Cross-correlation analysis of unit activity in spinal locomotor centers

Correlation analysis of unit activity in spinal locomotor centers was carried out in immobilized thalamic cats. Within a short time interval (the time shift of one spike train relative to the other during plotting of the cross-correlation histogram did not exceed 54 msec) correlation between the spike flows of these cells was absent, irrespective of the distance between them, both at rest and during efferent discharge generation. Spike flows of neurons could correlate only in the case of a long time interval (maximal time shift of one spike train relative to the other not less than 4–8 sec during plotting of the cross-correlation histogram). Weak correlation with a long time interval (4–8 sec) was found between changes in the momentary frequency of a neuron and the intensity of the discharge in the motor nerve, but no correlation was found between changes in momentary frequency of the neuron and intensity of discharge. The possible causes of the absence of correlation with a short time interval and its presence with a long time interval are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 283–289, May–June, 1980.     

Statistical characteristics of spontaneous and evoked unit activity in the cat superior colliculus

Spontaneous and evoked unit activity of the superior colliculus was studied in cats immobilized with gallamine or with the spinal cord divided (encephalé isolé). Statistical parameters of unit activity were calculated in light and darkness and in the presence of a moving photic stimulus. Spontaneously active neurons were divided into four main groups: 1) with a mean interspike interval of about 300 msec, coefficient of variation 1.9, and with two modes in the autocorrelation histogram; 2) with similar statistical parameters but distinguished by correlation with saccadic eye movements; 3) histogram of interspike intervals exponential in type, autocorrelation histogram flat, mean interval and standard deviation about 100 msec; 4) with symmetrical distribution of interspike intervals, mean interval about 50 msec, coefficient of variation 0.4–0.5. Spontaneous activity in light and darkness differed only in the neurons of the second group. Comparison of the statistical parameters of the spontaneous and evoked activity shows that encoding of the stimulus could be carried out by neurons of groups 3 and 4. In some cases the mode of the histogram of interspike intervals and the standard deviation changed significantly and activity appeared regularly in the autocorrelation histogram.     

Statistical analysis of unit activity in the cat motor cortex

Activity of 366 neurons in the motor area of the biceps brachii muscle was studied in chronic experiments on cats during an instrumental placing response. Of these cells, 59 received afferentation from the skin, joints, or deep structures of the limb participating in movement. Of 160 neurons which changed their discharge during the placing response, 52 (32.5%) had a peripheral input. Three types of motor cortical neurons are described: I) changing their discharge frequency before movement began, II) after movement began, and III) before and during movement. Positive correlation (r=0.3926) was found between the presence of a peripheral input for the neurons studied and changes in discharge frequency during the placing response. Correlation between the presence of a concrete input in the neurons and the type to which they belonged was studied.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 201–207, May–June, 1979.     

Individual characteristics of spontaneous locomotor activity and adaptive behavior in the rat

Spontaneous locomotor activity (SLA) of the male rats possesses significant individual differences. The daily volume of this activity is sufficiently stable for each separate individual. Animals with high and low SLA also differ in daily dynamics of this parameter. The behaviour of the rats with low SLA was characterized by lesser orienting activity and greater emotional reactivity in comparison to the rats with high SLA. By means of factor analysis it was established that, along with searching activity, emotional reactivity and alimentary motivation, the need in motor activity is one of the main inner factors, determining various manifestations of adaptive behaviour.     

Modulation of SK channels regulates locomotor alternating bursting activity in the functionally-mature spinal cord

The spinal cord contains specialized groups of cells called pattern generators, which are capable of orchestrating rhythmic firing activity in an isolated preparation. Different patterns of activity could be generated in vitro including right-left alternating bursting and bursting in which both sides are synchronized. The cellular and network mechanisms that enable these behaviors are not fully understood. We have recently shown that Ca²⁺-activated K⁺ channels (SK channels) control the initiation and amplitude of synchronized bursting in the spinal cord. It is unclear, however, whether SK channels play a similar role in the alternating rhythmic pattern. In the current study, we used a spinal cord preparation from functionally mature mice capable of weight bearing and walking. The present results extend our previous work and show that SK channel inhibition initiates and modulates the amplitude of alternating bursting. We also show that addition of methoxamine, an α₁-adrenergic agonist, to a cocktail of serotonin, dopamine, and NMDA evokes robust and consistent alternating bursting throughout the cord.     

Initiation of locomotor activity in spinalized cats by epidural stimulation of the spinal cord]

An area initiating locomotor activity under conditions of the spinal cord surface stimulation (SCS) was found at the upper border of the lumbar enlargement (L4-5 spinal segments). Parameters of the SCS for activation of the spinal stepping generator (SSG) were identified. Activation of the SSG under the SCS was shown to occur because of interaction of the spinal and peripheral mechanisms. Primary role in the SSG initiation during the SCS belongs to the propriospinal system of the dorsolateral funiculi.     

