Lack of effects of hypothermia on cerebral amino acid uptake in vivo

Role of serotonin, gamma-aminobutyric acid, and glutamate in the behavioral thermoregulation of female tilapia during the prespawning phase

The role of hypothalamic neurotransmitter systems in behavioral thermoregulation was investigated in the prespawning female tilapia, Oreochromis mossambicus. Intrahypothalamic microinjection with serotonin (5-HT, 3 microliters of 1.0 x 10(-6) M) resulted in a significant increase in the selected temperature. This effect was mimicked by the agonist of 5-HT1A, 1B, and 2C receptors, N-3-trifluoromethylphenyl piperazine. Intrahypothalamic microinjection of tilapia with gamma-aminobutyric acid (GABA) resulted in a biphasic effect of the temperature selection, whereas microinjection with muscimol, an agonist of GABAA receptor, had no effect on temperature selection. Both agonist and antagonist of glutamate (Glu), N-methyl-D-aspartate (NMDA), and MK-801 (1.0 x 10(-6) M), a noncompetitive blocker of NMDA receptor, significantly decreased the preferred temperature. These results indicate that the hypothalamic 5-HT, GABA, and Glu systems play a role in the temperature selection of prespawning female tilapia.

The effect of profound hypothermia on blood-brain barrier permeability during pentylenetetrazol-induced seizures

The changes in the permeability of the blood-brain barrier during pentylenetetrazol (PTZ)-induced seizures were investigated in normothermic and hypothermic rats. Six groups of rats were studied: (I) normothermic control; (II) hypothermic control; (III) normothermia plus PTZ (80 mg/kg); (IV) normothermia plus PTZ (160 mg/kg); (V) hypothermia plus PTZ (80 mg/kg); (VI) hypothermia plus PTZ (160 mg/kg). The rats were anesthetized with diethyl ether. In the hypothermic animals, colonic temperature was reduced to 20 +/- 1 degree C by submerging the animals in ice water. In normothermic animals, distinct Evans-blue leakage was observed in the occipital cortex, thalamus, hypothalamus, substantia nigra, corpus striatum, and medulla oblongata in both PTZ groups. However, hypothermic animals which received a high dose of PTZ showed the most severe blood-brain barrier breakdown. Mean levels of Evans blue in the brains of low-dose (80 mg/kg) PTZ-treated animals were 8.7 +/- 2.2 micrograms/g and 5.7 +/- 1.4 micrograms/g in the normothermic and hypothermic groups, respectively. This difference was significant (P < 0.01). The levels in the high dose (160 mg/kg) PTZ-treated animals were 10.2 +/- 3.5 micrograms/g and 15.9 +/- 3.6 micrograms/g in the normothermic and hypothermic groups, respectively (P < 0.02). In conclusion, deep hypothermia prevents the blood-brain barrier disruption induced by 80 mg/kg pentylenetetrazol and aggravates the increase in permeability after 160 mg/kg pentylenetetrazol.

Different effects of hypothermia on amino acid incorporation and on amino acid uptake in the brain in vivo

The temperature dependence of the incorporation of amino acids into cerebral proteins and that of the transport of amino acids through the blood-brain barrier were studied. We measured the protein synthesis rate in vivo over a wide temperature range (14 degrees C-38 degrees C) in male Sprague-Dawley rats using a flooding dose of labeled valine. There was a linear dependence of the protein synthesis rate on temperature. The temperature quotient expressed as per cent decrease per 1 degree C was somewhat lower at the lower temperatures, a decrease from 7.8% in the 37.7-32.5 degrees C range to 6.7% in the 25.5-14 degrees C range. The transport of the three amino acids phenylalanine, lysine, and alanine, representing three transport systems, through the blood-brain barrier showed no temperature dependence in vivo. The results show that in hypothermia cerebral metabolic rates are lowered to a great extent, while some aspects of metabolic transport are not affected.

