Death of american ground sloths

Organic remains, especially dung, of extinct ground sloths provide ideal material for radiocarbon dating. Rampart Cave, Arizona, revealed periodic occupation at intervals by the Shasta ground sloth from before 40,000 years ago until 11,000 years ago. Dates from other caves in the arid Southwest indicate that the Shasta ground sloth disappeared at very soon after the time of Clovis big game hunters. Ground sloth remains in South America are slightly younger. The timing of ground sloth extinction is in accord with the model of explosive overkill.     

Cryptoses choloepi: A Coprophagous Moth That Lives on a Sloth

The larvae of the sloth moth, Cryptoses choloepi, live in the dung of the three-toed sloth, Bradypus infuscatus. Adult female moths apparently leave the fur of the sloth to oviposit when the sloth descends, once a week, to the forest floor to defecate. Newly emerged moths fly from the dung pile into the forest canopy to find a sloth.     

颈部脊髓硬膜外电刺激治疗脑性瘫痪的临床观察

目的：观察颈部脊髓硬膜外电刺激治疗脑性瘫痪的临床疗效。方法：采用C2--C5脊髓硬膜外电刺激治疗脑性瘫痪病人18例，具体参数为：频率25—100ppm，强度3—15V，波宽0．3--0．4ms，时间6h／d。结果：18例病人中15例有效。结论：颈部脊髓硬膜外电刺激是一种治疗脑性瘫痪病人有效方法。     

双峰驼跗关节解剖

解剖成年双峰驼跗关节８个，结果发现双峰驼跗关节在形态结构方面有以下显著特征：１．中央跗骨不与第四跗骨融合；２．距骨近端具嵴状滑车，远端具髁状滑车，近端滑车的嵴和沟向前内侧倾斜，与矢状面间的夹角为１０°，远端滑车的髁和沟朝向正前方，双重滑车结构使跗关节伸屈运动范围加大，并能进行一定程度的侧向运动，这是骆驼驮载重物时能够自由起卧的重要原因之一；３．具有跟踱外侧韧带，而牛马均缺如；４．跗关节外侧短韧带从外侧踝达于跟骨，牛的从外侧踝至距骨，马的则从外侧踝达跟骨和距骨；５．跗背侧韧带位于内侧面，形成内侧侧副韧带之一部分。     

Leishmania braziliensis isolated from sloths in Panama

Two edentates, the twotoed sloth Choloepus hoffmanni and the three-toed sloth Bradypus infuscatus, infected with Leishmania were found in Panama. The rates of infection were 14.1 and 1.3 percent in Choloepus and Bradypus, respectively. Leishmania braziliensis sensu lato was cultured from skin, blood, spleen, liver, or bone marrow of 13 sloths often from two or more tissues from the same animal. This strain is indistinguishable from Leishmania strains isolated from hunmanis in Panama.     

Neuronal circuit mediating escape responses in crayfish

The neuronal circuit underlying rapid abdominal flexion in response to phasic tactile stimulation comprises identified afferents, interneurons of two orders, a decision unit, and several motor neurons. The circuit is organized hierarchically as a " cascade" in which electrical synapses predominate at higher levels. Behavioral habituation results from lability at chemical junctions early in the pathway.     

Release of coordinated behavior in crayfish by single central neurons

By stimulating and recording from the same interneuron at two separate points, we have shown that coordinated output to the postural abdominal muscles of crayfish can be produced by electrical stimulation of a single cell. Several central neurons can individually initiate one type of movement(for example, flexion),each producing a unique abdominal geometry.     

Computations underlying the execution of movement: a biological perspective

To execute voluntary movements, the central nervous system must transform the neural representation of the direction, amplitude, and velocity of the limb, represented by the activity of cortical and subcortical neurons, into signals that activate the muscles that move the limb. This task is equivalent to solving an "ill-posed" computational problem because the number of degrees of freedom of the musculoskeletal apparatus is much larger than that specified in the plan of action. Some of the mechanisms and circuitry underlying the transformation of motor plans into motor commands are described. A central feature of this transformation is a coarse map of limb postures in the premotor areas of the spinal cord. Vectorial combination of motor outputs among different areas of the spinal map may produce a large repertoire of motor behaviors.     

Balanced inhibition and excitation drive spike activity in spinal half-centers

Many limb movements are composed of alternating flexions and extensions. However, the underlying spinal network mechanisms remain poorly defined. Here, we show that the intensity of synaptic excitation and inhibition in limb motoneurons varies in phase rather than out of phase during rhythmic scratchlike network activity in the turtle. Inhibition and excitation peak with the total neuron conductance during the depolarizing waves of scratch episodes. Furthermore, spike activity is driven by depolarizing synaptic transients rather than pacemaker properties. These findings show that balanced excitation and inhibition and irregular firing are fundamental motifs in certain spinal network functions.     

Hydraulic compression of mice to 166 atmospheres

Hydraulic uniform compression elicited tremors, uncoordinated limb movements, and tonic convulsions in liquid-breathing mice at pressures ranging from 50 to 100 atmospheres. Such abnormal muscular activity was observed neither in control animals nor in mice caudally to a spinal transection. Uniform compression of isolated preparations of mouse muscle in saline failed to contract at pressures up to 200 atmospheres.     

Role of EphA4 and EphrinB3 in local neuronal circuits that control walking

Local circuits in the spinal cord that generate locomotion are termed central pattern generators (CPGs). These provide coordinated bilateral control over the normal limb alternation that underlies walking. The molecules that organize the mammalian CPG are unknown. Isolated spinal cords from mice lacking either the EphA4 receptor or its ligand ephrinB3 have lost left-right limb alternation and instead exhibit synchrony. We identified EphA4-positive neurons as an excitatory component of the locomotor CPG. Our study shows that dramatic locomotor changes can occur as a consequence of local genetic rewiring and identifies genes required for the development of normal locomotor behavior.     

