The involvement of central alpha adrenoceptors in the antihypertensive actions of methyldopa and clonidine in the rat

Non-rapid eye movement sleep parasomnias

Parasomnias are unpleasant or undesirable behavioral or experiential phenomena that occur during sleep. Once believed unitary phenomena related to psychiatric disorders, it is now clear that parasomnias result from several different phenomena and usually are not related to psychiatric conditions. Parasomnias are categorized as primary (disorders of the sleep states) and secondary (disorders of other organ systems that manifest themselves during sleep). Primary sleep parasomnias can be classified according to the sleep state of origin: rapid eye movement sleep, non-rapid eye movement sleep, and miscellaneous (those not respecting sleep state). Secondary sleep parasomnias are classified by the organ system involved.

NREM sleep parasomnias

The three states of mammalian being--wakefulness, REM sleep, and NREM sleep--are not mutually exclusive and may occur simultaneously, oscillate rapidly, or appear in dissociated or incomplete form to produce primary sleep parasomnias. Dysfunctions of a wide variety of organ systems may take advantage of the sleeping state to declare themselves, resulting in the secondary sleep parasomnias. Contrary to popular opinion, most of these often bizarre and frightening experiences are not the manifestation of underlying psychological or psychiatric conditions. Formal study in an experienced sleep disorders center usually reveals a diagnosable and treatable condition. Various parasomnias may result in injurious or violent behavior. The forensic science implications are beyond the scope of this article but have been reviewed extensively elsewhere. Continued study of unusual sleep-related events undoubtedly will reveal more fascinating conditions, expanding our knowledge of sleep physiology and strengthening the bonds between clinicians and basic science sleep researchers.

Effects of clonidine and alpha-methyl-p-tyrosine on the carbachol stimulation of paradoxical sleep

Acetylcholine promotes paradoxical sleep (PS), but the role of noradrenaline in this stimulation is controversial. The relationship between cholinergic and noradrenergic systems in the production of PS was investigated in the rat implanted on a continuous basis for sleep recordings. Stimulation of PS was obtained with microinjections of carbachol (1 microgram) into the pontine reticular formation. In the presence of the alpha 2-agonist clonidine (5 micrograms/kg, IP), the carbachol activation of PS was abolished. This stimulation also disappeared when the animals were pretreated with alpha-methyl-paratyrosine (150 mg/kg, IP), an inhibitor of catecholamine synthesis. Thus, carbachol stimulation appeared inefficient when brain noradrenergic activation was decreased. This observation supports the view that the realization of PS by the cholinergic system requires a certain level of noradrenergic activity.

Acute intracerebroventricular injections of the mast cell degranulator compound 48/80 and behavior in rats

The intracerebroventricular (ICV) injection of the mast cell degranulator Compound 48/80 (2.5-2.0 micrograms/kg) produced a marked behavioral syndrome in normotensive rats. The behaviors included head and body shakes, paw tremor, excessive grooming, unusual posture and gait, mild diarrhoea, piloerection, extreme agitation and irritability to touch, and a later phase of sedation. The highest doses (15 and 20 micrograms/kg) also produced catalepsy and episodes of "barrel rolling" (continuous rolling of 1-8 turns around the longitudinal axis). These behaviors were observed for approximately 15-30 min although the sedation and catalepsy were maintained for 90-120 min. A second ICV injection of the 10 micrograms/kg dose of Compound 48/80 given 2 hr after an initial injection of this dose, produced a much reduced response and the numbers of head and body shakes, and episodes of paw tremor and grooming were between 20-30% of those produced by the first injection. The reduced effect of the second injection indicates that the behavioral effects of Compound 48/80 may arise from the acute degranulation of mast cells rather than direct effects on neuronal populations or the cerebral vasculature.

