Amadeo C. Nacimiento

Changes in regional energy metabolism after closed head injury in the rat

We examined in the present investigation regional ATP, glucose, and lactate content in the cortical and subcortical structures, in a rat model of closed head injury (CHI). In serial tissue sections bioluminescence imaging of ATP, glucose, and lactate was performed at 4 h, 12 h and 24 h (n=4/5 per time point with) after the induction of CHI or sham surgery. Bioluminescence images were analyzed by computer-assisted densitometry, at the lesion site, in remote cortical areas, and in the subcortical structures (thalamus and caudate nucleus). ATP content was significantly decreased at the lesion site after 4 h and in the remote cortex at 12 h post-injury. At 12 h, the ATP content reached baseline levels on the ipsilateral side and at 24 h also at remote lateral parietal sites. In the contralateral cortex, ATP increased transiently above the baseline at 12 h. No significant changes in ATP were found in the thalamus and caudate nucleus. Cortical glucose and lactate contents could not be discerned over time.Following CHI there is an acute and progressive, yet transient, ischemic cortical profile, which is not reflected in subcortical areas.

Immunocytochemistry of B-50 (GAP-43) in the spinal cord and in dorsal root ganglia of the adult cat.

SummaryThe distribution of the neural-specific growth associated protein B-50 (GAP-43), which persists in the mature spinal cord and dorsal root ganglia, has been studied by light and electron microscopic immunohistochemistry in the cat. Throughout the spinal cord, B-50 immunoreactivity was seen confined to the neuropil, whereas neuronal cell bodies were unreactive. The most conspicuous immunostaining was observed in the dorsal horn, where it gradually decreased from superficial laminae (I–II) toward more ventral laminae (III–V), and in the central portion of the intermediate gray (mainly lamina X). In these regions, the labelling was localized within unmyelinated, small diameter nerve fibres and axon terminals. In the rest of the intermediate zone (laminae VI–VIII), B-50 immunoreactivity was virtually absent. The intermediolateral nucleus in the thoracic and cranial lumbar cord showed a circumscribed intense B-50 immunoreactivity brought about by the labelling of many axon terminals on preganglionic sympathetic neurons. In motor nuclei of the ventral horn (lamina IX), low levels of B-50 immunoreactivity were present in a few axon terminals on dendritic and somal profiles of motoneurons. In dorsal root ganglia, B-50 immunoreactivity was mainly localized in the cell bodies of small and medium-sized sensory neurons. The selective distribution of persisting B-50 immunoreactivity in the mature cat throughout sensory, motor, and autonomie areas of the spinal cord and in dorsal root ganglia suggests that B-50-positive systems retain in adult life the capacity for structural and functional plasticity.

Acute changes in somatosensory evoked potentials following graded experimental spinal cord compression

Amplitude and latency of cortical somatosensory potentials evoked in cats by peripheral nerve stimulation were measured before, during, and for 5 hours after injury of spinal cord segment L-7 by a predetermined degree and duration of compression. An amplitude decrease, slight and transitory, was first observed after compression reduced the segmental cross section by 60%. After an 80% compression, amplitude reduction was initially larger and lasted longer, but recovered 2.5 hours after injury to a level that did not differ statistically from control values. After total (100%) compression, evoked responses disappeared abruptly and did not recover significantly. Latency was unaltered at all degrees of compression. Structural damage increased with the degree of compression. In this model, evoked potential changes neither reflect nor predict the magnitude of acute incomplete spinal cord injury.

Membrane conductance course during spike intervals and repetitive firing in cat spinal motoneurones

Summary The time course of membrane conductance was measured in gastrocnemius motoneurones of spinalised cats during (a) the afterhyperpolarisation (AHP) following a single antidromic spike, and (b) rhythmic firing, elicited by antidromic and intracellular stimulation. In a simple of 26 motoneurones, 18 (69%) showed a conductance decay during AHP which was not a simple exponential function of time. After an initial steep phase, conductance decline was markedly slowed down for a definite time (plateau phase). In the remaining 8 motoneurones (31%) conductance decay was nearly exponential. Relating the non-exponential conductance curve to the current-frequency relation (f-I curve) in the same cell a close correlation was found between the time to the end of the plateau phase and the time of interval shortening leading to the secondary range in the f-I curve. During repetitive firing evoked by antidromic stimulation the plateau phase was progressively smoothed out and conductance during successive AHPs summated. After the fifth spike, decay was exponential and summation reached a maximum. Conductances did not summate algebraically. Similar results were obtained during rhythmic firing evoked by intracellular stimulation. It is suggested that (1) divergence from a single repolarising conductance declining exponentially with time may be at least one of the factors involved in the shaping of the secondary range in the f-I curve, and (2) the progressive tendency to a simple exponential decline and non-algebraical summation of conductances during a short train of spikes contributes to adaptation.

