Role of central nervous system monoamines in cardiopulmonary effects of Althesin in rabbit and man

The steroid induction agent, Althesin, infused intravenously in light anesthetic doses in otherwise unsedated man (84 micrograms kg-1 min-1) and rabbit (140 micrograms kg-1 min-1) causes similar autonomic and somatic effects. In the rabbit, the rise in heart rate (mainly due to central vagal blockade) and the selective depressant effects on respiratory rate are independent of CNS 5-hydroxytryptamine and noradrenaline. The rise in arterial pressure and the fall in hindlimb conductance is dependent on CNS 5-hydroxytryptamine and noradrenaline synthesizing neurons, which are probably arranged in series. These findings provide a working hypothesis for the mechanisms of action of Althesin on central cardiopulmonary controls in man.

Neuromuscular response of the immature rat of ACTH/MSH 4--10

The adrenocorticotropin fragment ACTH/MSH 4--10 (0.1 ug/kg IP) effectively modulates the neuromuscular responses of 9 to 15 day old rats. Muscle (extensor digitorum longus) contraction amplitude is increased, fatigue is delayed and muscle half-relaxation time is shortened during 20 min of continuous in situ stimulation of a branch of the deep peroneal nerve (square wave shocks 10 Hz, duration 0.5 msec, strength supermaximal). No effect on contraction time is seen. There is no facilitation or change in any contraction parameter in rats older than two weeks (16 to 40 days) indicating that these older animals, like normal adult rats, are unaffected by the peptide. Immature rats, however, are even more sensitive than hypophysectomized adult rats [29] to the ameliorative action of ACTH/MSH 4-10. This early sensitivity to ACTH/MSH 4--10 corresponds to important developmental changes occurring in nerve and muscle during the most critical period in postnatal development, the first two weeks.

An effect of beta-melanocyte stimulating hormone (beta-MSH) on alpha-motoneurones of cat spinal cord

Actions of beta-MSH and of melatonin on the recovery cycle of single spinal neurones were studied in the decerebrate-spinal cat. beta-MSH facilitated the rate of post-excitation recovery of alpha-motoneurones and some internuncial neurones, and melatonin inhibited the rate of post-excitation recovery. These observations provide additional evidence that beta-MSH functions in the nervous system as a modulator, and may help explain actions of beta-MSH in modifying acquisition of conditioned avoidance responses as well as its interaction with drugs such as morphine.

Hormonal release of programmed behavior in silk moths: probable mediation by cyclic AMP

The eclosion hormone triggers a stereotyped preprogrammed pattern of behavior in silk moths. The effects of the hormone were duplicated by the injection of dibutyryl adenosine 3', 5'-monophosphate, adenosine 3', 5'-monophosphate (cyclic AMP), or guanosine 3', 5'-monophosphate (cyclic GMP) into theophylline-treated pharate moths. Treatment with theophylline reduced the latency of the response to a low dose of hormone, presumably by blocking phosphodiesterase. Endogenous levels of cyclic AMP, but not cyclic GMP, increased significantly in the central nervous system within 10 minutes after hormone injection. We conclude that an early step leading to the release of the eclosion motor program is an increase in cyclic AMP in target neurons of the central nervous system.

Peptide enhancement of neuromuscular function: animal and clinical studies

Evidence is presented for an extra-adrenal effect of ACTH and ACTH analogs on muscle action potentials (APs), contractions and fatigue in in situ experiments. ACTH, alphaMSH, betaMSH and ACTH 4-10 increase the amplitude of APs and contractions and decrease fatigue in intact, hypophysectomized and in adrenalectomized rats, subjected to repetitive indirect stimulation (supermaximal strength, 5/sec or 10/sec for 30 min). Elevation of endogenous ACTH resulting from adrenalectomy or cold stress, or both, has the same effect as ACTH administration. ACTH peptides are most effective in depressed physiological conditions e.g. following hypophysectomy. As the effect of ACTH 4-10 is abolished after section of the motor nerve, it is inferred that this peptide may affect central motor neurons. Preliminary observations from clinical studies with ACTH 4-10 in patients with muscle disease, in whom a pathological decline in amplitude of a short series of evoked muscle APs was prevented by peptide administration, also indicate a possible action of this peptide on central nervous system neurons.