Reticular formation

The second cluster of neurons lies more caudally, near the pons, in the pedunculo-pontine (PPT) and laterodorsal tegmental (LDT) nuclei (see Fig. 22.6) and could be regarded as part of the ARAS (see McCormick 1992). It innervates the non-specific thalamic nuclei as well as some more specific ones like the lateral geniculate nucleus (visual pathway), the pontine reticular formation and occipital cortex. Because long... 

In fact, there is a good deal of evidence to support this suggestion. First, more than half the neurons in the PPT fire rhythmically only when PGO waves are evident and their firing starts immediately before the PGO waves appear. Second, in cats, REM sleep is augmented by direct injection of either carbachol, or more selective muscarinic agonists, or the anticholinesterase, neostigmine, into the pontine reticular formation (one of the projection sites for PPT). Third, REM sleep is abolished by lesion of the PPT nucleus but, interestingly, not by lesion of the LDT. 

McCormick, DA (1992) Neurotransmitter actions in the thalamus and cerbral cortex and their role in neuromodulation of thalamocortical activity. Prog. Neurobiol. 39 3778-3788. Moruzzi, G and Mayoun, HW (1949) Brainstem reticular formation and activation of the EEG. EEG Clin. Neurophysiol. 1 455-473. 

Fisher, L.J. Young, S.J. Tepper. J.M. and Groves, P.M. Reticular formation stimulation modifies cortically evoked intracellular potentials in neostriatum of rat, Abstr Soc Neurosci 13 979. 1987. 

The extrapyramidal motor system controls muscle movement through a system of pathways and nerve tracts that connect the cerebral cortex, basal ganglia, thalamus, cerebellum, reticular formation, and spinal neurons. Patients with PD lose dopamine neurons in the substantia nigra, which is located in the midbrain within the brain stem. The substantia... 

In addition, the brainstem contains a diffuse network of neurons known as the reticular formation. This network is best known for its role in cortical alertness, ability to direct attention, and sleep. It is also involved with coordination of orofacial motor activities, in particular those involved with eating and the generation of emotional facial expressions. Other functions include coordination of eating and breathing, blood pressure regulation, and response to pain. 

Signals are also transmitted to the reticular formation of the brainstem by way of the spinoreticular tract. The reticular formation plays an important role in the response to pain. First, it facilitates avoidance reflexes at all levels of the spinal cord and, second, it is responsible for the significant arousal effects of pain. Signals from the reticular formation cause an increase in the electrical activity of the cerebral cortex associated with increased alertness. Furthermore, it sends nerve impulses to the hypothalamus to influence its functions associated with sudden alertness, such as increased heart rate and... 

Figure 8.1 The pain pathway. The pain signal is transmitted to several regions of the brain, including the thalamus reticular formation hypothalamus limbic system and somatosensory cortex. Each region carries out a specific aspect of the response to pain.

Nerve signals from the thalamus and the reticular formation are transmitted to the limbic system as well as the hypothalamus. Together, these regions of the brain are responsible for behavioral and emotional responses to pain. The limbic system, in particular, may be involved with the mood-altering and attention-narrowing effect of pain. 

The amino acid glutamate is the most widely used excitatory neurotransmitter in the central nervous system of mammals. Glutamate is the primary neurotransmitter used by the vast majority of reticular formation, thalamic and cortical neurons, which play a crucial role in the generation of the characteristic electrical activity as recorded in the electroencephalogram (for details see Steriade McCarley (2005)). The activity of these neurons is tightly regulated by the other neurotransmitters described in this chapter. 

Baghdoyan, H. A. Lydic, R. (1999). M2 muscarinic receptor subtype in the feline medial pontine reticular formation modulates the amount of rapid eye movement sleep. Sleep 22, 835-47. 

Baghdoyan H. A., Monaco, A. P., Rodrigo-Angulo, M. L. et al. (1984a). Microinjection of neostigmine into the pontine reticular formation of cats enhances desynchronized sleep signs. J. Pharmacol. Exp. Then 231, 173-80. 

Greene, R. W., Gerber, U. McCarley, R. W. (1989). Cholinergic activation of medial pontine reticular formation neurons in vitro. Brain Res. 476, 154-9. 

Mitler, M. M. Dement, W. C. (1974). Cataplectic-like behavior in cats after micro-injections of carbachol in pontine reticular formation. Brain Res. 68, 335-43. 

Vincent, S. R., Satoh, K, Armstrong, D. M. Fibiger, H. C. (1983). NADPH-diaphorase a selective histochemical marker for the cholinergic neurons of the pontine reticular formation. Neurosci. Lett. 43, 31-6. 

Lydic, R. Baghdoyan, H. A. (1993). Pedunculopontine stimulation alters respiration and increases ACh release in the pontine reticular formation. Am. J. Physiol. 264, R544-54. 

Semba, K. (1993). Aminergic and cholinergic afferents to REM sleep induction regions of the pontine reticular formation in the rat. J. Comp. Neurol. 330, 543-56. 

Vazquez, J. Baghdoyan, H. A. (2004). GABAA receptors inhibit acetylcholine release in cat pontine reticular formation implications for REM sleep regulation. J. Neurophysiol. 92, 2198-206. 

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