Ultrastructural Characteristics of Glutamatergic and GABAergic Terminals in Cat Lamina IX Before and After Spinal Cord Injury

The present study was designed to: 1) morphologically characterize cat glutamate and GABAergic synaptic terminals in lamina IX in the intact spinal cord at the electron microscopic level using postembedding immunochemical techniques and .2), begin an analysis of how the synaptic architecture of glutamate and GABAergic terminals changes after an ipsilateral spinal cord hemisection. The present study shows that glutamate immunoreactive terminals are characterized by a wide synaptic cleft, asymmetric synaptic membrane densities and spherical synaptic vesicles. Most of the glutamatergic terminals are presynaptic to small or medium size dendrites. In contrast, GABAergic terminals display typical pleomorphic synaptic vesicles, a narrow synaptic cleft and a symmetrical membrane density. Qualitative analysis indicated that 13-17 months after hemisection, the length of the synaptic active zones in both glutamatergic and GABAergic terminals ipsilateral to hemisection is longer than those observed in the terminals contralateral to hemisection orfin normal control cats. Furthermore, the perimeters of both dendrites and either glutamate or GABA immunoreactive terminals are longer on the hemisected side compared with those observed in the nonhemisected side of the spinal cord. The results are important for complete understanding of the mechanisms which underlie locomotor recovery in mammals following spinal cord injury.

Accommodation of cat spinal motoneurones to linearly rising currents before and during long-term changes of membrane potential

Summary The rates of accommodation of slowly accommodating α-motoneurones of cats remain unchanged as long as the membrane potential (MP) remains constant. The rates increase during long-term artificially imposed MP depolarisation and decrease during hyperpolarisation. The decrease of the maximum rate of rise of the action potential (V ab ) with change in the action potential latency is greater during a depolarising and less during a hyperpolarising shift of the MP, as compared with the relationship found at the resting MP. The current-voltage curves are linear. Linearity is preserved and the slopes of the curves are unchanged during all MP displacements. The relationships betweenV ab and membrane potential before and during long-term changes in membrane potential are unchanged; they are not shifted along the potential axis. The results suggest that different states of the sodium-carrying system alone account for the dependence of rate of accommodation upon MP.

Regional Spinal Cord Blood Flow and Energy Metabolism in Rats after Laminectomy and Acute Compression Injury

Many data are available concerning spinal cord blood flow (SCBF) and metabolism on various models and timing after spinal cord injury, however, detailed information on their exact relationship in the same injury model is lacking. This relationship is a crucial factor in the understanding of the pathophysiology of spinal cord trauma.Rats were subjected to lumbar laminectomy or lumbar spinal cord compression trauma. 3 hours later, changes in SCBF were evaluated autoradiographically and changes in ATP, glucose and lactate levels were analyzed using substrate-specific bioluminescence techniques. Measurements were performed at the lesion site (segment L4), adjacent segments (L3 and L5) and at remote thoracic segments (Th8 to Th9).Laminectomy alone did not change SCBF, both in thoracic and lumbar segments. In contrast, ATP levels were significantly reduced and lactate levels were increased at the lesion site and in adjacent lumbar segments at 3 hours after laminectomy, whereas glucose levels were not significantly changed. In animal subjected to additional compression trauma, SCBF was significantly reduced in segments L3, L4 and L5 paralleled by a significant ATP reduction and lactate increase. Glucose levels did not differ significantly from controls 3 hours after compression injury. This metabolic profile was also reflected in the remote thoracic segments. In contrast, SCBF was not reduced in thoracic segments of traumatized animals.The observation that ATP was already significantly reduced and lactate increased in laminectomized segments and in remote thoracic regions after trauma signals that metabolic changes are sensitive indicators to spinal stress. The fact that posttraumatic metabolic profile differs from the pattern of hemodynamic and metabolic changes induced by ischemia, suggests posttraumatic mediators may be involved in the different regulation of the energy producing machinery.

Acute effects of dexamethasone on normal and on posttraumatic spinal cord polysynaptic reflex activity and axonal conduction

The effects of a single intravenous injection of a high dose of dexamethasone (4 mg/kg) on polysynaptic reflex activity and axonal conduction were measured for 5 hours in the intact and in the compression-injured L-7 spinal cord segment of high spinal cats. The segment was injured by a transient compression of preset degree and duration. In the uninjured preparation, dexamethasone administration significantly reduced polysynaptic reflex size for 2 hours. Axonal conduction was unaltered. One group of injured animals was given dexamethasone 30 minutes after trauma, whereas another was not treated. The acute posttraumatic changes in both parameters did not differ significantly in treated and untreated animals. Histopathologically, differences in the amount of segmental edema and hemorrhage between untreated and treated animals were not significant.

Increased functional vulnerability to acute compression injury of a spinal cord segment under barbiturate anesthesia

Posttraumatic changes in polysynaptic reflex activity and axonal long-tract conduction were measured after transient compression of the L-7 spinal cord segment of cats, either made high spinal and unanesthetized or left intact under pentobarbital anesthesia. The severity of acute post-injury changes increased significantly in the anesthetized animals. Partial recovery and stabilization of functional deficits were observed in the spinal cat, but not in the anesthetized one. These findings suggest that, at least in the acute postinjury stage, pentobarbital anesthesia may enhance functional damages after experimental spinal cord compression.