Hyperactivity, aphagia and motor disturbance following restricted lesions of midbrain in rats

Effects of d-amphetamine on arousal

This article is a review of studies conducted on the effects of amphetamine on behavior in animals by the late Walter Isaac and his associates. The principle findings and hypotheses developed over the 20 or more years of research are outlined and discussed. d-Amphetamine is thought to affect an organism's behavior by influencing the arousal level, mainly via the visual system.

Midbrain stimulation in the anesthetized rat: direct locomotor effects and modulation of locomotion produced by hypothalamic stimulation

The midbrain contains circuits that modulate locomotion. To delineate some of the involved regions, low-level stimulation (25 microA, 10 s train of 0.5 ms pulses at 50 Hz) was applied to the midbrain during locomotor stepping. Stepping was elicited in the anesthetized (pentobarbital, 40 mg/kg) rat by stimulating the hypothalamus with 0.5 ms pulses at 40 Hz at various currents. The rat was held in a stereotaxic apparatus such that locomotor stepping movements turned a wheel. Facilitation of locomotion was produced by stimulation in the anterior ventromedial midbrain and in the posterodorsal midbrain. When presented alone, such stimulation produced locomotion. Inhibition of locomotion was produced by stimulation of the superior colliculus (ventral layers) and the ventromedial midbrain. Additional inhibitory sites were found in the central gray and the lateral tegmentum. Inhibitory collicular stimulation, when presented alone, was characterized by the absence of any hindlimb response. Inhibitory ventromedial stimulation, when presented alone, frequently produced poststimulation locomotion and when presented with hypothalamic stimulation was characterized by postinhibitory increases in locomotion. These results indicate that: (1) the locomotor effects of stimulation in midbrain and hypothalamic sites can summate: (2) multiple locomotor suppressive systems are present in the midbrain and among them are a collicular system and a ventromedial system.

Involvement of the midbrain reticular formation in self-injurious behavior, stereotyped behavior, and analgesia induced by intranigral microinjection of muscimol

Bilateral microinjection of muscimol (60 ng), a gamma-aminobutyric acid (GABA) agonist, into the central region of the substantia nigra (pars reticulata) produced self-injurious behavior (SIB), stereotyped behavior and analgesic-like effects in rats. Bilateral electrolytic lesions of the midbrain reticular formation ventrolateral to the periaqueductal gray matter completely blocked the SIB but had little effect on stereotyped behavior produced by intranigral muscimol. Lesions of the midbrain reticular formation reduced the antinociceptive effect of intranigral muscimol on the tail-flick but not on the hot-plate test. Bilateral microinjection of muscimol (10-100 ng) into the midbrain reticular formation produced intense stereotyped behavior and had an analgesic-like effect on the hot-plate test but not on the tail-flick test. Stereotyped behavior appeared to interfere with the paw-lick response on the hot-plate test. These data suggest that the antinociceptive effect of intranigral muscimol on the tail-flick test is mediated by fibers that project to or pass through the midbrain reticular formation and that analgesia may play an important role in muscimol-induced SIB. The midbrain reticular formation does not appear to be involved in the stereotyped behavior produced by intranigral muscimol.

Electrolytic current parameters in the dorsolateral tegmental obesity syndrome in rats

Female rats received lesions in the dorsolateral tegmentum formed by the 20 sec passage of 0.25, 0.5, or 0.75 mA anodal or 0.5, 0.75, 1.0, 1.25, or 1.5 mA cathodal current. Although all lesion parameters induced roughly comparable body weight gains, the largest effect was seen with 1.25 mA cathodal current. Anodal lesions were much larger and induced transient periods of hyperactivity that confounded the effects of the lesions on body weight gain.

Feeding induced by injections of muscimol into the substantia nigra of rats: unaffected by haloperidol but abolished by large lesions of the superior colliculus

Intense activation of central dopamine systems has been associated with oral stereotyped behaviour, whereas less intense stimulation of these systems can increase feeding in non-deprived animals. There are several lines of evidence which suggest that the gamma-aminobutyric acid-containing striatonigral and nigrotectal projections are essential pathways mediating dopamine-related oral stereotypy. The present series of experiments was conducted to examine whether the same output route also mediates dopamine-related feeding. In the first experiment it was shown that bilateral injections of a sub-stereotypic dose of muscimol (0.05 nM) into the substantia nigra increased feeding of non-deprived rats. In Experiment II the feeding response was further characterised by demonstrating that food intake was initially suppressed for 30 min after which it was potentiated for 90 min. In Experiment III it was shown that a single dose of haloperidol (0.4 mg/kg), which was adequate to suppress overall food intake, was ineffective in preventing the increase in feeding produced by intranigral muscimol (0.05 nM). In contrast, it was demonstrated in Experiment IV that large lesions of the superior colliculus completely abolished the muscimol-induced increase in feeding. These results suggest that the striatonigral and nigrotectal projections may be important efferent pathways for both the oral stereotypy and the feeding responses linked with central dopamine transmission.

Reduced locomotor activity as an acute effect of damage to superior colliculus in rats

Rats with either electrolytic or radiofrequency lesions of the superior colliculus were tested in an open-field within 24 h of operation. They crossed significantly fewer squares and spent more time motionless then control animals, an effect that disappeared upon retesting 13 days later. Previously reported locomotor hyperactivity thus appears to be a chronic but not an acute effect of collicular damage in rats.

Dissociation of stimulation-bound feeding and apomorphine-induced gnawing by lesions of superior colliculus

The intense stereotyped gnawing induced by high doses of apomorphine is almost abolished by large bilateral lesions of the superior colliculus. It has been argued that the feeding produced by electrical stimulation of the lateral hypothalamic area is closely related to dopamine-mediated oral stereotypies; if so, it might be expected that lesions of the superior colliculus would also disrupt stimulation-bound feeding. Feeding was obtained from 14 hypothalamic electrodes in 8 hooded Lister rats. Subsequent electrolytic lesions of the superior colliculus had no overall effect on this behaviour from 13 of the 14 electrodes, even though the lesions reduced the gnawing induced by 8-20 mg/kg apomorphine to less than 10% of its preoperative intensity. It is concluded that stimulation-bound feeding and apomorphine-induced gnawing are not dependent on identical neural circuitry, and therefore stimulation-bound feeding is probably not mediated by the nigrotectal pathway.

Locomotor activity of rats in open field after microinjection of procaine into superior colliculus or underlying reticular formation

Whereas large lesions of the superior colliculus in rats increase locomotor activity in the open field, bilateral collicular microinjections of muscimol (an agonist of the inhibitory neurotransmitter GABA) have been reported to reduce open-field activity. This difference might be due to muscimol's acting on a subpopulation of collicular neurones, or to some feature of the microinjection technique. The issue was investigated by observing open-field behavior after reversible lesions produced by bilateral microinjections of the local anaesthetic procaine (10-300 micrograms in 0.5 microliter) into midbrain sites. Injections of procaine into the superior colliculus produced effects similar to those reported after muscimol injections: both locomotor activity and other exploratory responses were suppressed, with the rats spending much of their time motionless in an alert posture. In contrast, animals with injections of procaine into the mesencephalic reticular formation (MRF) ventral to the superior colliculus resembled rats given large collicular lesions: they showed very striking increases in locomotor activity, while their rearing and exploratory head movements were reduced. It is suggested that in some experiments large collicular lesions may have increased locomotor activity in the open field because they invaded underlying MRF. However, it is also possible that in rodents the acute effects of collicular inactivation, as assessed by microinjection of muscimol or procaine, are different from the chronic effects that are observed in experiments with electrolytic or radiofrequency lesions.