Adrenoreceptor modulation of oromotor pathways in the rat medulla

Abstract

Regulation of feeding behavior involves the integration of multiple physiological and neurological pathways that control both nutrient-seeking and consummatory behaviors. The consummatory phase of ingestion includes stereotyped oromotor movements of the tongue and jaw that are controlled through brain stem pathways. These pathways encompass not only cranial nerve sensory and motor nuclei for processing feeding-related afferent signals and supplying the oromotor musculature but also reticular neurons for orchestrating ingestion and coordinating it with other behaviors that utilize the same musculature. Based on decerebrate studies, this circuit should be sensitive to satiety mechanisms mediated centrally by A2 noradrenergic neurons in the caudal nucleus of the solitary tract (cNST) that are potently activated during satiety. Because the first observable phase of satiety is inhibition of oromotor movements, we hypothesized that norepinephrine (NE) would act to inhibit prehypoglossal neurons in the medullary reticular formation. Using patch-clamp electrophysiology of retrogradely labeled prehypoglossal neurons and calcium imaging to test this hypothesis, we demonstrate that norepinephrine can influence both pre- and postsynaptic properties of reticular neurons through both α1- and α2-adrenoreceptors. The α1-adrenoreceptor agonist phenylephrine (PE) activated an inward current in the presence of TTX and increased the frequency of both inhibitory and excitatory miniature postsynaptic currents. The α2-adrenoreceptor agonist dexmedetomidine (DMT) inhibited cNST-evoked excitatory currents as well as spontaneous and miniature excitatory currents through presynaptic mechanisms. The diversity of adrenoreceptor modulation of these prehypoglossal neurons may reflect their role in a multifunctional circuit coordinating both ingestive and respiratory lingual function.

Dopamine and Noradrenaline in the Brain; Overlapping or Dissociate Functions?

“…Depending on the neuronal targets and their specific receptors, DA and NA can modulate various intrinsic currents and hence excitability of the neurons (McCormick, 1989;Cathala and Paupardin-Tritsch, 1999;Seamans and Yang, 2004;Rosenkranz and Johnston, 2006;Arencibia-Albite et al, 2007). The most prominent effect of the NA is the modulation of synaptic transmission and various forms of plasticity (Harley, 1987;Mouradian et al, 1991;Sara, 2009), which are analogous to those of DA (Seamans and Yang, 2004;Tritsch and Sabatini, 2012;Froemke, 2015). In various sensory systems, both dopaminergic and noradrenergic systems were effective in remodeling the tuning properties of the cortical neurons (Bao et al, 2001;Manunta and Edeline, 2004;Edeline et al, 2011;Martins and Froemke, 2015;McBurney-Lin et al, 2019;Waterhouse and Navarra, 2019).…”

Neural Control of the Upper Airway: Respiratory and State‐Dependent Mechanisms

“…In different pools of respiratory motoneurons, the two opposing effects may have different magnitudes. Similarly, data from medullary slices from neonatal rats indicate that XII premotor neurons of the IRt region can be controlled by both the excitatory α 1 -adrenoceptors that are often located postsynaptically and the inhibitory α 2 -adrenoceptors that appear to be mainly located on synaptic terminals contacting these premotor neurons (presynaptically) (368). …”

“…Therefore, if any relevant for these experiments antagonism of NE and 5-HT receptors occurred outside the XII nucleus, its targets could be distal dendrites of XII motoneurons and possibly cell bodies and terminals of XII premotor neurons located in the IRt region lateral and ventrolateral to the XII nucleus (Fig. 3) because these cells may also have NE and 5-HT receptors (368). …”

Intake Regulation

“…Norepinephrin appears to slow eating behavior by inhibiting motor neurons in the medulla involved in the involuntary control of ingestion and swallowing (Nasse and Travers, 2014). The D1 receptors in the hypothalamus promote food intake, while D2 receptors inhibit it.…”