Mauro Mancia

GABAergic and other noncholinergic basal forebrain neurons, together with cholinergic neurons, project to the mesocortex and isocortex in the rat.

The extrathalamic relay from the brainstem reticular formation to the cerebral cortex in the basal forebrain has been thought to be constituted predominantly, if not exclusively, by cholinergic neurons. In contrast, the septohippocampal projection has been shown to contain an important contingent of γ‐aminobutyric acid (GABA)ergic neurons. In the present study, we investigated whether GABAergic neurons also contribute to the projection from the basal forebrain to neocortical regions, including the mesocortex (limbic) and the isocortex in the rat. For this purpose, retrograde transport of cholera toxin (CT) was examined from the medial prefrontal cortex for the mesocortex and from the parietal cortex for the isocortex and was combined with dual‐immunohistochemical staining for either choline acetyltransferase (ChAT) or glutamic acid decarboxylase (GAD) in adjacent series of sections.

Electrophysiological and behavioural changes owing to splitting of the brain-stem in cats

Abstract 1. 1. A midline pontine split induced a persistent alteration of sleep-wakefulness rhythms in cats; sleep (synchronized and desynchronized) was drastically reduced, reaching mean percentages of 16.7% (synchronized sleep) and 4.4% (desynchronized sleep). Wakefulness remained persistently very high (78.9%). These changes lasted 3–5 weeks after the splitting procedure. Similar changes in sleep and wakefulness were observed after bilateral pontine splits at 3 mm from the midline, in which the pontine raphe nuclei were spared, and after unilateral longitudinal pontine section at 1.5–2 mm from the midline. 2. 2. A midline bulbar split did not cause any consistent change in the sleep-wakefulness cycle of the cat. A mesencephalic split significantly reduced the amount of desynchronized sleep whilst synchronized sleep was not modified. An apparent blindness was observed in this preparation. 3. 3. Marked alterations in behaviour, such as restlessness and hyperirritability, together with a marked loss of body weight, were observed in cats with severe sleep deprivation induced by pontine splitting. 4. 4. The retrograde changes in the aspecific brain-stem neurones brought about by midline and bilateral pontine splits suggest the hypothesis that the persistent increase in wakefulness and reduction of sleep (synchronized and desynchronized), induced by these cuts, may be ascribed to suppression or reduction of the flow of physiological sleep impulses (synchronizing and desynchronizing the EEG) originating in regions at the level of the pontine section or caudally to them, and ascending contralaterally to diencephalic and cortical regions.

Changes in the serotonergic system during the sleep-wake cycle: Simultaneous polygraphic and voltammetric recordings in hypothalamus using a telemetry system

Changes in the serotonergic system in the posterior hypothalamus of freely moving rats were related to sleep and wakefulness using in vivo voltammetry (with carbon fiber microelectrodes) and polygraphic recordings. By using an optoelectronic telemetry system for the voltammetric signals, electrical cross-talk between the two settings was avoided and simultaneous neurochemical and electro-physiological recordings could be made so that a detailed time course of events could be obtained. Extracellular levels of the serotonin metabolite, 5-hydroxy-indoleacetic acid, measured every 2 min, increased with wakefulness and decreased with sleep: levels were significantly lower during desynchronized sleep than slow wave sleep. In vivo voltammetry associated with the optoelectronic telemetry system appears to be a useful tool for studying the relationship between neurochemical changes and electrophysiological events.

Selective blockade of different brain stem muscarinic receptor subtypes: effects on the sleep-wake cycle

Changes induced in the sleep-wake cycle by pontine microinjections of muscarinic antagonists were studied in freely moving rats, instrumented for chronic polygraphic recordings. Pirenzepine (PIR), methoctramine (MET) and p-fluoro-hexahydro-siladifenidol (p-F-HHSiD), which are highly selective M1, M2 and M3 antagonists, respectively, were dissolved in 0.1 microliter of sterile isotonic saline (0.2 microliter of distilled water for p-F-HHSiD) and injected into the pontine reticular nucleus, where the administration of 0.5 microgram carbachol (a mixed muscarinic agonist) induced a 52% increase in the amount of desynchronized sleep (DS) over a 6 h recording period. The blockade of M2 receptors was shown to (i) antagonize DS, by increasing its latency and decreasing its percentage, (ii) decrease slow wave sleep, and (iii) enhance wakefulness. These effects were dose-dependent. No changes in the sleep-wake cycle were observed following microinjection of M1 or M3 antagonists. The results support the hypothesis that at the brain stem level only M2 receptors are involved in sleep mechanisms and, particularly, in the generation and maintenance of DS.

