Effect of adrenocorticotrophic hormone on the activity of sterol ester hydrolase from rat brain

Adrenocorticotrophic hormone (ACTH) stimulates in vitro the hydrolysis of oleoylcholesterol by a sterol ester hydrolase from rat brain synaptosomes. The stimulatory effect involves an alkaline shift of the pH optimum of catalysis and culminates at pH 6 with a 15 to 20-fold increase in lipolytic rates. The effect requires trace amount of organic solvent in the substrate emulsion and is dependent on the NH₂-terminal sequence extending through the basic amino acid residues at positions 15–18. The hormonal stimulation is decreased when a lipid-depleted preparation is used as enzyme source, and fully restored upon addition of lecithin. The results raise the possibility that ACTH may have a neuro-hormonal role in brain via modulation of local lipolytic processes.     

Nitric oxide voltammetric measurements in the rat brain after gamma irradiation

The effects of a lethal gamma irradiation were investigated on cerebral NO-ergic system by using a voltammetric method in freely moving rats. It is reported that the cortical NO concentration increases right from the end of the radiation exposure (15 Gy) and reaches a maximal magnitude (+120%) 24 h later. A dose-effect relationship from 2 to 15 Gy for gamma-ray exposure has also been observed. The effects, obtained with either an NO synthase inhibitor nonselective for the different NO synthase isoforms or an NO synthase inhibitor selective for the constitutive isoform, suggest that the radiation-induced increase in NO is likely to be dependent on the inducible NO synthase isoform. Moreover, experiments performed under ex vivo conditions showed that the cortical mRNA level for Ca(++)-independent NO synthase, the brain NOS activity, and urinary nitrites/nitrates increased significantly 24 h after gamma-ray exposure. These results demonstrate that a supralethal whole-body irradiation alters the NO-ergic pathways. The increase in NO obtained under such conditions might constitute a good index of central nervous system radiosensitivity during the acute phase of the radiation syndrome.     

Effect of one-time and chronic low-intensity irradiation on cathepsin L activity in rat brain

The effect of the total single and chronic roentgen irradiation in the dose of 0.25 Gy on the rats to alteration dynamics in lysosomal cysteine cathepsin L [CE 3.4.22.15] level in different brain regions (cortex, cerebellum, middle brain, varolian, hippocampus, striatum) was studied as a result of 1, 12, 24, 120 and 168 hours of exposure. The data obtained displayed the opposite consequences of chronic effect of 0.01 Gy during 25 days if compare with the single irradiation by 0.25 Gy that led to the cathepsin L changes different in directivity and activity level in dependence on brain region and post-irradiation period.     

Effect of gamma irradiation on insulin receptor interaction in rat erythrocytes

An insulin receptor interaction has been studied in rat erythrocytes after whole-body gamma irradiation (1 Gy). Specific binding of insulin was found to increase 30 days following irradiation against the background of a decreased immunoreactive insulin concentration in the blood. A change in the postirradiation activity of insulin receptors is considered as a manifestation of the homeostatic mechanism of "up" regulation in exposed animals.     

Influence of age and gamma irradiation on the proliferative activity in regenerating rat liver.

The effect of aging (2-14 months) and total body irradiation (5.7 Gy of gamma radiation) on liver regeneration was investigated in rats 30 h after partial hepatectomy. Exposure of rats to irradiation 30 min before partial hepatectomy caused latent injury in the remaining liver cells. During the course of liver regeneration this became manifested as a delay in increasing the nucleic acid concentration and content and liver weight and, furthermore, as inhibition of the increase in the mitotic index and cellularity and pronounced increase in the frequency of chromosome aberrations in the postmetaphase. The pattern of age-related changes during liver regeneration was the same as that after irradiation, so that the differences between irradiated and nonirradiated animals became smaller with age.     

The measurement of gamma-glutamyl hydrolase (conjugase) activity in rat brain

An assay using the artificial substrate, 2,4-diamino-10-methyl-pteroylglutamyl-gamma-glutamate (MTX-G₁), was developed to measure gamma-glutamyl hydrolase (conjugase), which hydrolyzes folylpolyglutamates. This assay allows us to: 1) measure conjugase for the first time in rat brain and 2) measure conjugase in a reliable, sensitive and inexpensive manner. The MTX-binding assay results were compared to samples analyzed by HPLC and found to vary by only 13%. The artificial substrate, MTX-G₁, had a lower rate of hydrolysis than pteroylglutamyl-gamma-glutamate (Pte-G₂), 70.7±0.64 and 92.6±0.22 nmoles/hr/mg protein respectively. Conjugase was semi-purified 24 fold in H₂O and found to have a pH optimum of 5.0.     

Effects of chronic gamma irradiation on the activity of adenylate cyclase in rat lung tissue]

Different phase changes were observed in adenylate cyclase (AC) activity of pulmonary tissue plasma membranes under chronic gamma-irradiation of rats at a dose-rate of 12.9 cGy/day. Comparison of AC basal activity with the data reported earlier on changes in ornithine decarboxylase activity under similar radiation conditions showed unidirectional changes which indicated that cAMP-dependent processes were possibly involved in radiation modification of ornithine decarboxylase.     

Ontogenesis of enkephalin and humoral endorphin in the rat brain

Radioimmunoassay and column chromatography techniques were used to study the postnatal development of two different opioid ligands, humoral endorphin and enkephalin in the rat brain. Similar patterns were observed for both male and female animals during the period examined (from birth to the seventh week of life). Humoral endorphin content of the developing rat brain was found to increase in parallel to enkephalin, exhibiting a ‘lag’ period of 2 weeks. The most dramatic increase in opioid levels was detected during the third week of life; this stage was followed by a gradual change up to the adult levels.     

