THE RELATIONSHIP BETWEEN NORADRENALINE TURNOVER IN CEREBRAL CORTEX AND ELECTRICAL SELF-STIMULATION THROUGH ELECTRODES IN THE REGION OF LOCUS COERULEUS

Role of locus coeruleus ?1-adrenoceptors in motor activity in rats

The question of whether or not the locus coeruleus (LC) participates in the control of motor activity has been controversial due to difficulties in demonstrating permanent motor deficits after neurotoxic lesions of this nucleus or of the dorsal noradrenergic bundle (DNB). In the present experiments it was shown in rats that acute local blockade (with terazosin) or stimulation (with phenylephrine) of LC alpha(1)-adrenoceptors respectively blocked or stimulated exploratory behavior in a novel cage and the home cage. Moreover, previous lesion of the DNB by i.p. DSP4 abolished the behavioral changes to local LC alpha(1)-receptor manipulation but did not affect motor activity in the novel or home cage by itself. These findings are consistent with the hypothesis that the intact LC does contribute to motor activity control, exerted in part by its alpha(1)-receptors; however, the permanent loss of this nucleus is compensated for by remaining CNS motor structures.

Amygdaloid kindling during wakefulness and paradoxical sleep in the cat. 1. Inhibitory influence of paradoxical sleep on kindling development

The development of amygdaloid kindling during wakefulness (W) and paradoxical sleep (PS) was compared in chronically implanted adult male cats. The animals were divided into 2 groups. One group was kindled during W (W-K) and the second during a burst of pontogeniculo-occipital (PGO) potentials during PS (PS-K). The threshold of amygdaloid afterdischarge (AD) was determined during W in the W-K group and during PS in the PS-K group. For the development of kindling, amygdala stimulation was applied daily. Results demonstrate that kindling development was markedly retarded in the PS-K group. From the first kindling trials, mean AD duration in the PS-K group was significantly shorter than in the W-K group and this difference was sustained until generalized convulsive seizures (GCSs) were reached by the W-K animals. Also, mean AD frequency in the PS-K group was significantly lower than in the W-K group. AD propagation to the contralateral amygdala and sensorimotor cortex was significantly retarded in the PS-K animals. Time spent in behavioral stages I and II of kindling was significantly longer in the PS-K animals than in W-K animals and the number of daily electrical stimuli required to reach the first GCS was significantly higher in group PS-K than in group W-K. It is concluded that PS exhibits an inhibitory influence over amygdaloid kindling development and this influence is mainly exerted during the early stages of epileptogenesis.

Amygdaloid kindling during rapid eye movement (REM) sleep in cats

Development of amygdaloid kindling was analyzed during REM sleep and during wakefulness. Daily evolution of electrographic and behavioral changes was significantly delayed in REM kindled rats. The number of kindling trials required to reach the first generalized convulsive seizure was also significantly increased in comparison with awake kindled animals. Changes in sleep organization were measured under REM kindling conditions. A significant increase in total sleep time and in the percentage of light slow-wave sleep was found during the kindling process. No significant sleep changes were observed in REM-established kindling. REM inhibitory influence over epileptogenesis is discussed.

Alterations in brain norepinephrine metabolism and behavior induced by environmental stimuli previously paired with inescapable shock

After exposure to a single session of inescapable footshock, rats show deficits in escape performance 24 h later when required to lever press on a fixed ratio (FR-3) schedule. Footshock stress produces an immediate increase in brain levels of 3-methoxy-4-hydroxyphenylglycol sulfate (MHPG-SO4), a major metabolite of norepinephrine in rat brain. Twenty-four hours after a single or repeated session(s) of footshock stress, when levels of MHPG-SO4 returned to baseline, increases in brain levels of MHPG-SO4, crouching and defecation behavior were elicited in rats by neutral environmental stimuli that had been previously paired with inescapable footshock stress. These results suggest that sensitization or conditioning of noradrenergic neuronal systems may be induced by environmental stimuli previously paired with stress, and may help to explain, at least in part, the deficits in escape performance observed 24 h after exposure to inescapable shock.

