Cardiovascular parameters in a mixed-sex swine study of severe decompression sickness treated with the emulsified perfluorocarbon Oxycyte

Intravenous perfluorocarbons (PFC) have reduced the effects of decompression sickness (DCS) and improved mortality rates in animal models. However, concerns for the physiological effects of DCS combined with PFC therapy have not been examined in a balanced mixed-sex population. Thirty-two (16 male, 16 female) instrumented and sedated juvenile Yorkshire swine were exposed to 200 feet of seawater (fsw) for 31 min of hyperbaric air. Pulmonary artery pressure (PAP), cardiac output (CO), and systemic arterial pressure (SAP) were monitored before (control) and after exposure. Animals were randomized to treatment with Oxycyte (5 ml/kg; Oxygen Biotherapeutics, Inc., Morrisville, NC) vs. saline (control) with 100% oxygen administered upon DCS onset; animals were observed for 90 min. Parameters recorded and analyzed included PAP, CO, and SAP. In all animals PAP began to rise prior to cutis marmorata (CM) onset, the first sign of clinical DCS, generally peaking after CM onset. Female swine, compared with castrated males, had a more rapid onset of CM (7.30 vs. 11.46 min postsurfacing) and earlier onset to maximal PAP (6.41 vs. 9.69 min post-CM onset). Oxycyte therapy was associated with a sustained PAP elevation above controls in both sexes (33.41 vs. 25.78 mmHg). Significant pattern differences in PAP, CO, and SAP were noted between sexes and between therapeutic groups. There were no statistically significant differences in survival or paralysis between the PFC and control groups during the 48-h observation period. In conclusion, Oxycyte therapy for DCS is associated with a prolonged PAP increase in swine. These species and sex differences warrant further exploration.

Acclimation to decompression sickness in rats

Protection against decompression sickness (DCS) by acclimation to hyperbaric decompression has been hypothesized but never proven. We exposed rats to acclimation dives followed by a stressful "test" dive to determine whether acclimation occurred. Experiments were divided into two phases. Phase 1 rats were exposed to daily acclimation dives of hyperbaric air for 30 min followed by rapid decompression on one of the following regimens: 70 ft of seawater (fsw) for 9 days (L70), 70 fsw for 4 days (S70), 40 fsw for 9 days (L40), 40 fsw for 4 days (S40), or unpressurized sham exposure for 9 days (Control). On the day following the last exposure, all were subjected to a "test" dive (175 fsw, 60 min, rapid decompression). Both L70 and S70 rats had significantly lower incidences of DCS than Control rats (36% and 41% vs. 62%, respectively). DCS incidences for the other regimens were lower than in Control rats but without statistical significance. Phase 2 used the most protective regimen from phase 1 (L70); rats were exposed to L70 or a similar regimen with a less stressful staged decompression. Another group was exposed to a single acclimation dive (70 fsw/30 min) on the day before the test dive. We observed a nonsignificant trend for the rapidly decompressed L70 dives to be more protective than staged decompression dives (44% vs. 51% DCS incidence). The single acclimation dive regimen did not provide protection. We conclude that protection against DCS can be attained with acclimating exposures that do not themselves cause DCS. The deeper acclimation dive regimens (70 fsw) provided the most protection.

Effect of hyperbaric oxygen treatment on nitric oxide and oxygen free radicals in rat brain

Oxygen (O(2)) at high pressures acts as a neurotoxic agent leading to convulsions. The mechanism of this neurotoxicity is not known; however, oxygen free radicals and nitric oxide (NO) have been suggested as contributors. This study was designed to follow the formation of oxygen free radicals and NO in the rat brain under hyperbaric oxygen (HBO) conditions using in vivo microdialysis. Male Sprague-Dawley rats were exposed to 100% O(2) at a pressure of 3 atm absolute for 2 h. The formation of 2,3-dihydroxybenzoic acid (2, 3-DHBA) as a result of perfusing sodium salicylate was followed as an indicator for the formation of hydroxyl radicals. 2,3-DHBA levels in hippocampal and striatal dialysates of animals exposed to HBO conditions were not significantly different from controls. However, rats treated under the same conditions showed a six- and fourfold increase in nitrite/nitrate, break down products of NO decomposition, in hippocampal and striatal dialysates, respectively. This increase was completely blocked by the nitric oxide synthase (NOS) inhibitor L-nitroarginine methyl ester (L-NAME). Using neuronal NOS, we determined the NOS O(2) K(m) to be 158 +/- 28 (SD) mmHg, a value which suggests that production of NO by NOS would increase approximately four- to fivefold under hyperbaric O(2) conditions, closely matching the measured increase in vivo. The increase in NO levels may be partially responsible for some of the detrimental effects of HBO conditions.

