Electrocortical changes induced by the perfusion of noradrenaline, acetylcholine and their antagonists directly into the dorsal raphé nucleus of the cat

Functional neuroanatomy of the noradrenergic locus coeruleus: its roles in the regulation of arousal and autonomic function part I: principles of functional organisation

The locus coeruleus (LC) is the major noradrenergic nucleus of the brain, giving rise to fibres innervating extensive areas throughout the neuraxis. Recent advances in neuroscience have resulted in the unravelling of the neuronal circuits controlling a number of physiological functions in which the LC plays a central role. Two such functions are the regulation of arousal and autonomic activity, which are inseparably linked largely via the involvement of the LC. The LC is a major wakefulness-promoting nucleus, resulting from dense excitatory projections to the majority of the cerebral cortex, cholinergic neurones of the basal forebrain, cortically-projecting neurones of the thalamus, serotoninergic neurones of the dorsal raphe and cholinergic neurones of the pedunculopontine and laterodorsal tegmental nucleus, and substantial inhibitory projections to sleep-promoting GABAergic neurones of the basal forebrain and ventrolateral preoptic area. Activation of the LC thus results in the enhancement of alertness through the innervation of these varied nuclei. The importance of the LC in controlling autonomic function results from both direct projections to the spinal cord and projections to autonomic nuclei including the dorsal motor nucleus of the vagus, the nucleus ambiguus, the rostroventrolateral medulla, the Edinger-Westphal nucleus, the caudal raphe, the salivatory nuclei, the paraventricular nucleus, and the amygdala. LC activation produces an increase in sympathetic activity and a decrease in parasympathetic activity via these projections. Alterations in LC activity therefore result in complex patterns of neuronal activity throughout the brain, observed as changes in measures of arousal and autonomic function.

Dorsal raphe vs. median raphe serotonergic antagonism. Anatomical, physiological, behavioral, neuroendocrinological, neuropharmacological and clinical evidences: relevance for neuropharmacological therapy

Monoaminergic neurons located in the central nervous system (CNS) are organized into complex circuits which include noradrenergic (NA), adrenergic (Ad), dopaminergic (DA), serotonergic (5-HT), histaminergic (H), GABA-ergic and glutamatergic systems. Most of these circuits are composed of more than one and often several types of the above neurons. Such physiologically flexible circuits respond appropriately to both external and internal stimuli which, if not modulated adequately, can trigger pathophysiologic responses. A great deal of research has been devoted to mapping the multiple functions of the CNS circuitry, thereby forming the basis for effective neuropharmacological therapeutic approaches. Such lineal strategies that seek to normalize complex and mixed physiological disorders, however, meet only partial therapeutic success and are often followed by undesirable side effects and/or total failure. In light of these, we have worked to develop possible models of CNS circuitry that are less affected by physiological interaction using the models to design more effective therapeutic approaches. In the present review, we cite and present evidence supporting the dorsal raphe versus median raphe serotonergic circuitry as one model of a reliable paradigm, necessary to the clear understanding and therapy of many psychiatric and even non-psychiatric disturbances.

The effects of a single dose and prolonged benzene administration on 5-hydroxytryptamine and 5-hydroxyindolacetic acid content in rat brain

The contents of serotonin (5-HT) and its major metabolite, 5-hydroxyindolacetic acid (5-HIAA), in the hypothalamus, the striatum and the remainder of the brain, after a single dose and prolonged administration of benzene were studied in rats. Benzene was injected s.c. in doses of 1/20-1/5 LD50 for single administration and in doses of 1/80-1/20 LD50 daily six days a week during four weeks of prolonged administration. Single administration produced a decrease in the 5-HT content of the hypothalamus and striatum, accompanied by an increase of the 5-HIAA level in the striatum. The highest contents of both 5-HT and 5-HIAA in the hypothalamus and the striatum were seen 45 min after benzene injection and lasted for at least 180 min. After prolonged benzene administration increases of both 5-HT and 5-HIAA contents were observed, particularly with striatum. The accelerated 5-HT turnover in rat brain after acute and prolonged administration of benzene indicates an effect of the hydrocarbon on the metabolism of 5-HT.