Dynamics of the pathomorphological changes in the rat brain in relation to the dose of gamma irradiation

Neurohistological, histochemical, electron-microscopic and biometric techniques were used to study the response of rat brain to irradiation within a wide range of doses. Nerve cells were shown to be highly radioresistant. At the same time, synapses and blood-brain barrier structures were highly radiosensitive. The pathomorphologic changes in different brain areas followed a dose-time function.     

Effect of gamma irradiation on immobilized trypsin

The effect of ionizing radiation of 0.05-10 Mrad on trypsin immobilized on dialdehyde cellulose was being studied. After irradiation the activity of native trypsin decreases by 25%, as compared with the initial, while the activity of immobilized trypsin remains constant. Before immobilization cellulose undergoes special pretreatment that leads to a decrease in the initial contamination. Some samples of modified cellulose were contaminated by staphylococcus culture (200,000 microbes per 0.2 g) and then exposed to irradiation of 0.05-0.4 Mrad. A distinct correlation between the irradiation dose (0.05-0.4 Mrad) and contamination of the object was registered.     

The effect of low doses of external gamma irradiation on the chromatin structure and activity of the histone-specific proteinases of rat brain cells]

Irradiation of rats with doses of 0.5 to 2 Gy was shown to cause dose-dependent changes in the sensitivity of brain cell chromatin to the effect of DNAase I that were manifested by the increased level of DNA hydrolysis and a high content of the chromatin soluble fractions. The chromatin structure was only partially restored 24 h after irradiation. Changes in the chromatin structure were accompanied by the increase in the histone-specific proteinase activity.     

Effect of benzodiazepines on 5'-nucleotidase activity in rat brain

Experiments on 330 rats were made to study the influence of benzodiazepines (diazepam, dormicum and phenazepam) on 5'-nucleotidase activity in brain homogenates. It was discovered that diazepam and dormicum in doses of 3 and 4 mg, phenazepam in doses of 3.75 and 5 mg per 200 g bw provoked a 16-20% reduction in 5'-nucleotidase activity. The maximal effect of diazepam (3 and 4 mg doses) was attained 1 h after intraperitoneal injection, that of dormicum (3 mg) 30 min and of phenazepam (5 mg) 1 h after intraperitoneal injection. It is assumed that benzodiazepines are involved in AMP metabolism.     

Comparison of synenkephalin and methionine enkephalin immunocytochemistry in rat brain

Immunocytochemistry using an antiserum to the C-terminal octapeptide of synenkephalin, proenkephalin(63–70), was performed throughout the rat brain and revealed numerous immunopositive fibers and some cell bodies. The morphology and distribution of synenkephalin immunoreactivity was extremely similar to that of a commercial methionine enkephalin (Met-ENK) antiserum. Colchicine pretreatment allowed the immunostaining of cell bodies not otherwise possible without pretreatment, but did not affect the distribution of immunoreactive fibers. Using 6 μm serial sections, we were able to colocalize synenkephalin and Met-ENK immunoreactivities in gigantocellular neurons of the medullary reticular formation. Preabsorption of the antiserum with [Tyr⁶³]proenkephalin(63–70) octapeptide (YEESHLLA) completely eliminated immunoreactivity in the rat brain, while preabsorption with all other peptides used had no detectable effect. We conclude that our antiserum to synenkephalin is specific for enkephalinergic cell bodies, fibers and terminals. The synenkephalin antiserum used in these studies may have advantages over other antisera utilized for immunocytochemical detection of proenkephalin gene expression.     

The effect of the aminopeptidase inhibitor bestatin on the enkephalin level in the rat brain

Met- and leu-enkephalin contents in midbrain (including hypothalamus) and striatum of rats were determined by radioimmunoassay after bestatin (racemate) injection (200 g, i.c.v.). It was found that bestatin administration influenced the midbrain met-enkephalin content, values and directions of the changes observed being dependent upon the time after the injection. The data obtained confirm the participation of aminopeptidase in enkephalin inactivation and present evidence for the possibility of regional variations of enkephalin catabolism pathways in the brain.     

Effect of chronic psychogenic stress exposure on enkephalin neuronal activity and expression in the rat hypothalamic paraventricular nucleus

This study tested the hypothesis that the activation pattern of enkephalinergic (ENKergic) neurons within the paraventricular nucleus of the hypothalamus (PVH) in response to psychogenic stress is identical whether in response to repeated exposure to the same stress (homotypic; immobilization) or to a novel stress (heterotypic; air jet puff). Rats were assigned to either acute or chronic immobilization stress paradigms (90 min/day for 1 or 10 days, respectively). The chronic group was then subjected to an additional 90-min session of either heterotypic or homotypic stress. A single 90-min stress session (immobilization or air jet) increased PVH-ENK heteronuclear (hn) RNA expression. In chronically stressed rats, exposure to an additional stress session (whether homotypic or heterotypic) continued to stimulate ENK hnRNA expression. Acute immobilization caused a marked increase in the numbers of Fos-immunoreactive and Fos-ENK double-labeled cells in the dorsal and ventral medial parvicellular, and lateral parvicellular subdivisions of the PVH. Chronic immobilization caused an attenuated Fos response ( approximately 66%) to subsequent immobilization. In contrast, chronic immobilization did not impair ENKergic neuron activation within the PVH following homotypic or heterotypic stress. These results indicate that within the PVH, chronic psychogenic stress markedly attenuates the Fos response, whereas ENKergic neurons resist habituation, principally within the ventral neuroendocrine portion of the nucleus. This suggests an increase in ENK effect during chronic stress exposure. Homotypic (immobilization) and heterotypic (air jet) psychogenic stressors produce similar responses, including Fos, ENK-Fos, and ENK hnRNA, within each subdivision of the PVH, suggesting similar processing for painless neurogenic stimuli.