Decompression sickness presenting as forearm swelling and peripheral neuropathy: a case report

Neurological symptoms after decompression from a dive are usually thought to be manifestations of central nervous system (CNS) decompression sickness (DCS). We present a case of DCS in which neurological symptoms are present but which the clinical findings, magnetic resonance imaging and electroneuromyographic studies suggest were caused by muscle injury and exacerbation of an existing peripheral neuropathy. This finding supports the alternative hypothesis that some neurological symptoms and signs in DCS are due to effects on peripheral nerves rather than the CNS.

Dexamethasone protection against photochemical retinal injury

Photochemical retinal injury was produced in the foveomacula of the rhesus monkey using the light from an indirect ophthalmoscope. The eyes were examined by both light and electron microscopy. Damage consisted of vacuolization of the retinal pigment epithelium and neurosensory retinal layers. Pretreatment with subcutaneous injection of dexamethasone for 16 weeks prior to light exposure markedly decreased damage to the retinal pigment epithelium, but had no apparent effect on damage to the neurosensory retina in eyes examined 18 hours after exposure. The mechanism responsible for this protective effect is unknown.

Choroidal blood flow. III. Reflexive control in human eyes

Choroidal blood flow helps maintain a stable temperature environment for the outer retinal layers, especially in the macular area. Recent studies in monkeys have demonstrated a centrally mediated reflexive mechanism that increases choroidal blood flow in response to light or light-generated heat. This increase in choroidal blood flow can be detected as an elevation in ocular surface temperature. With the use of ocular surface temperature as a semiquantitative index of alterations in choroidal blood flow, the existence of a similar reflex was demonstrated in normal human volunteers.

Observations on monkey eyes exposed to light from an operating microscope

Two cynomolgous monkeys were exposed to the light of an operating microscope. One eye was exposed to the light with the blue end of the spectrum filtered, while the other was exposed to unfiltered light. Neither group of eyes showed ophthalmoscopic evidence of a discrete retinal lesion. The eyes exposed to unfiltered light, however, showed histologic evidence of foveomacular change. The eyes exposed to filtered light showed lesser changes.

Apparent discrepancy between single-unit activity and [14C]deoxyglucose labeling in optic tectum of the rattlesnake

Autoradiographic analysis of [1-14C]2-deoxy-D-glucose-6-phosphate ([14C]2-DG-P) accumulation in the rattlesnake brain stem and optic tectum was used in an effort to map infrared and visual neuronal pathways. Visual stimulation with a standard stimulus (a heat lamp) resulted in dense labeling of the superficial layers of the optic tectum. Infrared stimulation with the same standard stimulus resulted in labeling at the first synaptic relay, the lateral descending nucleus of the trigeminal tract (LDN-V), but not at higher levels, including the optic tectum. Systematic comparison of electrophysiological properties of tectal neurons was performed using the standard stimulus. Responses of infrared units in one hemitectum and visual units in the other, elicited by the same stimulus used in the [14C]2-DG-P experiments, were analyzed. There were no clear differences in the number, maximal density, spread, or rates of accommodation of visual units and infrared units, although the locus of maximal density was more superficial for visual units. In general, infrared units generated a greater number of action potentials than did visual units. All infrared units responded only to onset of the stimulus but they varied greatly in their ability to maintain discharge for the full duration of the stimulus. Most visual units exhibited on-, off-, or on-off responses. Four units showed only inhibition of spontaneous activity during the visual stimulation. There were significant differences in the evoked responses elicited by visual and infrared stimulation in response to the standard stimulus. Infrared stimuli generated single, large, triphasic on-responses, whereas visual stimulation generated complex multiphasic and long-lasting on- and off-responses. The major infrared on peak reached maximal amplitude at greater depths and was larger than the major visual on peak. Amplitude of the infrared peak fell off more rapidly with distance from the locus of its maximum than did amplitude of the visual peak. These observations are consistent with the view that infrared stimulation is effective in discharging neurons but is not associated with intense synaptic excitation. In contrast, visual stimulation apparently does produce intense synaptic activity, as suggested by the duration, complexity, and spread of the visual evoked response. Failure of this synaptic activity to produce more spikes in visual units probably reflects either depolarizing spike inactivation or the admixture of excitatory and inhibitory actions. Our observations suggest that 2-deoxy-D-glucose uptake is not necessarily correlated with the degree of action potential activation of specific neuronal pathways. The amount of [14C]2-DG-P labeling may reflect the metabolic requirements for support of synaptic depolarization as well as that supporting action potentials.

