Which mediator is responsible for hyperalgesia during hemodynamic fluctuations at the spinal cord level?

At the spinal cord level, this mediator is dopamine. The process is triggered by serotonergic structures of the nucleus raphe magnus.

As part of which tract do the fibers of the antianalgesic system travel?

Processes of neurons from the dorsal and magnus raphe nuclei travel to spinal cord cells as part of the ventral tract.

How do cytokines trigger hyperalgesia during inflammation?

Cytokines first activate neurons of the nucleus of the solitary tract (NTS), which subsequently induce excitation in the nucleus raphe magnus. From there, impulses travel via the dorsolateral funiculi to the dorsal horns of the spinal cord.

What mediators are released in the spinal cord during inflammatory hyperalgesia?

Primary mediators include substance P, cholecystokinin, N-methyl-D-aspartate (NMDA), and nitric oxide (NO).

Home › