Forebrain projections to brainstem nuclei involved in the control of mandibular movements in rats

Abstract

Mandibular movements occur through the triggering of trigeminal motoneurons. Aberrant movements by orofacial muscles are characteristic of orofacial motor disorders, such as nocturnal bruxism (clenching or grinding of the dentition during sleep). Previous studies have suggested that autonomic changes occur during bruxism episodes. Although it is known that emotional responses increase jaw movement, the brain pathways linking forebrain limbic nuclei and the trigeminal motor nucleus remain unclear. Here we show that neurons in the lateral hypothalamic area, in the central nucleus of the amygdala, and in the parasubthalamic nucleus, project to the trigeminal motor nucleus or to reticular regions around the motor nucleus (Regio h) and in the mesencephalic trigeminal nucleus. We observed orexin co-expression in neurons projecting from the lateral hypothalamic area to the trigeminal motor nucleus. In the central nucleus of the amygdala, neurons projecting to the trigeminal motor nucleus are innervated by corticotrophin-releasing factor immunoreactive fibers. We also observed that the mesencephalic trigeminal nucleus receives dense innervation from orexin and corticotrophin-releasing factor immunoreactive fibers. Therefore, forebrain nuclei related to autonomic control and stress responses might influence the activity of trigeminal motor neurons and consequently play a role in the physiopathology of nocturnal bruxism.

Complex movement disorders at disease onset in childhood narcolepsy with cataplexy

“…This presentation was highly stereotyped and specific for rapidly evolving narcolepsy with cataplexy, suggesting it is a direct reflection of an acute failure of hypocretinergic neurotransmission. In this context, the prominent facial involvement may reflect the primary importance of the hypocretinergic facilitation of motoneuron activity at the level of the multiply-innervated muscle fibres of the facial muscles (Schreyer et al ., 2009) and of the trigeminal motor nuclei (Mascaro et al ., 2009), while the mild generalized hypotonia could correspond to an abrupt general lack of facilitation of spinal cord motoneurons (Yamuy et al ., 2004). …”

Oromotor Nuclei

“…Although one brief report describes a few direct cortico-trigeminal fibers, and short latency responses, that might result from descending cortical projections onto 5N dendrites that extend into the lateral tegmental field (Ohta and Sasamoto, 1980), the predominant view is that most forebrain pathways are not direct to 5N neurons, with the one likely exception of a projection from the hypothalamus. Thus, retrograde tracers injected into 5N label motor cortex, the central nucleus of the amygdala, the lateral hypothalamus and the bed nucleus of the stria terminalis, but complimentary anterograde marker injections into these forebrain sites typically result in considerably more label in the area surrounding 5N rather than within the nuclear boundaries, suggesting that retrograde injections spilled over into the adjacent RF (Mascaro et al, 2009;Yoshida et al, 2009). These descending projections to the RF however, show a degree of specificity (Fig.…”

“…More recently, the region just medial to the ventromedial subdivision of 5N (MPe5) has been identified as having a close association with adjacent jaw-opener motoneurons (McDavid et al, 2006;Yoshida et al, 2009). These RF regions surrounding 5N (initially designated Regio h in rabbit (Meesen and Olszewski, 1949)) receive numerous inputs to influence 5N neurons, including projections from the red nucleus (Godefroy et al, 1998) the midline pontine and medullary RF (rabbit: Kolta et al, 2000), the central nucleus of the amygdala, lateral hypothalamus, the bed nucleus of the stria terminalis (Mascaro et al, 2009), and cortex (Yoshida et al, 2009).…”

Connections of the lateral hypothalamic area juxtadorsomedial region in the male rat

“…The above regions, each of which connect with the MRN, are indicated to have involvement in a very wide range of functions, including behavioral state control (dorsal raphe) (Nitz and Siegel, 1997;Millan, 2003;Waselus et al, 2011), parasympathetic control (PSTN) (Goto and Swanson, 2004;Ciriello et al, 2008), gustation and viscerosensation (PB, PSTN) (Spector, 1995;Goto and Swanson, 2004;Geerling and Loewy, 2008), thermogenesis (PB) (Morrison and Nakamura, 2011), orofacial motor control (PSTN, RR, STN, SN) (Goto and Swanson, 2004;Hamani et al, 2004;Mascaro et al, 2009), locomotion (SN, STN) (Blandini et al, 2000;Hamani et al, 2004), motivational value (VTA, LH) (Ikemoto, 2007;Matsumoto and Hikosaka, 2007;Jhou et al, 2009;Ikemoto, 2010), and ingestive behavior and energy homeostasis (anterior BST) (Dong and Swanson, 2003, 2004, 2006a.…”