Noradrenerge

Noradrenerge, or noradrenergic, refers to the biological systems that use norepinephrine (noradrenaline) as their primary neurotransmitter or signaling molecule. In the central nervous system, noradrenergic neurons arise mainly from the locus coeruleus and surrounding brainstem nuclei, projecting widely to cortex, thalamus, limbic system, and spinal cord, where they modulate arousal, attention, learning, memory, and stress responses. In the peripheral nervous system, noradrenergic neurons are the principal postganglionic fibers of the sympathetic division of the autonomic nervous system, releasing norepinephrine onto target organs to regulate cardiovascular function, metabolism, and smooth muscle tone.

Receptors: Norepinephrine acts on adrenergic receptors (alpha and beta). Alpha-1 receptor activation leads to vasoconstriction and increased peripheral resistance; alpha-2 receptors modulate neurotransmitter release via negative feedback. Beta-1 receptors increase heart rate and contractility; beta-2 receptors cause bronchodilation and metabolic effects. The net physiological responses depend on receptor distribution and plasma levels.

Pharmacology: Noradrenergic signaling can be enhanced or dampened by medications. Uptake inhibitors such as serotonin-norepinephrine reuptake inhibitors (SNRIs) and tricyclic antidepressants raise synaptic norepinephrine. Monoamine oxidase inhibitors prevent breakdown of norepinephrine. Selective norepinephrine reuptake inhibitors like atomoxetine are used in attention-deficit/hyperactivity disorder. Receptor agonists and antagonists include phenylephrine (alpha-1 agonist), clonidine (alpha-2 agonist), and beta blockers such as propranolol. Clinically, noradrenergic dysregulation is implicated in mood disorders, anxiety, ADHD, and the body's stress response.