Experimental epilepsy induced by cobalt powder in lower brain-stem and thalamic structures.

Abstract In chronic unrestrained unanaesthetized cats metallic cobalt powder in the lower brain-stem induced, as early as 24h after introduction, marked EEG changes characterized by hypersynchronous potentials, high voltage spikes, spike and wave complexes, generally associated with myoclonic jerks involving facial, cervical and forelimb flexor muscles. These changes generally faded away within 5–6 days. Generalized attacks of myoclonic type were also observed. Sensory stimulation had a driving effect on the electroclinical manifestations. Hypersynchronous potentials were driven by intermittent photic stimulation. The convulsive threshold to Metrazol injection was also definitely lowered. Similar electro-clinical manifestations followed also the introduction of cobalt powder in some midline thalamic nuclei. The results suggest a functional interconnection between some midline thalamic nuclei and lower brain-stem structures in the production of the electro-clinical manifestations of subcortical origin.

Blockade of 5-hydroxytryptamine (serotonin)-2 receptors alters interleukin-1-induced changes in rat sleep

Recent data suggest that interleukin-1-induced enhancement of non-rapid eye movement sleep is mediated, in part, by the serotonergic system. To determine if sleep changes induced by interleukin-1 are mediated by a specific serotonergic receptor subtype, we evaluated interleukin-1 effects on sleep in rats pretreated with the 5-hydroxytryptamine (serotonin)-2 receptor antagonist ritanserin. Ritanserin (0.63 mg/kg, intraperitoneally) by itself did not alter sleep-wake behavior, although it did reduce cortical brain temperature. Interleukin-1 (5 ng, intracerebroventricularly) enhanced non-rapid eye movement sleep, suppressed rapid eye movement sleep, and induced a moderate febrile response. Pretreatment with ritanserin completely blocked the febrile response to interleukin-1 and abolished the interleukin-1-induced enhancement in non-rapid eye movement sleep that occurred during postinjection hours 3-4, without altering interleukin-1 effects on rapid eye movement sleep. The present data suggest that serotonin may partially mediate interleukin-1 effects on sleep by interacting with 5-hydroxytryptamine (serotonin)-2 receptors. These results also suggest that interactions between the serotonergic system and interleukin-1 may be important in regulating sleep-wake behavior.

Depolarization of trigeminal afferents induced by stimulation of brain-stem and peripheral nerves

Summary1.In nembutalized cats the excitability of supraorbital (SO) and infraorbital (IO) primary afferents was tested by microelectrode stimulation within the trigeminal nuclei. SO excitability increased after conditioning stimulation of IO nerve, brain-stem throughout its extent and ipsi- and contralateral fore- and hindlimb nerves. The conditioning curves did not change in decerebrate preparations.2.In decerebrate cats a negative slow potential (trigeminal dorsal root potential, TDRP) was recorded from the isolated sensory trigeminal root following stimulation of contralateral SO nerve, homolateral common radial trunk and brain-stem.3.In nembutalized as in decerebrate cats, a single IO impulse induced in the trigeminal complex a focal synaptic potential (N1-N2-waves) followed by a prolonged (200 msec) slow potential (P-wave). P-waves were also produced by high frequency stimulation of the brain-stem reticular regions. They were positive laterally to the trigeminal nucleus and inverted along a line between nucleus and tract. The N-wave had maximal amplitude in the trigeminal nucleus and became positive at the level of its medial boundary.4.Unit discharges in the trigeminal nucleus responding to IO volley and lemniscal potentials evoked by the same stimulus were depressed by reticular activation following a time course of over 100 msec.5.The results suggest a process of primary afferent depolarization (PAD), of trigeminal fibers induced by stimulations of brain-stem, fore- and hind-limbs nerves and other trigeminal afferents in absence of forebrain and cortical structures.

5-Hydroxytryptophan, but not L-tryptophan, alters sleep and brain temperature in rats.

