Decerebrate rigidity in animals

Variable impact of tizanidine on the medium latency reflex of upper and lower limbs

Sudden limb displacement evokes a complex sequence of compensatory muscle activity. Following the short-latency reflex and preceding voluntary reactions is an epoch termed the medium-latency reflex (MLR) that could reflect spinal processing of group II muscle afferents. One way to test this possibility is oral ingestion of tizanidine, an alpha-2 adrenergic agonist that inhibits the interneurons transmitting group II signals onto spinal motor neurons. We examined whether group II afferents contribute to MLR activity throughout the major muscles that span the elbow and shoulder. MLRs of ankle muscles were also tested during walking on the same day, in the same participants as well as during sitting in a different group of subjects. In contrast to previous reports, the ingestion of tizanidine had minimal impact on MLRs of arm or leg muscles during motor actions. A significant decrease in magnitude was observed for 2/16 contrasts in arm muscles and 0/4 contrasts in leg muscles. This discrepancy with previous studies could indicate that tizanidine's efficacy is altered by subtle changes in protocol or that group II afferents do not substantially contribute to MLRs.

Lower motor neuron findings after upper motor neuron injury: insights from postoperative supplementary motor area syndrome

Hypertonia and hyperreflexia are classically described responses to upper motor neuron injury. However, acute hypotonia and areflexia with motor deficit are hallmark findings after many central nervous system insults such as acute stroke and spinal shock. Historic theories to explain these contradictory findings have implicated a number of potential mechanisms mostly relying on the loss of descending corticospinal input as the underlying etiology. Unfortunately, these simple descriptions consistently fail to adequately explain the pathophysiology and connectivity leading to acute hyporeflexia and delayed hyperreflexia that result from such insult. This article highlights the common observation of acute hyporeflexia after central nervous system insults and explores the underlying anatomy and physiology. Further, evidence for the underlying connectivity is presented and implicates the dominant role of supraspinal inhibitory influence originating in the supplementary motor area descending through the corticospinal tracts. Unlike traditional explanations, this theory more adequately explains the findings of postoperative supplementary motor area syndrome in which hyporeflexia motor deficit is observed acutely in the face of intact primary motor cortex connections to the spinal cord. Further, the proposed connectivity can be generalized to help explain other insults including stroke, atonic seizures, and spinal shock.

A filmed hanging without decerebrate and decorticate rigidity: a case report and pathophysiological considerations

The study of filmed hangings in the recent has reveal a striking similarity in the agonal sequences, with a sequence of rapid loss of consciousness, convulsions, and then a complex pattern of decerebrate rigidity and decorticate rigidity. We report a case of filmed hanging not presenting with decerebrate and decorticate rigidity. A 52-year-old man stepped off a stool, hanging himself in a complete suspension in an upright position. The movement of the body stepping off the stool created a rotary movement around the ceiling's ring and the body of the hanging man immediately started to revolve around the ring. Apart for the rolling around the ceiling's ring, the body stayed motionless for the duration of the movie, without any evidence of decerebrate or decorticate rigidity. A review of the pathophysiology of these reflex posturing gives some insight as to the possible elucidation for their absence in this specific case.

Responses of feline medial medullary reticular formation neurons with projections to the C5–C6 ventral horn to vestibular stimulation

Prior studies have shown that the vestibular system contributes to adjusting respiratory muscle activity during changes in posture, and have suggested that portions of the medial medullary reticular formation (MRF) participate in generating vestibulo-respiratory responses. However, there was previously no direct evidence to demonstrate that cells in the MRF relay vestibular signals monosynaptically to respiratory motoneurons. The present study tested the hypothesis that the firing of MRF neurons whose axons could be antidromically activated from the vicinity of diaphragm motoneurons was modulated by whole-body rotations in vertical planes that stimulated vestibular receptors, as well as by electrical current pulses delivered to the vestibular nerve. In total, 171 MRF neurons that projected to the C5-C6 ventral horn were studied; they had a conduction velocity of 34+/-15 (standard deviation) m/sec. Most (135/171 or 79%) of these MRF neurons lacked spontaneous firing. Of the subpopulation of units with spontaneous discharges, only 3 of 20 cells responded to vertical rotations up to 10 degrees in amplitude, whereas the activity of 8 of 14 neurons was affected by electrical stimulation of the vestibular nerve. These data support the hypothesis that the MRF participates in generating vestibulo-respiratory responses, but also suggest that some neurons in this region have other functions.

Decerebration by global ischemic stroke in rats

In this study we present a fast and simple technique to decerebrate rats. By injecting polyvinylsiloxane (PVS) into both common carotid arteries we occluded the circle of Willis and all cerebral arteries, thereby completely interrupting the blood supply to the cerebrum. High viscosity PVS was used so that it only entered the large arteries, and did not pass into the capillary beds. This procedure reliably resulted in an anemic decerebration, without interfering with the blood supply to the brainstem. Long-term survival was achieved by reducing intracranial pressure by the application of steroids and/or opening the skull.

Hypothalamic-midbrain dysregulation syndrome: hypertension, hyperthermia, hyperventilation, and decerebration

Certain decerebrate lesions of brain stem or hypothalamus induce pharmacologically reversible hypertension and hyperthermia in animals. We observed three young patients with episodic decerebration, hyperthermia, hypertension, and hyperventilation during recovery from comas of different etiologies. The shared pathology on neurologic examinations and computed tomographic scans was hypothalamic-mesencephalic dysfunction, suggesting a diencephalic-brain-stem disconnection syndrome or brain-stem release mechanism. Propranolol was the most effective drug tested, but only two patients responded, one dramatically. This novel clinical syndrome may have localizing and therapeutic significance in pediatric coma that needs to be further defined in future studies.