Effect of the steroidal alkaloid buxaminol-E on blood pressure, acetylcholinesterase activity and (3H)quinuclidinyl benzilate binding in cerebral cortex.

Pharmacological properties of the steroidal alkaloid buxaminol-E isolated from Buxus sempervirens varietas bullata were studied in relation to the cholinergic nervous system. In anaesthetised cats buxaminol-E (1.25 mumol/kg) initially induced a small short-lasting increase in blood pressure followed by marked hypotension. Atropine (1.47 mumol/kg) inhibited the hypotensive effect almost completely and methylatropine (1.47 mumol/kg) partially. Buxaminol-E and the muscarinic agonists McN-A-343 and bethanechol inhibited the binding of the muscarinic antagonist (3H)quinuclidinyl benzilate in cat and rabbit cerebral cortex membranes in decreasing order of potency. In about 10-fold higher concentrations they also inhibited acetylcholinesterase activity in cat cerebral cortex in the same order of potency. The results suggest that the hypotensive effect of buxaminol-E could be due to both central and peripheral activation of muscarinic receptors, and to a lesser degree to inhibition of acetylcholinesterase activity.

Acetylcholinesterase and choline acetyltransferase activity in some hypothalamic nuclei under immobilization stress in rats.

Rats were subjected to acute immobilization (IMO) for 1 or 2 h and killed by decapitation. The hypothalamic supraoptic and paraventricular nuclei were isolated by dissection technique and the activity of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) was assayed. A period of 1 or 2 h of IMO resulted in a significant increase of AChE activity only in the supraoptic nucleus, while no change of ChAT activity occurred. Acute IMO of 1 or 2 h duration resulted in an increase of AChE activity in supraoptic nucleus.

Changes in acetylcholine content, release and muscarinic receptors in rat hippocampus under cold stress.

The aim was to study the mechanism of the previously established decrease in acetylcholine (ACh) concentration in the rat hippocampus under cold stress. Male rats were exposed for 14 days to cold (5 degrees C) or kept (controls) at room temperature (24 degrees C). Acetylcholine content, release and muscarinic receptor binding were investigated in the hippocampus. Cold exposure resulted in a decrease of ACh concentration in the dorsal hippocampus. Moreover, the potassium-evoked release of ACh from hippocampal slices was increased and an increase of maximal binding capacity of [3H] (-) quinuclidinyl benzilate in the dorsal hippocampus of cold exposed animals was also observed. Thus the decrease of hippocampal ACh concentration under cold exposure is probably due to its increased release. On balance then, our results demonstrate that cold stress in the rat induces significant activation of the hippocampal cholinergic system.

Diminished growth hormone secretion in blind males after L-dopa stimulation.

Growth hormone secretion after L-dopa administration (1000 mg p.o.) was investigated in young adult normal and blind volunteers. The average increment of plasma growth hormone after L-dopa stimulation in the blind was below the criterion for a positive response (less than 5 ng ml-1). The control volunteers showed normal response. After L-dopa stimulation there was a significantly diminished growth hormone response in the young adult blind compared to control volunteers.

Acetylcholine and its enzymes in some brain areas of the rat under stress.

A period of 1 or 24 h of cold stress (5 degrees C) resulted in a significant decrease of acetylcholine (ACh) concentration in the hypothalamus and hippocampus in rats. In the hippocampus the activity of the choline acetyltransferase (ChAT) was significantly increased after 24 h and that of acetylcholinesterase (AChE) after 1 and 24 h exposure to cold, whereas in the hypothalamus, AChE activity was found to be decreased, albeit only after 24 h exposure. Separate investigation of the dorsal and ventral hippocampus under 24 h of cold revealed that the ACh decreased in the dorsal hippocampus only, where no change in ChAT activity was observed. On the other hand, ACh showed no change in the ventral hippocampus where an increase of ChAT activity was found. Forced swimming for 20 min also induced a significant decrease of ACh in the hippocampus and cerebral cortex, along with a significant increase of choline concentration in the given regions. We conclude that under certain stress situations the cholinergic system in rat brain areas, mainly in the hippocampus and hypothalamus, is activated.