The precise role of serotonin (5-hydroxytryptamine) in the regulation of sleep is not fully understood. To further clarify this role for 5-hydroxytryptamine, the 5-hydroxytryptamine precursors L-tryptophan (40 and 80 mg/kg) and L-5-hydroxytryptophan (25-, 50-, 75-, 100 mg/kg) were injected intraperitoneally into freely behaving rats 15 min prior to dark onset, and subsequent effects on sleep-wake activity and cortical brain temperature were determined. L-5-hydroxytryptophan, but not L-tryptophan, induced dose-dependent changes in sleep-wake activity. During the 12-h dark period, non-rapid eye movement sleep was inhibited in post-injection hours 1-2 by the two lowest L-5-hydroxytryptophan doses tested, while the two highest doses induced a delayed increase in non-rapid eye movement sleep in post-injection hours 3-12. These highest doses inhibited non-rapid eye movement sleep during the subsequent 12-h light period. The finding that L-5-hydroxytryptophan, but not L-tryptophan, induced a dose-dependent and long-lasting decrease in cortical brain temperature regardless of whether or not non-rapid eye movement sleep was suppressed or enhanced contributes to a growing list of conditions showing that sleep-wake activity and thermoregulation, although normally tightly coupled, may be dissociated. The initial non-rapid eye movement sleep inhibition observed following low doses of L-5-hydroxytryptophan may be attributable to increased serotonergic activity since 5-hydroxytryptamine may promote wakefulness per se, whereas the delayed non-rapid eye movement sleep enhancement after higher doses may be due to the induction by 5-hydroxytryptamine of sleep-inducing factor(s), as previously hypothesized. The period of non-rapid eye movement sleep inhibition beginning 12 h after administration of L-5-hydroxytryptophan doses that increase non-rapid eye movement sleep is characteristic of physiological manipulations in which non-rapid eye movement sleep is enhanced. The results of the present study suggest that the complex effects of 5-HT on sleep depend on the degree and time course of activation of the serotonergic system such that 5-HT may directly inhibit sleep, yet induce a cascade of physiological processes that enhance subsequent sleep.

Stimulation of NMDA and AMPA receptors in the rat nucleus basalis of Meynert affects sleep

The nucleus basalis of Meynert (NBM), a heterogeneous area in the basal forebrain involved in the modulation of sleep and wakefulness, is rich in glutamate receptors, and glutamatergic fibers represent an important part of the input to this nucleus. With the use of unilateral infusions in the NBM, the effects of two different glutamatergic subtype agonists, namely N-methyl-d-aspartic acid (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) hydrobromide, on sleep and wakefulness parameters were determined in freely moving rats by means of polygraphic recordings. NMDA (5 nmol) and AMPA (0.4 nmol) induced an increase in wakefulness and an inhibition of slow-wave sleep. AMPA, but not NMDA, also caused a decrease in desynchronized sleep. These AMPA- and NMDA-mediated effects were counteracted by a pretreatment with the specific NMDA antagonist 2-amino-5-phosphonopentanoic acid (20 nmol) and the specific AMPA antagonist 6,7-dinitroquinoxaline-2,3-dione (2 nmol), respectively. The results reported here indicate that 1) the NBM activation of both NMDA and AMPA glutamate receptors exert a modulatory influence on sleep and wakefulness, and 2) AMPA, but not NMDA receptors, are involved in the modulation of desynchronized sleep, suggesting a different role for NBM NMDA and non-NMDA receptors in sleep modulation.

Depolarization of afferent fibers to the goll and burdach nuclei induced by stimulation of the brain-stem

Summary1.In nembutalized cats the excitability of superficial radial (SR) and superficial peroneus (SP) primary afferents was tested by microelectrode stimulation (Walls technique) within the dorsal column nuclei (DCN). SR and SP excitability increased for over 100 msec after conditioning stimulation of the brain-stem with a maximal effect at 50 msec interval. The conditioning curves did not change in decerebrated and cerebellectomized preparations.2.In nembutalized intact and decerebrated cats a negative slow potential change (over 150 msec) was recorded from one isolated dorsal column (dorsal column potential, DCP) following stimulation of the brain-stem. In the same type of preparations the brain-stem stimulation induced from DCN surface a prolonged (over 150 msec) positive potential (P-wave) which inverted within the nuclei.3.Interaction experiments have revealed an inhibitory effect of conditioning brain-stem stimulation on SR induced surface P-wave. The effect was maximal at 50 msec interval and was present up to 200 msec. SR stimulation also depressed the brain-stem induced P-wave for over 150 msec but with a maximal effect within the first 20–30 msec.4.The effects reported above were maximal when the caudal-most brain-stem regions were stimulated. They were still present in control experiments where the sensorimotor cortex had been widely removed 15 days previously.