Pontine 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. 

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. 

Bourgin, P., Escourrou, P., Gaultier, C. Adrien, J. (1995). Induction of rapid eye movement sleep by carbachol infusion into the pontine reticular formation in the rat. Neuroreport 6, 532-6. 

The most recent species to be studied with respect to cholinergic REM sleep enhancement is mouse (Lydic et al, 2002). Microinjection of neostigmine into the pontine reticular formation of C57BL/6J (B6) mouse has now been shown to cause a REM sleep-like state (Fig. 5.3). REM sleep also can be enhanced in B6.v-lepob... 

REM sleep (Kodama et al, 1990 Leonard Lydic, 1995, 1997) and cholinergic REM sleep enhancement (Lydic et al., 1991), ACh release is significantly increased in the same regions of the pontine reticular formation where microinjection of cholinomimetics enhances REM sleep (1.3 and 1.4 on Fig. 5.1). These results support the conclusion that at the level of ACh release, the cholinergic enhancement of REM sleep is a faithful model of spontaneous REM sleep. 

ACh regulates the cortical arousal characteristic of both REM sleep and wakefulness (Semba, 1991, 2000 Sarter Bruno, 1997, 2000). Medial regions of the pontine reticular formation (Figs. 5.2 and 5.7) contribute to regulating both the state of REM sleep and the trait of EEG activation. Within the medial pontine reticular formation, presynaptic cholinergic terminals (Fig. 5.1) that release ACh also are endowed with muscarinic cholinergic receptors (Roth et al, 1996). Autoreceptors are defined as presynaptic receptors that bind the neurotransmitter that is released from the presynaptic terminal (Kalsner, 1990). Autoreceptors provide feedback modulation of transmitter release. Autoreceptor activation... 

C) and (D) highlight a cholinergic LDT/PPT neuron (C) that was identified via retrograde fluorescent tracer (D) as projecting to the medial pontine reticular formation. (Modified from Lydic Baghdoyan, 2005). (See also Plate 4.)... 

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