding of this study was that the laminar distribution of projections to the contralateral gray matter from the two motor cortex subregions was different. The rostral motor cortex projected preferentially to laminae VI-VIII, whereas caudal motor cortex projected primarily to laminae IV-VI. Confirming earlier findings, somatic sensory cortex projected predominantly to laminae I-VI inclusive. We found that only rostral motor cortex projected to territories in the rostral cervical cord containing propriospinal neurons of cervical spinal segments C3-4 and, in the cervical enlargement, to portions presumed to contain Ia inhibitory interneurons. We generated contour maps of labeling probability on averaged segmental distributions of anterograde labeling for all analyzed sections using the same algorithm. For rostral motor cortex, heaviest label in the dorsal part of lamina VII in the contralateral cord was consistently located in separate medial and lateral zones. In contrast, no consistent differences in the mediolateral location of label was noted for caudal motor cortex. To summarize, laminae I-III received input only from the somatic sensory cortex, while laminae IV-V received input from both somatic sensory and caudal motor cortex. Lamina VI received input from all cortical fields examined. Laminae VII-IX received input selectively from the rostral motor cortex. For motor cortex, our findings suggest that projections from the two subregions comprise separate descending pathways that could play distinct functional roles in movement control and sensorimotor integration.