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PubMed1995

The development of quadrupedal locomotion in the kitten.

The development of bipedal treadmill locomotion and overground locomotion has previously been studied in the kitten; the development of quadrupedal treadmill locomotion has not. We evaluated and compared all three forms of locomotion in the normal kitten and present quantitative data comparing the development of quadrupedal treadmill and overground locomotion. Overground locomotion was studied from the day of birth to 5 months of age and quadrupedal treadmill locomotion was studied in the same animals from 9 weeks to 5 months of age. Treadmill locomotion was initiated postweaning, since it could not be reliably elicited without a food reward. Three locomotor characteristics (weight support, balance, and coordination between the forelimbs and the hindlimbs) were evaluated quantitatively. Kittens first consistently demonstrated overground steps with the ventral surface of their bodies supported above the walking surface throughout the entire step cycle during the second and third postnatal weeks. By 4 weeks of age, overground locomotion consistently showed full weight support and midline positioning of the hindquarters. Coordination between the forelimbs and the hindlimbs developed differently in the two forms of quadrupedal locomotion evaluated. During overground locomotion, the kittens initially used a single pattern in which only one limb was in swing at any time. As the kittens' weight support and trunk control improved, additional swing phase coordination patterns emerged and these patterns were correlated with the animals' ability to change speeds during locomotion. The consistency with which a dominant interlimb swing phase pattern was used at a particular speed increased with age and, by 6 weeks, the frequency of each speed-related dominant pattern approached 100% during overground locomotion. At 6 weeks, interlimb coordination also was evident in the nearly consistent interlimb phase interval present between the forelimb's initiation of the first extension subphase and the ipsilateral hindlimb's initiation of the flexion phase. The consistent patterns appeared to be fostered by maturation of weight support and balance. In contrast, the interlimb phase interval was inconsistent during quadrupedal treadmill locomotion until 20 weeks of age. Moreover, the interlimb swing phase patterns used during quadrupedal treadmill locomotion differed from those used during overground locomotion. The differences in the developmental time course and patterns of interlimb coordination between overground and quadrupedal treadmill locomotion suggest that different mechanisms regulate the control of interlimb coordination during these two different forms of quadrupedal locomotion.

Age Factors↗
PubMed1998

The frequency of rat's hippocampal theta rhythm is related to the speed of locomotion.

Hippocampal EEG activity was recorded in rats during locomotion, spontaneous or induced by electrical stimulation of subthalamic locomotor region (SLR) and posterior hypothalamus (PH). Spontaneous locomotion was associated with the theta frequency (6-8.5 Hz). Electrically induced locomotion was also associated with theta rhythm, frequency of which depended on the site of stimulation. Theta frequency during SLR evoked locomotion was almost the same as during spontaneous locomotion (7-9 Hz). PH induced locomotion was accompanied by higher theta frequency (9-11 Hz). Theta frequency and the speed of locomotion were positively correlated during spontaneous locomotion. During electrically induced locomotion the theta frequency was much higher than expected when related to the speed of spontaneous locomotion. The electrically evoked locomotion may result from activation of various systems. Stimulation of the SLR activates system responsible for the exploratory behavior, while stimulation of PH evokes locomotion related to aversive behavior. Thus, we conclude that the theta rhythm frequency may depend not only on the speed of locomotion but also on the rats' motivational-emotional state, associated with locomotion performed by the animal.

Animals↗
PubMed2003

Lung ventilation during treadmill locomotion in a terrestrial turtle, Terrapene carolina.