In vivo rates of protein synthesis in brain, muscle, and liver of five vertebrate species

To compare cerebral protein metabolism rates in vivo, protein synthesis rates of three organs of five vertebrate species were measured after a single i.p. injection of a flooding dose of [1-14C]valine. In muscle, brain, and liver, the respective average protein synthesis rates, expressed as percent of total protein-bound valine replaced per hour, that is, percent synthesis per hour, in goldfish at 22 degrees C body temperature, were 0.07, 0.23, and 0.57%; in the bullfrog at 20 degrees C, 0.06, 0.18, and 0.55%; in the white Leghorn chicken at 39 degrees C, 0.24, 0.70, and 2.17%; and in the mouse at 38 degrees C, 0.22, 0.65, and 2.0%. In the Tokay lizard at different body temperatures, the synthesis rates were 0.04, 0.13, and 0.43% at 26 degrees C; 0.05, 0.20, and 0.63% at 32 degrees C; and 0.07, 0.27, and 0.81% at 38 degrees C. The results demonstrate differences in protein synthesis rates in organs of the various species examined. The differences among the species seem to be due, to a major extent, to differences in body temperature; rates in lizard are below those in other species at temperatures tried. Protein synthesis rates in brain in all species are almost three times lower than those in liver and almost three times higher than those in muscle.

Hibernators' brain: protein synthesis in the neocortex and the hippocampus

[3H]leucine incorporation into 16 electrophoretic protein fractions from the neocortex and the hippocampus and their relative content have been estimated in various physiological states of ground squirrels: in torpor, in 3 transition phases, in long-term wakefulness and a fortnight after forced arousal in winter. The changes are greater in the neocortex than in the hippocampus. Incorporation is not the same in naturally awake animals and forced awake animals.

The effect of amino acids on protein metabolism as measured in long-term experiments in immature brain explants

In a study of a system suitable for investigating long-term effects on brain protein metabolism, we measured amino-acid incorpration into isolated immature brain explants incubated under sterile conditions up to ten days. Measurements of changes in total proteins, total DNA, cell number during the experiments, and 14C-thymidine incorporation measurements indicated no significant net growth; new cell formation was below 5% in a 5-day period; therefore, amino-acid incorporation was mainly due to protein turnover. The rate of incorporation in our immature brain preparation was similar to that of the adult brain in vivo: by ten days about one-half of the tissue protein turned over. The label incorporated was released in subsequent incubations with cold amino acids. Such release occurred in all subcellular fractions examined. Incorporation was fairly stable; at temperatures below 30 degrees C it rapidly declined, but it was not affected when phenylalanine or the branched chain amino acids (leucine, isoleucine, valine) were elevated in the incubation medium. Brief exposure to low amino-acid media had no effect; longer exposure resulted in tissue damage. Our model system indicates that overall brain protein turnover is not sensitive to such variations in the level of most amino acids, which may occur under various conditions. Protein metabolism of the nervous system occurs at a high rate. A recent long-term labeling method (Lajtha, Latzkovits, and Toth, 1976) gave a best fit to incorporation curves by assuming two compartments for adult brain proteins, one of which (about 6%) has a half-life of 15 hr and the other (94%) has a half-life of ten days. The disappearance of protein-bound label with time under conditions in which all proteins were previously labeled indicated that most, possibly all, proteins in brain are in a dynamic state (Lajtha and Toth, 1966). Incorporation of amino acids was found in all proteins and structures that have been studied to date; myelin proteins previously thought less active are also metabolized at a significant rate (Sabri, Bone, and Davison, 1974; Lajtha, Toth, Fujimoto, and Agrawal, 1977). We have fairly extensive information available in addition to turnover studies about the mechanisms of protein synthesis in brain (Roberts, 1971); protein breakdown was also studied in some detail (Marks and Lajtha, 1971). In contrast to our knowledge about protein metabolism under physiological equilibrium conditions, our information about alterations during functional demands or pathological conditions is scanty. Although a significant amount of work has been reported, largely because of technical difficulties the results are difficult to interpret unequivocally. The present report represents our effort to address some of the obstacles: to develop a system in which influences on long-term incorporation can be studied...