Acetylcholinesterase activity in several hypothalamic and brain stem nuclei after acute and chronic immobilization stress in rats.

Acute and repeated immobilization stress increased acetylcholinesterase (AChE) specific activity in the nucleus supraopticus and median eminence of the rat and this increase was still present 24 hours after the 7th or 45th day of immobilization. The increase of AChE activity in those nuclei was probably related to the neuronal activation of the hypothalamic-pituitary axis during stress conditions. Acute and repeated immobilization was not accompanied by the change of AChE activity in A1 area and locus coeruleus. 46 days of immobilization periods produced a significant increase of AChE specific activity in the raphae dorsalis nucleus only which returned to normal values 24 hours after the last day of immobilization.

[Acetylcholinesterase and choline acetyltransferase in the nervous system of rabbits predisposed to cardiovascular disorders under emotional stress]. / Atsetilkholinésteraza i kholinatsetiltransferaza v nervnoi sisteme krolikov, predraspolozhennykh k narusheniiu serdechno-sosudistykh funktsii pri émotsional'nom stresse.

A study was made of the activity of acetylcholinesterase (AChE), cholinacetyl transferase (CAT), butyril cholinesterase (BCE) and water-soluble proteins in the structures of the CNS and in the autonomous ganglia in rabbits predisposed to cardiovascular disorders under emotional stress. It was established that unlike resistant animals, in those predisposed to cardiovascular disorders, the CAT content in the periphornical area of the hypothalamus did not differ from the control, the content of water-soluble proteins in the CNS structures and the ganglia remained unchanged either as compared with the control. The authors assume that the data obtained confirm a previously advanced concept of the involvement of the cholinergic system of the periphornical area of the hypothalamus in the maintenance of the stability of cardiovascular functions by regulation of the water-salt metabolism.

[Acetylcholinesterase and choline acetyltransferase in the nervous system of rabbits resistant to emotional stress]. / Atsetilkholinesteraza i kholinatsetiltransferaza v nervnoi sisteme krolikov, ustoichivykh k émotsional'nomu stressu.

To study the role of acetylcholine metabolism system in the mechanisms responsible for animals' resistance to emotional stress, the activity of acetylcholinesterase (AChE), butyrylcholinesterase and cholinacetyltransferase (CAT) was evaluated in brain structures and autonomous vegetative nervous system of rabbits after experimental emotional stress. In the course of experiments, arterial pressure and heart rate were recorded. The rabbits whose cardiovascular functions appeared to be resistant showed an increase in the activity of AChE and CAT in the perifocal area of the hypothalamus. It is suggested that the involvement of the perifocal area of the hypothalamus in the formation of the mechanisms responsible for the resistance is linked with the effects on water-salt metabolism.

Circadian susceptibility rhythms to some organophosphate compounds in the rat.

LD50 values after i.p. doses of phenitrotion (PH), dichlorvos (D) and methyl parathion (MP) were established at 0600, 1200, 1800 and 0000 and plasma corticosterone was determined in male rats. The PH toxicity was significantly higher at 0600 than at 1800. Moreover, there was a significant difference between the PH toxicity at 1200 (lower) and 0000 (higher). The D toxicity differed significantly only between 1200 (higher). There was however a lack of circadian susceptibility, rhythm to MP. The results differ according to the metabolic fate and the solubility of the tested compounds.

Human circadian rhythms in continuous darkness: entrainment by social cues.

Three groups of two subjects each were kept in underground chambers, first for 4 days in an artificial light-dark cycle, and thereafter for 4 days in complete darkness. They lived on a rigorous time schedule. Physiological as well as psychological functions were measured at 3-hour intervals. There were no differences in the results between the two sections of the experiment. Social cues are sufficient to entrain human circadian rhythms, and absence of light has no immediate effect on the functions measured.