The limb girdles and lungs of turtles are both located within the bony shell, and therefore limb movements during locomotion could affect breathing performance. A mechanical conflict between locomotion and lung ventilation has been reported in adult green sea turtles, Chelonia mydas, in which breathing stops during terrestrial locomotion and resumes during pauses between bouts of locomotion. We measured lung ventilation during treadmill locomotion using pneumotach masks in three individual Terrapene carolina (mass 304-416 g) and found no consistent mechanical effects of locomotion on breathing performance. Relatively small tidal volumes (2.2+/-1.4 ml breath(-1); mean +/- S.D., N=3 individuals) coupled with high breath frequencies (36.6+/-26.4 breaths min(-1); mean +/- S.D., N=3 individuals) during locomotion yield mass-specific minute volumes that are higher than any previously reported for turtles (264+/-64 ml min kg(-1); mean +/- S.D., N=3 individuals). Minute volume was higher during locomotion than during recovery from exercise (P<0.01; paired t-test), and tidal volumes measured during locomotion were not significantly different from values measured during brief pauses between locomotor bouts or during recovery from exercise (P>0.05; two-way ANOVA). Since locomotion does not appear to conflict with breathing performance, the mechanism of lung ventilation must be either independent of, or coupled to, the stride cycle. The timing of peak airflow from breaths occurring during locomotion does not show any fixed phase relationship with the stride cycle. Additionally, the peak values of inhalatory and exhalatory airflow rates do not differ consistently with respect to the stride cycle. Together, these data indicate that T. carolina is not using respiratory-locomotor coupling and limb and girdle movements do not contribute to lung ventilation during locomotion. X-ray video recordings indicate that lung ventilation is achieved via bilateral activity of the transverse (exhalatory) and oblique (inhalatory) abdominal muscles. This specialized abdominal ventilation mechanism may have originally circumvented a mechanical conflict between breathing and locomotion in the ancestor of turtles and subsequently allowed the ribs to abandon their role in lung ventilation and to fuse to form the shell.

Abdominal Muscles↗
PubMed1992

Evidence for presynaptic dopamine mechanisms underlying amphetamine-conditioned locomotion.

Rats with a history of receiving (+)-amphetamine in a specific environment exhibit a conditioned psychomotor response when subsequently placed in that environment without drug treatment. Previous work has shown that while the unconditioned effects of amphetamine can be blocked by dopamine D1 or D2 receptor antagonists or with alpha-methyl-p-tyrosine, conditioned locomotion is not influenced by these treatments. In the present experiment, alpha-methyl-p-tyrosine (50 mg/kg, s.c.) was given in conjunction with amphetamine (1.5 mg/kg, s.c.) for 8 days before testing for conditioned locomotion. alpha-Methyl-p-tyrosine completely blocked amphetamine-induced locomotion but only attenuated amphetamine-conditioned locomotion. Reserpine (reduced over the 8 days from 2.5 to 1.25 mg/kg, i.p.) did not block amphetamine-induced locomotion; indeed, potentiation of amphetamine-induced locomotor activity was observed on the last 3 days of treatment. Reserpine treatment in conjunction with alpha-methyl-p-tyrosine treatment blocked amphetamine-induced locomotion for the first 4 days only, with full recovery of amphetamine-induced unconditioned locomotion by the last treatment day. Reserpine alone had no effect on amphetamine-conditioned locomotion, but completely blocked amphetamine-conditioned locomotion when given with alpha-methyl-p-tyrosine. It is concluded that the alpha-methyl-p-tyrosine-sensitive pool of dopamine mediates the immediate psychomotor effects of amphetamine, but that both the alpha-methyl-p-tyrosine- and reserpine-sensitive pools of dopamine are involved in the establishment of amphetamine-conditioned locomotion. In addition, the occurrence of amphetamine-conditioned locomotion is independent of the direct effects of amphetamine on locomotion.

Animals↗
PubMed2000

Depression of group Ia monosynaptic EPSPs in cat hindlimb motoneurones during fictive locomotion.

The effects of fictive locomotion on monosynaptic EPSPs recorded in motoneurones and extracellular field potentials recorded in the ventral horn were examined during brainstem-evoked fictive locomotion in decerebrate cats. Composite homonymous and heteronymous EPSPs and field potentials were evoked by group I intensity (<= 2T) stimulation of ipsilateral hindlimb muscle nerves. Ninety-one of the 98 monosynaptic EPSPs were reduced in amplitude during locomotion (mean depression of the 91 was to 66 % of control values); seven increased in amplitude (to a mean of 121 % of control). Twenty-one of the 22 field potentials were depressed during locomotion (mean depression to 72 % of control). All but 14 Ia EPSPs were smaller during both the flexion and extension phases of locomotion than during control. In 35 % of the cases there was < 5 % difference between the amplitudes of the EPSPs evoked during the flexion and extension phases. In 27 % of the cases EPSPs evoked during flexion were larger than those evoked during extension. The remaining 38 % of EPSPs were larger during extension. There was no relation between either the magnitude of EPSP depression or the locomotor phase in which maximum EPSP depression occurred and whether an EPSP was recorded in a flexor or extensor motoneurone. The mean recovery time of both EPSP and field potential amplitudes following the end of a bout of locomotion was approximately 2 min (range, < 10 to > 300 s). Motoneurone membrane resistance decreased during fictive locomotion (to a mean of 61 % of control, n = 22). Because these decreases were only weakly correlated to EPSP depression (r 2 = 0.31) they are unlikely to fully account for this depression. The depression of monosynaptic EPSPs and group I field potentials during locomotion is consistent with the hypothesis that during fictive locomotion there is a tonic presynaptic regulation of synaptic transmission from group Ia afferents to motoneurones and interneurones. Such a reduction in neurotransmitter release would decrease group Ia monosynaptic reflex excitation during locomotion. This reduction may contribute to the tonic depression of stretch reflexes occurring in the decerebrate cat during locomotion.