Pharmacologic sensitivity of amino acid responses and synaptic activation of in vitro prepyriform neurons

1. In an effort to identify the neurotransmitter released from terminals of the lateral olfactory tract (LOT) we have studied excitatory amino acid agonist and antagonist actions on population and single-unit responses in submerged and perfused slices of rat prepyriform cortex. Previous studies suggest that the transmitter at this synapse is either aspartate (Asp) or glutamate (Glu). 2. The field potential reflecting the monosynaptic activation of pyramidal neurons after stimulation of the LOT was reversibly depressed by bath perfusion of agonists, with an order of potency being kainic acid (KA) greater than N-methyl-DL-aspartate (NMDA) greater than homocysteic acid (HC) greater than Asp = Glu. 3. The synaptic field potential was essentially unaffected by DL-alpha-aminoadipic acid (AA), 2-amino-3-phosphonopropionic acid (APP), and DL-alpha-diaminopimelic acid (DAPA), all presumed to be selective for Asp receptors, and by L-glutamic acid diethyl ester (GDEE), presumed to be specific for Glu receptors. The field potential was depressed or abolished by 2-amino-4-phosphonobutyric acid (APB), an agent known to block Glu responses in insect muscle. 4. The effects of ionophoretic application of agonists were studied on single neurons recorded extracellularly. While there was some variability among neurons in relative agonist potency, all neurons were excited by the five agonists with relative potencies in general similar to those observed for the field potentials. 5. Responses to Glu and Asp were unaffected by AA, GDEE, and APB at concentrations up to 5 X 10(-3) M. Responses to KA, NMDA, and HC were often depressed by APB but were unaffected by the other antagonists. The excitation on stimulation of the LOT was consistently, rapidly, and reversibly blocked by APB. 6. These observations are not consistent with either Glu or Asp being the neurotransmitter of the LOT.

Choroidal blood flow II. Reflexive control in the monkey

Temperature measurements were taken from (1) the retina-choroid in the macula, (2) the scleral surface, or (3) the bulbar conjunctiva of the cynomolgus monkey, while the fellow eye was exposed to a moderate-intensity light source. Light stimulation produced an increase in tissue temperature in the non-light-stimulated eye. The increase in tissue temperature presumably results from a reflexive increase in choroidal blood flow. Hydrogen washout measurements of blood flow in the retina-choroid confirmed this increase in flow. This active mechanism, along with the passive ability of the choroidal circulation to dissipate light-generated heat, may be an important physiologic safeguard in helping to maintain a stable temperature environment for the outer retinal layers in the macula.

Choroidal blood flow. I. Ocular tissue temperature as a measure of flow

Temperature measurements were taken from the retina-choroid, scleral surface, or bulbar conjunctiva in cats and monkeys. Decreasing choroidal blood flow by elevating intraocular pressure produced a decrease in ocular tissue temperature. Confirmation of choroidal blood flow changes was obtained by the hydrogen washout technique, an independent measure of blood flow. We conclude that ocular tissue temperature can be used as a semiquantitative index of choroidal blood flow, and, being noninvasive, has potential clinical application.

