[Decrease of ACh response in isolated duodenum from SART stressed (repeated cold stressed) mice (author's transl)]

Effects of continuous and intermittent cold (SART) stress on sympathoadrenal system activity in rats

We compared sympathoadrenal responses to intermittent cold (SART) stress (in which cold exposure is interrupted by 4-hourly intervals daily at room temperature) with those to continuous cold (-3 degrees C) stress. Plasma levels of dihydroxyphenylalanine (DOPA), catecholamines and their metabolites as well as tyrosine hydroxylase (TH) activities in sympathetically innervated tissues were examined in rats exposed to each stressor for 1 day or for 5 days. Neither SART nor continuous exposure to cold for 1 day or 5 days altered plasma epinephrine (EPI) levels. However, norepinephrine (NE) and dihydroxyphenylglycol (DHPG) levels increased markedly during exposure to these stressors. On the first day of SART or continuous cold stress, NE levels were increased similarly, but the increments in DHPG levels were greater during SART stress. Since DHPG is formed in neurons, neural reuptake of NE may be more enhanced on the first day of SART stress than on the first day of continuous cold stress. After 5 days of SART stress plasma NE levels were significantly higher than those found after 5 days of continuous cold exposure. Plasma levels of DHPG were elevated to the same extent in both 5 days SART- and continuously cold-stressed rats, whereas plasma levels of methoxyhydroxyphenylglycol (MHPG) increased only by 5 days SART stress. Even at 1 h after the removal from 5 days SART stress, increased plasma levels of NE, DHPG and MHPG were still evident. These results suggest that 5 days SART stress elevates extraneuronal O-methylation of DHPG, and that NE turnover is more greatly increased by SART stress than by continuous cold stress. Plasma levels of DOPA, dopamine, dihydroxyphenylacetic acid and homovanillic acid also increased after either SART or continuous cold stress for 1 day and 5 days. Adrenal TH activities were significantly increased in rats exposed to SART or continuous cold stress for 1 day and 5 days, but in brown fat TH activity was elevated only in rats exposed to 5 days of continuous cold. Both SART and continuous cold stress are selective and potent stimuli for activation of the sympathoneural system, apparently without significant adrenomedullary EPI release. The increase of TH activity in the brown fat pad as well as of plasma NE and its metabolites is probably a result of adaptation to cold. It appears that even short intervals of return to a normal environmental temperature, as in SART, are sufficient to diminish sympathetic adaptation to cold.

Changes in muscarinic acetylcholine receptors in the isolated duodenum from repeatedly cold-stressed rats and the effect of neurotropin

In rats repeatedly cold-stressed by specific alternation of rhythm in environmental temperature (SART-stressed rats), the contractile response to acetylcholine (ACh) of the isolated duodenum was remarkably decreased, whereas the contractile responses to K+, Ba2+ and Ca2+ were comparable to those in non-stressed rats. The amount of [3H]quinuclidinyl benzilate in the duodenum of SART-stressed rats was about 50% of that in non-stressed rats, but the KD value remained unchanged. Long-term administration of hexamethonium prevented the changes in SART-stressed rats. The daily treatment with Neurotropin, an extract isolated from inflamed rabbit dermis inoculated with vaccinia virus, dose-dependently prevented the changes in SART-stressed rats. However, Neurotropin had no effect on the ACh-induced decrease in muscarinic ACh receptor (m-ACh.R) in cultured vas deferens of guinea pig. These results suggest that down-regulation of m-ACh.R in duodenum by SART stress may be associated with enhanced activity in the parasympathetic center. Moreover, Neurotropin is thought to prevent the down-regulation of m-ACh.R throughout the central nervous system.

Action of neurotropin on rat hypothalamic neurons in tissue slices

To clarify some of the actions of Neurotropin (NSP), intra- and extracellular measurements were made of 140 paraventricular (PVN) and 48 ventromedial nucleus (VMH) neurons in rat hypothalamic tissue slices in vitro while perfusing NSP, an extract from the inflamed skin of rabbits inoculated with vaccinia virus, through the recording chamber. NSP mostly decreased activity in PVN neurons (inhibition, 46; excitation, 27; excitation-inhibition, 5; no response, 62), and mostly increased it in VMH neurons (excitation, 12; inhibition, 3; no response, 33). Inhibition of PVN neurons by NSP was due to hyperpolarization with no change in membrane conductance. Since ouabain antagonized the NSP-induced inhibition of PVN neurons, the effect was probably due to activation of the sodium pump. Activity of some NSP-responsive PVN neurons was increased by increase of extracellular osmolarity, and activity of some NSP-responsive VMH neurons was increased by glucose application. The results suggest central modulation of autonomic or neuroendocrinological function by distinct NSP influence on PVN and VMH neural activity.

Total acetylcholine content, and activities of choline acetyltransferase and acetylcholinesterase in brain and duodenum of SART-stressed (repeated cold-stressed) rat

The cholinergic activities in SART (specific alternation of rhythm in temperature)-stressed (repeated cold-stressed) rats, which are diseased rats with vagotonic-type dysautonomia, were examined with the following results. A decreased content of total acetylcholine (T-ACh) and increased activities of choline acetyltransferase (CAT) and acetylcholinesterase (ACh) in the basal ganglia and an increase in the T-ACh content and decrease in the AChE activity in the duodenum of SART-stressed rats reached the respective plateaus on day 5 of stress, which were maintained thereafter. CAT activity, however, in the hypothalamus was activated most on day 2. These changes in SART-stressed rats were different from those in simple cold-stressed rats. Subdiaphragmatic vagotomy inhibited the appearance of the changes in the duodenum, but not those in the hypothalamus of SART-stressed rats. The sedative analgesic Neurotropin prevented all the changes in SART-stressed rats described above. These results suggest that cholinergic neurons may be activated in both the hypothalamus and basal ganglia of the brain of SART-stressed rats, and the characteristic peripheral changes of the cholinergic system in the duodenum of SART-stressed rats may be under the control of the parasympathetic center.

Changes of tissue blood flow in mice loaded with SART (repeated cold) stress or restraint and water immersion stress and the effect of administered neurotropin

In order to explore the peripheral microcirculation and to obtain an outline of autonomic innervation in SART (specific alternation of rhythm in temperature)-stressed (repeated cold-stressed) animals, which are regarded as model animals for clinical vagotonic-type dysautonomia, peripheral tissue blood flow was determined in mice, using the hydrogen clearance method. SART-stressed mice showed a decrease in gastric blood flow, no change in hepatic blood flow and an increase in dermal blood flow. In the mice exposed to the restraint and water immersion stress (RWIS), a type of acute stress, in contrast with SART stress which is a subacute type, remarkable decreases were observed in gastric, hepatic and dermal blood flows. Changes of both gastric and dermal blood flow in SART-stressed mice were dose-dependently prevented and maintained within normal limits by the treatment with Neurotropin, a sedative analgesic which is an extract isolated from vaccinia virus-inoculated and inflamed skin of rabbits. In RWIS-loaded mice, Neurotropin exhibited a great preventive effect on changes of blood flow in the stomach, a slight effect in the liver, and no effect in the cutis. When mice were loaded with SART stress after left-cervical vagotomy, SART stress failed to elicit any decrease in gastric blood flow. In SART-stressed mice treated with 6-hydroxydopamine, gastric and dermal blood flows tended to show a further decrease and increase, respectively, over and above the changes caused by SART stress. From these results, it is suggested that SART-stressed mice may have decreased gastric parasympathetic tone, a decrease in sympathetic tone and also other anomalies such as increased tension of the sympathetic cholinergic vasodilator nerves in the cutis.