Self-organizing effects of spontaneous neural activity on the development of spinal locomotor circuits in vertebrates

Presented in this paper is a neural network model that can be used to investigate the possible self-organizing mechanisms occurring during the early ontogeny of spinal neural circuits in the vertebrate motor system. The neural circuit is composed of multiple types of neurons which correspond to motorneurons, Renshaw cells and a hypothetical class of interneurons. While the connectivity of this circuit is genetically predetermined, the efficacies of these connections – the synaptic s trengths – evolve in accordance with activity-dependent mechanisms which are initiated by the intrinsic, autonomous activity present in the developing spinal cord. Using Oja's rule, a modified Hebbian learning scheme for adjusting the values of the connections, the network stably self-organizes developing, in the process, reciprocally activated motorneuron pools analogous to those which exist in vivo. Received: 30 December 1996 / Accepted in revised form: 20 June 1997     

Genetic identification of spinal interneurons that coordinate left-right locomotor activity necessary for walking movements

The sequential stepping of left and right limbs is a fundamental motor behavior that underlies walking movements. This relatively simple locomotor behavior is generated by the rhythmic activity of motor neurons under the control of spinal neural networks known as central pattern generators (CPGs) that comprise multiple interneuron cell types. Little, however, is known about the identity and contribution of defined interneuronal populations to mammalian locomotor behaviors. We show a discrete subset of commissural spinal interneurons, whose fate is controlled by the activity of the homeobox gene Dbx1, has a critical role in controlling the left-right alternation of motor neurons innervating hindlimb muscles. Dbx1 mutant mice lacking these ventral interneurons exhibit an increased incidence of cobursting between left and right flexor/extensor motor neurons during drug-induced locomotion. Together, these findings identify Dbx1-dependent interneurons as key components of the spinal locomotor circuits that control stepping movements in mammals.     

Masking of locomotor activity in hamsters

The inhibition of locomotion by light (masking) was investigated in Syrian hamsters. When 1-h pulses of light were presented in the early night, activity was strongly suppressed by irradiances of about 1 lx or greater. Ultradian light-dark cycles were used as another way to study masking. Hamsters were unable to entrain to 3.5:3.5-h light-dark cycles, thus permitting the masking and the entraining effects of light to be distinguished. Light had greater suppressive effects on activity in home cages than on activity in novel running wheels. Moreover, in home cages activity remained very low for about 30 min after lights were turned off. Post-pulse suppression of activity was not simply a consequence of reduced running, as shown by experiments in which running was temporarily prevented by locking the wheels. A phase response curve for masking was obtained by placing hamsters in novel wheels for 3-h periods at various times throughout their circadian cycles, and then superimposing a 30-min light pulse. The suppressive effect of light was maximal around the onset of activity, which normally coincides with dusk in hamsters. This may have adaptive value in limiting foraging to the hours of darkness. Accepted: 8 February 1999     

Pineal and locomotor activity

Summary Perch-hopping activity patterns of pinealectomized and normal house sparrows,Passer domesticus, were examined by power spectral analysis and by analysis of daily totals. Power spectral analysis strengthened our previous conclusion that circadian periodicity is absent from the activity of pinealectomized birds kept in constant conditions. The spectral analyses also revealed that obvious ultradian rhythms are not present in sparrow perching activity. Pinealectomy had no effect on the daily activity totals.     

Analysis of locomotor activity rhythms in Drosophila

The genetic, molecular and anatomical dissection of the circadian clock in Drosophila and other higher organisms relies on the quantification of rhythmic phenotypes. Here, we introduce the methods currently in use in our laboratories for the analysis of fly locomotor activity rhythms. This phenotype provides a relatively simple, automated, efficient, reliable and robust output for the circadian clock. Thus it is not surprising that it is the preferred readout for measuring rhythmicity under a variety of conditions for most fly clock laboratories. The procedure requires at least 10 days of data collection and several days for analysis. In this protocol we advise on fly maintenance and on experimental design when studying the genetics of behavioral traits. We describe the setup for studying locomotor activity rhythms in the fruit fly and we introduce the statistical methods in use in our laboratories for the analysis of periodic data.     

Development and functional organization of spinal locomotor circuits

The coordination and timing of muscle activities during rhythmic movements, like walking and swimming, are generated by intrinsic spinal motor circuits. Such locomotor networks are operational early in development and are found in all vertebrates. This review outlines and compares recent advances that have revealed the developmental and functional organization of these fundamental spinal motor networks in limbed and non-limbed animals. The comparison will highlight common principles and divergence in the organization of the spinal locomotor network structure in these different species as well as point to unresolved issues regarding the assembly and functioning of these networks.