Mechanism of action of substance P

Effects of MET-ENK, substance P and SRIF on the behavior of Hemichromis bimaculatus

Administration of 10 and 30 micrograms methionine-enkephalin (MET-ENK)/g bw (n = 10/dose) affected the propensity towards fighting in H. bimaculatus; 10 micrograms increased, while 30 micrograms decreased the aggressive behavior. MET-ENK also affected a number of behavior patterns displayed by the fish. Moreover, the "wet-dog-shakes" observed suggest that MET-ENK acts on opiate-receptors. Treatment with substance P (SP)/g bw (n = 10/dose) induced chafing movements in the fish slightly. It also decreased fighting and increased biting of the air stone, which is evidence that H. bimaculatus is still aggressive, directing its attacks to different objects. When 4, 8, 12 micrograms somatostatin (SRIF)/g bw (n = 10/dose) were injected, H. bimaculatus stopped fighting for several hours after the onset of treatment, depending on the dosage. Somatostatin reduces blood glucose concentration, causing a sudden stop of aggressive behavior, 0.04, 0.1, 0.6, 1.0 and 3.0 IU prolactin (PRL)/g bw (n = 5/dose) eventually decreased fighting and affected a number of behavior patterns displayed by the fish.

Distortions of vision and pain: two functional facets of D-lysergic acid diethylamide

D-lysergic acid diethylamide (LSD) produces distortions of visual perception and analgesia. Evidence is advanced from a functional standpoint that the observed visual effects result from an attenuation of light-evoked input to the dorsal lateral geniculate nucleus (LGN) from the purely centripetal pathways of the retina. More slowly responding visual afferents or those with more complex receptive fields seem to be affected most. LSD analgesia, accompanied by severe psychotic symptoms, appears to result from drug actions on a centrifugally controlled pain system involving neurons of the midbrain raphe.

Effects of substance P injected into the substantia nigra

1 Behavioural and biochemical effects of substance P (SP, 1 to 10 mug) administered in a small volume to discrete areas of the rat's brain were studied by means of a refined microinjection technique.2 SP injected unilaterally into the zona reticulata of the substantia nigra elicited dose-dependent contraversive circling and an increase in dopamine turnover in the ipsilateral striatum. SP applied to the zona compacta or zona lateralis, or to the medial lemniscus, evoked ipsiversive turning with a fall in dopamine turnover and a rise in 5-hydroxytryptamine (5-HT) turnover in the corresponding striatum.3 In both cases the onset of turning was immediate, reached a peak at about 5 min and lasted for 10 min. Both types of behaviour were blocked by haloperidol and exaggerated by nialamide.4 Unilateral injections of SP given into the crus cerebri, zona incerta, caudate nucleus, putamen or globus pallidus did not modify the animal's behaviour.5 In rats pretreated with apomorphine or amphetamine, SP induced contraversive circling which was followed by locomotion in the opposite direction.6 Turning responses to a second dose of SP were diminished at 3 h and reproducible at 24 h after the first injection.7 Bacitracin (50 ng) injected into the zona reticulata caused ipsiversive turning. Larger intranigral doses of bacitracin (10 mug), as with intracisternal SP (10 mug), evoked ;barrel rotation'.8 No changes in the free concentrations of aspartate, glutamate, gamma-aminobutyric acid, glycine or alanine were detected in any brain region following an intracisternal injection of 10 mug SP, although glutamine levels were elevated throughout the brain 30 to 60 min later.

Brain glycine and aggressive behavior

Intraperitoneal glycine reduced aggressiveness caused by water deprivation or forebrain septal lesion in the rat. Nalorphine and mephenesin, drugs previously shown to elevate central glycine levels, acted in the same way as systemically administered glycine. In mice made aggressive by prolonged isolation, glycine and mephenesin acted as tranquilizers, but nalorphine failed to act. Aggressiveness in mice, induced by L-dopa or clonidine was enhanced by nalorphine and mephenesin, but was left unaffected by systemically administered glycine. Behavioral effects of glycine extend to other forms of excitation.

Stimulation of brain adenylate cyclase activity by the undecapeptide substance P and its modulation by the calcium ion

Synthetic substance P stimulated adenylate cyclase activity in particulate preparations from rat and human brain. The concentration of substance P for half maximal stimulation in rat brain was 1.8-10-minus 7 M. The stimulatory effect of substance P on the rat brain adenylate cyclase activity was 88% compared with 48% by noradrenalin, 163% by prostaglandin E1 and 184% by prostaglandin E2. Both the basal and substance P-stimulated adenylate cyclase activity in rat brain were inhibited by concentration of Ca-2+ above 10-minus 6 M. The chelating agent ethyleneglycol-bis-(beta-aminoethylether)-N, N'-tetraacetic acid at a concentration of 0.1 mM reduced the basal adenylate cyclase activity by 64% and eliminated the substance P-stimulated activity. The inhibition by ethyleneglycol-bis-(beta-aminoethylether)-N, N'-tetraacetic acid was completely reversed by increasing concentrations of Ca-2+.