Anthropologists bet on their latest data in las vegas

Anthropologists need luck on their side when they search for key fossils or study monkeys in the wild, but their work can still hit the jackpot. That was clear at the 61 st annual meeting of the American Association of Physical Anthropology, which brought more than 800 anthropologists to Las Vegas in early April. Among the reports was one on new fossils of early hominids in Ethiopia and another on extinct giant sloth lemurs in Madagascar.     

Somatovisceral pathway: rapidly conducting fibers in the spinal cord

Fibers that respond to distension of hollow viscera and to mechanical stimulation of somatic structures were found primarily near the ventromedian fissure of the upper lumbar spinal cord. These fibers could be directly excited by electrical stimulation at C(1). The average conduction velocity for these fibers was 68.6 meters per second.     

Retrograde viral delivery of IGF-1 prolongs survival in a mouse ALS model

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal neuromuscular disease that is associated with the degeneration of spinal and brainstem motor neurons, leading to atrophy of limb, axial, and respiratory muscles. The cause of ALS is unknown, and there is no effective therapy. Neurotrophic factors are candidates for therapeutic evaluation in ALS. Although chronic delivery of molecules to the central nervous system has proven difficult, we recently discovered that adeno-associated virus can be retrogradely transported efficiently from muscle to motor neurons of the spinal cord. We report that insulin-like growth factor 1 prolongs life and delays disease progression, even when delivered at the time of overt disease symptoms.     

Visuomotor coordination in reaching and locomotion

Locomotion and reaching have traditionally been regarded as separate motor activities. In fact, they may be closely connected both from an evolutionary and a neurophysiological viewpoint. Reaching seems to have evolved from the neural systems responsible for the active and precise positioning of the limb during locomotion; moreover, it seems to be organized in the spinal cord. The motor cortex and its corticospinal outflow are preferentially engaged when precise positioning of the limb is needed during locomotion and are also involved during reaching and active positioning of the hand near objects of interest. All of these motor activities require visuomotor coordination, and it is this coordination that could be achieved by the motor cortex and interconnected parietal and cerebellar areas.     

Serotonin and octopamine produce opposite postures in lobsters

Serotonin and octopamine, injected into the circulation of freely moving lobsters and crayfish, produce opposite behavioral effects. Octopamine injection produces sustained extension of the limbs and abdomen; serotonin injection produces sustained flexion. Neurophysiological analyses show that these postures can be accounted for by opposing, coordinated effects of these amines on patterns of motoneuron activity recorded from the ventral nerve cord.     

Anterior-posterior guidance of commissural axons by Wnt-frizzled signaling

Commissural neurons in the mammalian dorsal spinal cord send axons ventrally toward the floor plate, where they cross the midline and turn anteriorly toward the brain; a gradient of chemoattractant(s) inside the spinal cord controls this turning. In rodents, several Wnt proteins stimulate the extension of commissural axons after midline crossing (postcrossing). We found that Wnt4 messenger RNA is expressed in a decreasing anterior-to-posterior gradient in the floor plate, and that a directed source of Wnt4 protein attracted postcrossing commissural axons. Commissural axons in mice lacking the Wnt receptor Frizzled3 displayed anterior-posterior guidance defects after midline crossing. Thus, Wnt-Frizzled signaling guides commissural axons along the anterior-posterior axis of the spinal cord.     

Stress-induced analgesia in humans: endogenous opioids and naloxone-reversible depression of pain reflexes

The cumulative effects of a repetitive stress induced by anticipation of pain (noxious foot shock) were studied on the threshold of a nociceptive flexion reflex of the lower limb. The threshold of the nociceptive reflex progressively increased with the repetition of the stress. This effect was reversed by naloxone, which even produced hyperalgesia, since a rapid and significant decrease in this threshold, below the initial values, was noted. Tha data provide evidence for involvement of endogenous opioids in the phenomenon of stress-induced analgesia in normal man.     

Decreased hippocampal inhibition and a selective loss of interneurons in experimental epilepsy

The occurrence of seizure activity in human temporal lobe epilepsy or status epilepticus is often associated with a characteristic pattern of cell loss in the hippocampus. An experimental model that replicates this pattern of damage in normal animals by electrical stimulation of the afferent pathway to the hippocampus was developed to study changes in structure and function that occur as a result of repetitive seizures. Hippocampal granule cell seizure activity caused a persistent loss of recurrent inhibition and irreversibly damaged adjacent interneurons. Immunocytochemical staining revealed unexpectedly that gamma-aminobutyric acid (GABA)-containing neurons, thought to mediate inhibition in this region and predicted to be damaged by seizures, had survived. In contrast, there was a nearly complete loss of adjacent somatostatin-containing interneurons and mossy cells that may normally activate inhibitory neurons. These results suggest that the seizure-induced loss of a basket cell-activating system, rather than a loss of inhibitory basket cells themselves, may cause disinhibition and thereby play a role in the pathophysiology and pathology of the epileptic state.     

From swimming to walking with a salamander robot driven by a spinal cord model

The transition from aquatic to terrestrial locomotion was a key development in vertebrate evolution. We present a spinal cord model and its implementation in an amphibious salamander robot that demonstrates how a primitive neural circuit for swimming can be extended by phylogenetically more recent limb oscillatory centers to explain the ability of salamanders to switch between swimming and walking. The model suggests neural mechanisms for modulation of velocity, direction, and type of gait that are relevant for all tetrapods. It predicts that limb oscillatory centers have lower intrinsic frequencies than body oscillatory centers, and we present biological data supporting this.