Animals↗
PubMed1991

The role of cutaneous afferents in the control of gamma-motoneurones during locomotion in the decerebrate cat.

1. The effect of electrical stimulation, up to 20x threshold (T), of the sural nerve on the discharges of single medial gastrocnemius static and dynamic gamma-motoneurones has been investigated at rest and during locomotion in the decerebrate cat. 2. A total of twenty-three gamma-motoneurones were recorded. The neurones were identified as static (15) or dynamic (8) on the basis of their discharge characteristics (Murphy, Stein & Taylor, 1984). 3. Low intensity stimulation (less than or equal to 1.5T) had no effect on the discharges of most (22 of 23) gamma-efferents at rest or during locomotion. Hence the largest afferents in the sural nerve had little influence on the discharges of static or dynamic gamma-motoneurones in either condition. 4. Higher intensity stimulation (greater than 1.5T) excited both types of gamma-efferent in the resting state and response size was graded with stimulus intensity. For most neurones (20 of 23) excitatory effects appeared in the range 1.5-2T. 5. Stimulation at intensities greater than 1.5T also excited dynamic and some static gamma-motoneurones during locomotion. The responses of dynamic gamma-motoneurones were unchanged during locomotion compared to the resting state. In contrast, the responses of static neurones were significantly reduced, or even abolished, during locomotion and stimuli less than or equal to 3T generally (12 of 13) had no effect. Thus the responses of static, but not dynamic, gamma-efferents were task dependent. Further, the thresholds of responses indicate that activation of low threshold mechanoreceptors in the sural receptive field excites both types of gamma-efferent at rest, and dynamic neurones during locomotion. In contrast, it is proposed that the same peripheral input does not affect static gamma-efferents during locomotion. 6. The responses of static and dynamic gamma-motoneurones during locomotion were not obviously related to step cycle phase, or gamma rate, and responses occurring during or between homonymous electromyogram (EMG) bursts were not significantly different. Thus gamma responses during locomotion were not phase dependent. 7. Stimulation at intensities greater than 3T excited dynamic and some static gamma-motoneurones during locomotion but simultaneously inhibited on-going EMG activity. Peripheral inputs are therefore capable of influencing alpha- and gamma-motoneurones independently during locomotion. 8. The significance of the results is discussed in relation to the control and function of gamma-motoneurones.

Animals↗
PubMed2003

Integration of motor and visual information in the parietal area 5 during locomotion.

The parietal cortex receives both visual- and motor-related information and is believed to be one of the sites of visuo-motor coordination. This study for the first time characterizes integration of visual and motor information in activity of neurons of parietal area 5 during locomotion under conditions that require visuo-motor coordination. The activity of neurons was recorded in cats during walking on a flat surface-a task with no visuo-motor coordination required (flat locomotion), walking along a horizontal ladder or a series of barriers-a task requiring visuo-motor coordination for an accurate foot placement on surface that is heterogeneous along the direction of progression (ladder and barriers locomotion), and walking along a narrow pathway-a task requiring visuo-motor coordination on surface homogeneous along the direction of progression (narrow locomotion). During flat locomotion, activity of 66% of the neurons was modulated in rhythm of stepping, usually with one peak per cycle. During ladder and barrier locomotion, the proportion of rhythmically active neurons significantly increased, their modulation became stronger, and the majority of neurons had two peaks of activity per cycle. During narrow locomotion, however, the activity of neurons was similar to that during flat locomotion. We concluded that, during locomotion, parietal area 5 integrates two types of information: signals about the activity of basic locomotion mechanisms and signals about heterogeneity of the surface along the direction of progression. We describe here the modes of integration of these two types of information during locomotion.