The locus coeruleus noradrenergic system--evidence against a role in attention, habituation, anxiety and motor activity

Lesions of the locus coeruleus system were induced by combined stereotaxic injections of 6-OH-dopamine to the ascending fibres and just lateral to the locus coeruleus itself, to deplete the noradrenaline content of both the cerebral and cerebellar cortices. A group of rats with cortical noradrenaline concentrations of less than 30 ng/g were compared with a group with lesser destruction of the system (mean noradrenaline concentration 71 +/- 44 ng/g) and with controls (mean noradrenaline 347 +/- 58 ng/g). Lesioned rats showed normal motor activity and exploration (assessed with a holeboard) and showed normal habituation of these behaviours. The lesioned rats gave no evidence of increased susceptibility to distracting auditory stimuli whilst licking for water, and the groups did not differ in their rate of habituation to these stimuli, or in dishabituation. In a social interaction test, lesioned animals showed a decrease in social contacts in an unfamiliar situation (interpreted as a response to anxiety) of similar magnitude to that seen in the control group. In this test, lesioned animals engaged in more 'aggressive' behaviour (boxing and wrestling) than did the controls. These findings are incompatible with hypotheses that the locus coeruleus system is an integral part of the physiological mechanisms which control gross motor behaviour, attention, habituation or anxiety. Together with previous findings with the benzodiazepines, the results with the social interaction test make it unlikely that the benzodiazepines exert their anxiolytic effects by inhibiting the locus coeruleus system.

Clinical Research Centre Division of Psychiatry 1974-1977

The Clinical Research Centre was established by the Medical Research Council as a major focus for patient-orientated research and as the clinical counterpart of the National Institute for Medical Research at Mill Hill which for 40 years has been the Council's largest establishment for basic research. In cooperation with the Department of Health and Social Security the Council embarked upon the Northwick Park project in which the Clinical Research Centre is closely integrated with a district general hospital – Northwick Park Hospital – built at the same time, and designed to serve the population of the Harrow Health District. Across each of the major specialties the Clinical Research Centre has Divisions with varying degrees of involvement in patient care. While there are 600 (District) beds allocated to local District needs, there are further 200 (National) beds which, in principle, are available for investigating and treating patients from outside the District admitted for research purposes. In practice, the extent to which research takes place on patients admitted for special investigations and, on the other hand, on patients admitted from the District as part of the service commitment, varies widely with specialty. In psychiatry it is predominantly the case that patients under investigation have been admitted from the District.

In vivo neurochemical analysis, by push-pull perfusion, of the mesocortical dopaminergic system of the rat during self-stimulation

The region immediately adjacent to a self-stimulation site in the medial prefrontal cortex of the unanesthetized rat was prelabeled with 0.5 mu Ci 14C-dopamine (DA) injected through an indwelling guide cannula. Then successive 5 min push-pull perfusions of the site with an artificial CSF were carried out at a rate of 25 microliter/min so that a washout curve of declining radioactivity was generated under control conditions. When square wave 100 Hz pulses were delivered to the contiguous self-stimulation site, the release of 14C-DA was enhanced either during the actual interval of electrical stimulation or in the perfusion sample collected immediately thereafter. In parallel experiments, however, self-stimulation by the rat of its ventral tegmental area failed to alter the kinetics of 14C-DA release from the cortex when homologous loci were perfused. Analyses by thin-layer chromatography of the perfusates for their content of catechol metabolities revealed that the homovanillic acid fraction declined during stimulation, whereas the level of DOPAC remained relatively elevated. Evidence was also obtained for the new synthesis and subsequent release of norepinephrine during the stimulation of the cortex of the rat. These results suggest that endogenous dopamine, because of the notable alterations in its release and metabolism, plays an important synaptic role in the mediation of self-stimulation behavior at the level of the cerebral cortex.