Interaction between noradrenergic and serotonergic brain systems as evidenced by behavioral and biochemical effects of microinjections of adrenergic agonists and antagonists into the median raphe nucleus

The effects of microinjections of adrenergic receptors agonists and antagonists into the median raphe nucleus (MR) on behavior and serotonin (5HT) metabolism was examined in rats. Administration of adrenergic alpha 1 and alpha 2 receptor agonists (noradrenaline, phenylephrine, clonidine) produced behavioral excitation in the open field test and a tendency to decrease the forebrain 5-hydroxyindolo-acetic acid (5HIAA) concentration. Opposite effects were seen after microinjection of adrenergic alpha receptor antagonists (phenoxybenzamine, phentolamine but not yohimbine). A significant negative correlation was found between the effects on locomotor activity and 5HIAA levels in these rats. No effect was present after injection of beta receptor agonist salbutamol or antagonist propranolol. It is suggested that noradrenaline released from noradrenergic terminals in the MR tonically inhibits the activity of 5HT neurons thus producing symptoms of 5HT deficiency and that this action of noradrenaline is probably limited to the effects on alpha 1 but not alpha 2 nor beta adrenoceptors in this brain region.

Further evidence for a correlation between EEG synchronization and plasma DBH activity in normal subjects

In a former investigation we had got evidence for a relationship between synchronization of the resting EEG and plasma dopamine-beta-hydroxylase (DBH) activity in healthy males. In order to substantiate this finding we now examined a new sample of males and a sample of females, both with either low-voltage or monotonous alpha-EEGs, and relatives of probands with either EEG type. In the new sample of males, the carriers of a low-voltage EEG (n = 15) again had significantly lower plasma DBH activity than the subjects with a monotonous alpha-EEG (n = 16). In females there was no difference. In the families of probands with a monotonous alpha-EEG the relatives carrying the trait significantly exceeded non-trait-carriers in DBH activity. This effect is mainly due to the male subjects, confirming the results in the proband groups. Presumably there are common genetic factors that contribute to the variability of both the EEG and DBH.--Taking into account experimental findings on central catecholaminergic activity and EEG synchronization, a hypothesis on the mechanisms that are responsible for the relationship is proposed.

Influence of electrical stimulation of the substantia nigra on spontaneous activity of raphe neurons in the anesthetized rat

Recent studies of afferent connections of the anterior raphe using the horseradish peroxidase technique have demonstrated a major projection originating in the substantia nigra (SN). The present acute electrophysiological study examined the influence of stimulation of the afferent on the activity of individual neurons in the raphe of the posterior midbrain and anterior pons (n = 51), and of a control group of cells (n = 15) located 2 mm lateral to the raphe. The predominant effect of SN stimulation at 0.1-1.0 mA, 1 Hz or 10 Hz, was suppression of raphe activity, with 63% of the cells showing cessation of firing following SN pulses and only 8% showing excitation. The average duration of suppression was 200 msec at 1 Hz and 38 msec at 10 Hz. In contrast, 40% of the lateral cells were excited, with 27% of the cells showing suppression. The mean duration of total suppression of lateral cell firing was 61 and 17 msec at 1 and 10 Hz, respectively. The results from the raphe cells are consistent with recent reports of stimulation of other forebrain and brainstem afferents to the raphe in which suppression of raphe activity was the main effect.

Comparison of the electrocortical changes induced by (+)-amphetamine and chlorpromazine when perfused directly into the dorsal raphé nucleus of the cat

1 (+)-Amphetamine mimicked the intermittent and sustained electrocortical desynchronization produced by (-)-noradrenaline (NA) when perfused directly into the dorsal raphé nucleus of cat encéphale isolé preparations. 2 The effects of amphetamine or NA were abolished or significantly attenuated by prior application of (-)-propranolol. 3 The effect of amphetamine, but not that of NA, was blocked by prior applications of guanethidine or chlorpromazine (CPZ). 4 Desmethylimipramine (DMI) produced dose-related changes in electrocortical activity which were similar to those induced by NA when applied to the same sites within the dorsal raphé nucleus. 5 DMI potentiated the effects of both amphetamine and NA, but guanethidine only abolished the DMI-induced potentiation of the amphetamine response. 6 (-)-Propranolol, guanethidine and CPA produced a short period of electrocortical desynchronization at the beginning of the perfusion period before antagonism of the amphetamine response was apparent. 7 The results suggest that CPZ and amphetamine have an action within the dorsal raphé nucleus possibly related to noradrenergic terminals.