The stabilizing effect of the choroidal circulation on the temperature environment of the macula

A major physiologic function for the high-flow choroidal circulation is the stabilization of the temperature environment of the retina. This is especially important in the macular region, which lies at the focal point of the eye's optical system. Observations of temperature changes in the macula under varying conditions of ambient illumination and choroidal blood flow have established that the choroidal circulation serves a dual purpose in stabilizing retinal tissue temperature, acting both as a heat source and a heat sink, depending on prevailing tissue temperatures.

Fine structure and organization of the infrared receptor relay, the lateral descending nucleus of the trigeminal nerve in pit vipers

The morphology of the nucleus of the lateral descending tract of V has been studied in species of two genera of pit vipers, cottonmouth moccasin (Agkistrodon piscivorus piscivorus), and rattlesnake (Crotalus ruber and Crotalus horridus horridus). The nucleus is the site of termination of primary afferent neurons forming the infrared receptors in the facial pits. It is located on the external surface of the common descending tract of V and contains somata that range in size from 7 to 22 micrometer in A. p. piscivorus and 7 to 27 micrometer in C. ruber. Electron microscopy reveals that the lateral descending tract contains both A delta and C fibers. Degeneration experiments indicate that the A delta fibers are primary afferents. The source of the C fibers is unknown. The lateral descending nucleus in both the cottonmouth and rattlesnake is fundamentally similar in organization. Afferent terminals containing clear spherical vesicles make synaptic contact with dendritis processes within the main neuropil. These axon terminals are also postsynaptic to boutons containing pleomorphic vesicles and some large dense-core vesicles. The C fibers terminate in a neuropil at the margin of the lateral descending tract on small dendritic processes that appear to come from neurons within the nucleus. This neuropil is found external to the tract in the cottonmouth and internal to the tract in the rattlesnake. The terminals contain clear spherical vesicles and large dense-core vesicles. The singularity of input to this nucleus is apparently reflected in the morphology. This is discussed in relation to the subnucleus caudalis of the mammalian brainstem.

Lateral olfactory tract transmitter: glutamate, aspartate, or neither?

Aspartate and glutamate are the principal candidates for the excitatory neurotransmitter released by the lateral olfactory tract (LOT) in prepyriform cortex of the rat. Identity of action of the natural transmitter with exogenous glutamate and/or aspartate, however, has not yet been demonstrated. We show that bath-applied 2-amino-4-phosphonobutyric acid, a presumed specific glutamate antagonist, blocks LOT-stimulated prepyriform field potentials and single unit activity but not the single unit response to ionophoretically applied glutamate or aspartate in rat olfactory cortex slices. These results suggest that neither aspartate nor glutamate is the LOT transmitter. Responses to ionophoretically applied N-methyl-DL-aspartate, kainic acid, and DL-homocysteate were clearly decreased by 2-amino-4-phosphonobutyric acid. This suggests that these agents, usually presumed to be aspartate or glutamate agonists, act at different receptors than aspartate and glutamate.

Thyrotropin-releasing hormone has multiple actions in cortex

The responses to application of TRH were examined on 38 identified neurons in sensory motor cortex of cat. Two pyramidal tract (PT) and 3 nonpyramidal tract (NPT) neurons were directly excited by TRH. Two other NPT neurons were inhibited by TRH. TRH potentiated the excitatory action of ACh on 4 of 12 PT neurons and 1 of 2 unidentified cells. None of these neurons showed a direct effect of TRH. TRH did not potentiate the response to Glu on 12 cells tested, even when the same cell showed TRH modulation of the ACh response. None of the NPT cells examined showed TRH modulation of the excitatory ACh response. These results demonstrate that TRH has multiple actions in mammalian cerebral cortex, but that these actions, such as the modulation of the ACh responses, appear to exist on discrete populations of neurons.

A head holder and stereotaxic device for the rattlesnake

We describe an apparatus for immobilization of the rattlesnake head for brain experimentation. Its design also allows its use as a stereotaxic instrument for electrophysiological studies employing microelectrodes. Attachment of the head is at the two orbital ridges and the hard palate. The bregma provides a zero reference for the frontal, lateral, and depth coordinates.