Neurohormone

Definition

A hormone synthesized and released by neurosecretory cells (neuroendocrine cells) into the circulatory system to act on distant target tissues. In arthropods, neurohormones are produced primarily in the brain, especially the corpora cardiaca, and regulate fundamental physiological processes including molting, metamorphosis, reproduction, diapause, and metabolism. Unlike neurotransmitters, which act across synaptic clefts, neurohormones travel via hemolymph to exert systemic effects, though some may also function locally in paracrine or autocrine signaling.

Etymology

From Greek neuron (nerve) + hormon (to set in motion, excite)

Example

In the tobacco hornworm (Manduca sexta), the neurohormone prothoracicotropic hormone (PTTH) is released from the corpora cardiaca in response to environmental cues, stimulating the prothoracic glands to synthesize and secrete ecdysone, thereby initiating the molt to the next instar.

Synonyms

• neurosecretory hormone

Related Terms

• Neurotransmitter
• corpus cardiacum
• corpus allatum
• Ecdysone
• Juvenile hormone
• prothoracicotropic hormone
• neurosecretory cell
• endocrine system
• molting

Usage Notes

Distinguish from neurotransmitter: neurohormones act systemically via circulation, whereas neurotransmitters act locally across synapses. The term is sometimes used more broadly to include any signaling molecule released by neurons, but in entomological and physiological contexts, the circulatory delivery criterion is standard. Arthropod neurohormones are often peptide-based and produced in specialized neurohemal organs.