Electrophysiological characterization of putative C1 adrenergic neurons in the rat

Recent studies in the rat have demonstrated that at least two populations of sympathoexcitatory reticulospinal neurons reside in the nucleus reticularis rostroventrolateralis. It appears that only one of these populations consists of C1 adrenergic neurons. The present study used both double-labeling (one retrograde tracer and immunohistochemistry) and triple-labeling (two retrograde tracers and immunohistochemistry) to determine if C1 adrenergic neurons, which are immunoreactive for phenylethanolamine N-methyltransferase, exhibit a projection pattern that is sufficiently unique to permit the electrophysiological discrimination between C1 adrenergic and non-adrenergic neurons in the nucleus reticularis rostroventrolateralis. Double-labeling experiments indicated that 71% (range: 53-80) of phenylethanolamine-N-methyltransferase-immunoreactive neurons in the nucleus reticularis rostroventrolateralis could be retrogradely labeled from the thoracic cord, as were 76% (range: 67-94) following tracer injection in the central tegmental tract at pontine levels. Triple-labeling experiments indicated that 88% (range: 82-93) of nucleus reticularis rostroventrolateralis neurons with projections to both spinal cord and central tegmental tract were phenylethanolamine-N-methyltransferase-immunoreactive. Single-unit recording, in nucleus reticularis rostroventrolateralis, was used to identify antidromic potentials elicted from stimulation sites in the spinal cord and/or central tegmental tract. Since clonidine is known to reduce central adrenaline turnover, sensitivity to this drug was used to identify putative adrenergic neurons. Twenty-six nucleus reticularis rostroventrolateralis neurons with axonal projections to both the ipsilateral spinal cord and the central tegmental tract were recorded in halothane-anesthetized rats. All these cells were barosensitive, pulse-modulated, and 16 of the 16 cells tested exhibited a 66 +/- 8% reduction in activity upon the intravenous administration of clonidine (20 micrograms/kg). Most (13 out of 16) exhibited a strong respiratory modulation. The conduction velocity of their spinal collateral was generally low (0.9 +/- 0.1 m/s) and their firing rate moderate (7.4 +/- 1.2 spikes/s). Forty-three nucleus reticularis rostroventrolateralis cells with axonal projections exclusively to the thoracic cord were studied for comparison. These cells were strongly barosensitive and pulse-synchronous, had a high discharge rate (25 +/- 3 spikes/s) and a moderate conduction velocity (3.4 +/- 0.3 m/s). Only one of the 15 cells tested was inhibited by clonidine and only two to these 15 cells exhibited a detectable respiratory modulation. Thus barosensitive nucleus reticularis rostroventrolateralis neurons with axonal projections to both the spinal cord and the central tegmental tract likely belong to the C1 adrenergic cell group. It is concluded that this subgroup of adrenergic neurons probably subserves a vasomotor function.

Body temperature during and following 10-day subcutaneous infusion of clonidine in the rat

Body temperature in the rat was measured during and after cessation of the continuous subcutaneous infusion of clonidine (10 micrograms/kg per hr) for 10 days. The body temperature of control animals displayed a distinct circadian rhythm. On each day the mean body temperature over the dark phase (2000-0800 hr) was consistently higher (0.6-0.9 degrees C) than the following light phase. The infusion of clonidine was essentially devoid of initial effects on body temperature. However, during the light phases of day 2 onwards the mean body temperature of the animals treated with clonidine was consistently higher (0.4-0.6 degrees C) than that of controls. No such differences were observed during the dark phases. It appeared that the infusion of clonidine limited the fall in body temperature which normally occurred at the onset of the light phases and this resulted in the treated rats displaying a relative hyperthermia. On cessation of the infusion of clonidine (at 2400 hr on day 11) a distinct hyperthermia was observed within 2 hr and was sustained for the remainder of the dark phase and subsequent light phase. This post-infusion hyperthermia was more pronounced than that observed during the period of infusion of clonidine. These results demonstrate that the circadian control of body temperature is disturbed both during and after continuous infusion of clonidine.