Can intubation harm the brain in critical care situations? A new simple technique may provide a method for controlling brain temperature.

Many animal species are able to keep the brain temperature some degrees centigrade lower than the deep body temperature when exposed to environmental heat stress. The lower temperature is based on cooling of the nasal venous blood through the respiratory airflow and local counter-current transfer of heat between venous and arterial blood in the cavernous sinus-carotid artery complex. Anaesthetized, intubated animals do not have any air flow through the nasal cavities. However, when the nasal cavities were flushed with oxygen, the deep brain temperature dropped within minutes and returned to previous values when the oxygen flushing was stopped. Cooling was found in animals with a rete mirabile (pigs), and in animals without a rete (rats). If a similar cooling mechanism is present in man (no rete) under intensive care, a simple flushing of the nasal cavities with gas will protect the brain against hyperthermal damage.

p75NGFR immunoreactivity in normal prenatal human dorsal root ganglia.

The purpose of the present study was to examine immunohistochemically the expression of the low-affinity p75 nerve growth factor receptor in the dorsal root ganglia from 12 human fetuses (gestational ages, 10-24 weeks) located in three different spinal segments (cervical, thoracic, and lumbosacral), using a monoclonal mouse-antihuman low-affinity p75 nerve growth factor receptor antibody. The low-affinity p75 nerve growth factor receptor immunoreactivity was present within the dorsal root ganglia and the surrounding nerve fibers in all spinal segments at the different gestational ages examined. From 10 weeks of gestation, three different types of neuronal staining were observed: dorsal root ganglia neurons without low-affinity p75 nerve growth factor receptor immunoreactivity (classified as type I neurons), neurons displaying weak low-affinity p75 nerve growth factor receptor immunoreactivity (classified as type II neurons), and neurons manifesting intense low-affinity p75 nerve growth factor receptor immunoreactivity (classified as type III neurons). The distribution of the three types of neurons in the dorsal root ganglia was identical in the three spinal segments and did not change between 10 and 24 weeks of gestation. This study provides the first demonstration of the low-affinity p75 nerve growth factor receptor immunoreactivity in the dorsal root ganglia from human fetuses at different gestational ages.

Prenatal localization of the dorsal root ganglion in different segments of the normal human vertebral column.

STUDY DESIGN: Vertebral columns from 11 normal human fetuses (10-24 weeks of gestation) derived from spontaneous abortions were examined as part of the legal autopsy procedure including spinal cord analysis. OBJECTIVES: To study the localization of the dorsal root ganglion in the normal fetal spine and to relate the dorsal root ganglion location to the ossification of the vertebral bodies and vertebral arches. SUMMARY OF BACKGROUND DATA: The normal and pathologic ossification pattern of the fetal human spine has been studied. There has been no study addressing the localization of the dorsal root ganglion in normal and pathologic axial development. METHODS: The dorsal root ganglion were studied by using histology (horizontal sections) and morphometric measurement. RESULTS: The study showed: 1) The dorsal root ganglion appeared before ossification of the spine; 2) The dorsal root ganglion had an oval shape in all cases; 3) The longitudinal axis of dorsal root ganglion was directed anterolaterally in the cervical and lumbosacral segments and mainly laterally in the thoracic segment; 4) During development, the dorsal root ganglion changed position according to the body axis; and 5) The para-axial ossification protected the dorsal root ganglion differently in the different axial segments. CONCLUSIONS: The dorsal root ganglion appeared before ossification. The distance from the dorsal root ganglion to the body axis increased during development. In the different segments of the spine, different orientations and different locations of the dorsal root ganglion were observed in relation to osseous spine components. The results can be used as reference data for future studies on the dorsal root ganglion in pathologic spines.

Rapid brain cooling in intubated pigs through nasal flushing with oxygen: prevention of brain hyperthermia.

Local cooling of the brain by the respiratory air is found in many animal species. The mechanism is based on cooling of the nasal vein blood and heat transfer in the cavernous sinus/carotid artery complex and is therefore not active in anaesthetised, intubated animals. The present experiment was made to investigate the effects of oxygen flushing of the nasal cavities in such animals. Nine anaesthetised, intubated male pigs were used. The temperatures in the third ventricle and rectum were measured continuously. Oxygen was infused into the nasal cavities during 10 min periods interrupted by 10 min without flow. The nasal oxygen flow constantly induced a rapid, reversible and flow dependant decrease in brain temperature: 0.25 degree C +/- 0.04, (n = 2) (mean +/- SD, n) at < 4 l/min; 1.35 degrees C +/- 0.78, (n = 20) at 4-6 l/min; and 1.44 degrees C +/- 0.62, (n = 6) at > 6 l/min. The ventricle temperature decreased 0.59 degree C +/- 0.23, (n = 8) when the animals were transferred to spontaneous respiration and the tracheal tube removed. It may be possible to protect the brain in intubated animals and humans from heat-induced damages by establishment of nasal flushing.

Cooling of the brain through oxygen flushing of the nasal cavities in intubated rats: an alternative model for treatment of brain injury.

Local cooling of the brain by respiration has been found in several animal species with a rete mirabile in the carotid artery/cavernous sinus complex. The present experiment was made to investigate whether a similar cooling could be found in the rat, which does not have a rete. Eleven rats were anesthetized and intubated. Three thermoprobes were inserted into the brain (two probes) and rectum, and the temperatures measured continuously. The nasal cavities were flushed with oxygen (250-1000 ml/min) during 15-min periods, interrupted by 15-min control periods. The mean brain temperature decreased by 0.43 +/- 0.03 degree C (n = 86, P < 0.005) with individual values up to 1.11 degrees C during the flushing periods. The decrease was oxygen-flow dependent, but not correlated to the rectal temperature. It is concluded that even an animal species without a rete mirabile is able to decrease the brain temperature through nasal cooling. The cooling was probably connected to the blood flow. If the results can be extrapolated to man (no rete mirabile), brain temperature can be decreased by nasal flushing with air or oxygen in intubated patients with hyperthermia. We also suggest that this simple treatment will reduce the infarct volume after head injury, trauma, or brain ischemia.

Lack of effect of short-term depletion of plasma complement C3 on the survival of syngeneic dopaminergic neurons following grafting into the intact rat striatum.

Metabolically compromised cells may be subject to complement-mediated cytotoxicity. The aim of this study was to clarify to what extent plasma complement C3 might contribute to the low survival (5-20%) of grafted dopaminergic neurons. The survival of intrastriatal cell suspension grafts of syngeneic dopaminergic, tyrosine hydroxylase (TH)-containing neurons was compared in rats subjected to short-term i.v. treatment with 1) cobra venom factor (CVF), or 2) placebo treatment. Depletion of plasma complement C3 by CVF was confirmed by crossed immunoelectrophoresis. With 159 +/- 37 (mean +/- SEM) TH-immunoreactive and 154 + /- 40 TH mRNA-expressing neurons in the CVF-treated rats (n = 9), and 117 +/- 34 TH-immunoreactive and 160 +/- 49 TH mRNA-expressing neurons in placebo rats (n = 6), the CVF treatment did not increase the survival of the grafted dopaminergic neurons. Similarly, CVF had no apparent effect on the astroglial, microglial, or oligodendroglial cell response within and around the graft. The data indicate that depletion of plasma complement C3 at the time of grafting has no effect on the long-term survival of syngeneic ventral mesencephalic dopaminergic neuronal grafts.