Action Potentials↗
PubMed1993

The effects of intrathecal administration of excitatory amino acid agonists and antagonists on the initiation of locomotion in the adult cat.

Development of pharmacological strategies for the control of locomotion in patients with spinal cord injury or disease requires an understanding of the neuroactive substances involved in the activation of the spinal cord neural systems for the control of locomotion. Studies using the in vitro preparations of the lamprey, frog embryo, and newborn rat indicate that excitatory amino acids (EAAs) are involved in the initiation of locomotion. The present study determines whether spinal EAA receptors play a role in locomotion in an in vivo, adult mammalian preparation. Experiments were performed on precollicular, postmammillary decerebrate cats, some of which were spinalized at the 13th thoracic segment. Cannulas for drug infusions were positioned intrathecally in the lumbar region of the spinal cord. A ligature around the spinal cord at the level of the 13th thoracic segment prevented rostral diffusion of the drugs. Locomotion was monitored with electromyograms in treadmill locomotion experiments and electroneurograms in fictive locomotion experiments. Intrathecal infusion of either the NMDA receptor antagonist 2-amino-5-phosphonovaleric acid or the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione blocked hindlimb treadmill and fictive locomotion induced by electrical stimulation of the mesencephalic locomotor region (MLR) of the midbrain. Intrathecal administration of NMDA elicited hindlimb fictive locomotion in resting animals similar to that evoked by electrical stimulation of the MLR. At lower concentrations, NMDA evoked either independent bursting activity in the various nerves or loosely organized rhythmicity showing little reciprocity between antagonists. In contrast, administration of the EAA uptake blocker dihydrokainic acid (DHK) evoked intermittent periods of bursting activity characterized by a variable duration and a high degree of reciprocity between flexors and extensors. Given together at low concentrations, NMDA and DHK produced a well-coordinated locomotor pattern. Kainate and quisqualate were ineffective in producing fictive locomotion. These results are consistent with the suggestion that EAAs play a role in the initiation of mammalian locomotion. Furthermore, the results are consistent with those obtained from the neonatal rat in vitro preparations.

2-Amino-5-phosphonovalerate↗
PubMed1991

Avian locomotion activated by brainstem infusion of neurotransmitter agonists and antagonists. I. Acetylcholine excitatory amino acids and substance P.

Previous studies have demonstrated that focal electrical stimulation of regions within the brainstem of a decerebrate bird will elicit all the normal patterns of avian locomotion. However, electrical stimulation can activate a variety of neuronal elements within the radius of effective current spread, including axons of passage traversing the stimulation point. To restrict activation to neuronal cell bodies within the immediate vicinity, we have utilized direct intracerebral injection of neurotransmitters, their agonists and antagonists, into identified brainstem locomotor regions. To undertake these studies, birds (geese or ducks) were placed in a stereotaxic frame and decerebrated under halothane anesthesia. After completion of surgery, several discrete locomotor regions were first identified with electrical microstimulation. Acetylcholine (ACh) and excitatory amino acid (EAA) agonists and antagonists, as well as Substance P were then slowly infused into each brainstem region. Any change in locomotor behavior was recorded by electromyographic techniques. When injected into a variety of sites, carbachol (an ACh nicotinic (AChN) and muscarinic (AChM) agonist) and pilocarpine (an AChM agonist) evoked locomotion, whereas atropine (an AChM antagonist) blocked locomotion. N-methyl-D-aspartate NMDA), but not glutamate, also elicited locomotion or reduced the current intensity threshold for electrically-evoked locomotion. The NMDA-induced locomotion evoked locomotion. The NMDA-induced locomotion could be blocked by the injection of glutamic acid diethyl ester (GDEE, an EAA antagonist) or D-2-amino-5-phosphonopentanoic acid (AP5) into the same site. Finally. Substance P also evoked locomotion. The above observations strongly suggest that brainstem electrically-stimulated locomotion in decerebrate birds is not due to activation of fibers traversing a brainstem locomotor region, but instead, is due to the activation of receptors located on neuronal cell bodies, dendrites or presynaptic terminals in the immediate vicinity of the micropipette tip. After correlating our findings with similar lamprey and mammalian studies, the comparable discoveries serve to underscore the suggestion that the neuroanatomical substrates underlying the brainstem control of locomotion appear to be highly conserved in all vertebrates.

