Reticular activating system

Barbiturates produce CNS depression, which ranges from sedation to general anesthesia. Action is through suppression of the mesencephalic reticular activating system. Barbiturates enhance GABA-induced inhibition the site of inhibition may be presynaptic in the spinal cord or postsynaptic in the cortical... 

Ascending inputs from the brainstem ascending reticular activating system (ARAS). As described below, these seem to be particularly important and probably disrupt the thalamo-cortical synchrony. 

Figure 22.5 Pathways involved in cortico-thalamic synchrony and EEG arousal. The ascending reticular activating system (ARAS) extends from the cephalic medulla through the pons and midbrain to the thalamus (see Moruzzi and Mayoun 1949). It is activated by impulses in collaterals of the spinothalamic sensory pathway running to specific thalamic nuclei (SpThNc) and in turn activates much of the cortex, partly through the non-specific thalamic nuclei (NspThNc), which also receive inputs from SpThNc and also via the nucleus basalis (NcB). Its stimulation is followed by EEG arousal. It is probable that reciprocal links between cortical areas and the thalamus, particularly NspThN, lead to slow-wave (8 Hz) cortical EEG synchrony and, in the absence of appropriate sensory input and ARAS activity, a sleep state...

Direct and indirect connections to the reticular activating system (RAS), a region spanning the medulla, pons, and midbrain, help to regulate arousal, vigilance, and fear. Modulation of these connections relies on the neurotransmitters serotonin... 

The basal forebrain is an important way station in the activation of the cerebral cortex from the reticular activating system. AMPA and NMDA injections into the basal forebrain increase wakefulness and reduce sleep (Cape Jones, 2000 Manfridi et al, 1999), effects that are blocked by AMPA and NMDA receptor antagonists (Manfridi et al, 1999). The excitatory cortical projections of the basal forebrain have long been considered purely cholinergic, but many basal forebrain neurons that project to the cortex are now known to contain Glu, which may function as a co-transmitter or even as the primary excitatory neurotransmitter (Manns et al, 2001). The basal forebrain also affects vigilance via synapses to HCT cells in the lateral hypothalamus some of these synapses are glutamatergic (Henny Jones, 2006). 

Ascending Reticular Activating System (ARAS) A network of neurons running up (ascending) through the core of the brainstem to the diencephalon and descending to the spinal cord. Also known as the reticular formation. 

ARAS ascending reticular activating system CHE cholinesterase... 

Originating in a discrete locus or loci of co-ordinated neurons with either direct or indirect (e.g. via GABA interneurons) reciprocal connections with such key areas as cortex, thalamus and brainstem reticular activating system. 

Mechanism of Action Abarbiturate that binds at the GABA receptor complex, enhancing GABA activity. Therapeutic Effect Depresses central nervous system (CNS) activity and reticular activating system. 

The medulla is the ultimate center for regulating vegetative functions such as respiration, swallowing, heart rate, and blood pressure. Related to respiration are the coughing and vomiting reflexes also associated with this part of the brain. The medulla is a type of crossroads where various neuron bundles go into and out of the brain. The reticular activating system or RAS, a part of the diffuse group of neurons known as the reticular formation. 

Plasma protein binding of LSD is >80%. As the drug penetrates the CNS, it is concentrated in the visual brain areas and the limbic and reticular activating systems, correlating with perceived effects. LSD is also found in the liver, spleen, and lungs.5 The volume of distribution is reported to be low at 0.28 L/kg.1 Wagner et al.6 described a two-compartment open model for LSD with an elimination half-life of 3 h. 

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