Acetylcholine↗
PubMed1992

On the regulation of repetitive firing in lumbar motoneurones during fictive locomotion in the cat.

Repetitive firing of motoneurones was examined in decerebrate, unanaesthetised, paralysed cats in which fictive locomotion was induced by stimulation of the mesencephalic locomotor region. Repetitive firing produced by sustained intracellular current injection was compared with repetitive firing observed during fictive locomotion in 17 motoneurones. During similar interspike intervals, the afterhyperpolarisations (AHPs) during fictive locomotion were decreased in amplitude compared to the AHPs following action potentials produced by sustained depolarising current injections. Action potentials were evoked in 10 motoneurones by the injection of short duration pulses of depolarising current throughout the step cycles. When compared to the AHPs evoked at rest, the AHPs during fictive locomotion were reduced in amplitude at similar membrane potentials. The post-spike trajectories were also compared in different phases of the step cycle. The AHPs following these spikes were reduced in amplitude particularly in the depolarised phases of the step cycles. The frequency-current (f-I) relations of 7 motoneurones were examined in the presence and absence of fictive locomotion. Primary ranges of firing were observed in all cells in the absence of fictive locomotion. In most cells (6/7), however, there was no relation between the amount of current injected and the frequency of repetitive firing during fictive locomotion. In one cell, there was a large increase in the slope of the f-I relation. It is suggested that this increase in slope resulted from a reduction in the AHP conductance; furthermore, the usual elimination of the relation is consistent with the suggestions that the repetitive firing in motoneurones during fictive locomotion is not produced by somatic depolarisation alone, and that motoneurones do not behave as simple input-output devices during this behaviour. The correlation of firing level with increasing firing frequency which has previously been demonstrated during repetitive firing produced by afferent stimulation or by somatic current injection is not present during fictive locomotion. This lends further support to the suggestion that motoneurone repetitive firing during fictive locomotion is not produced or regulated by somatic depolarisation. It is suggested that although motoneurones possess the intrinsic ability to fire repetitively in response to somatic depolarisation, the nervous system need not rely on this ability in order to produce repetitive firing during motor acts. This capability to modify or bypass specific motoneuronal properties may lend the nervous system a high degree of control over its motor output.

Action Potentials↗
PubMed1985

Dopamine autoreceptors and the effects of drugs on locomotion and dopamine synthesis.

Criteria for distinguishing dopamine autoreceptor agonism from other mechanisms of inhibiting locomotion were examined, together with the relationship between inhibition of locomotion and dopamine synthesis. ED50 potencies to inhibit locomotion of mice were established for drugs from a number of categories. Spiperone 0.02 mg kg-1 significantly (P less than 0.05) reversed inhibition of locomotion by known dopamine agonists but not that by the other types of drug. Idazoxan antagonized inhibition of locomotion due to alpha 2-agonists but not dopamine agonists. RU 24926 (N-propyl-N,N-di[2-(3-hydroxyphenyl)ethyl]amine) was antagonized by both spiperone and idazoxan. Only for dopamine agonists was there good correlation (r = 0.97) between potencies to inhibit locomotion in mice and L-dihydroxyphenylalanine (L-DOPA) accumulation in the nucleus accumbens of rats treated with gamma-butyrolactone and 3-hydroxybenzylhydrazine. The specific dopamine D1-agonist, SK&F 38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine), was inactive in both tests at doses up to 10 mg kg-1. The mixed dopamine agonist/antagonist, (-)-3-(3-hydroxyphenyl)-N-propylpiperidine, commonly known as (-)-3-PPP, acted as a dopamine agonist in both tests but inhibited locomotion more potently than L-DOPA accumulation. The inhibitory effects of dopamine agonists on locomotion were not prevented by alpha-methyl-p-tyrosine pretreatment. The data suggest that spiperone-reversible inhibition of locomotion in mice is a good criterion for dopamine autoreceptor agonists. The receptors involved are affected by low doses of both dopamine agonists and antagonists and seem similar to those involved in the autoreceptor mediated inhibition of dopamine synthesis. However, inhibition of locomotion is not due simply to suppression of dopamine release brought about as a secondary consequence of effects on synthesis; a separate mechanism for inhibiting dopamine release is probably involved.

Animals↗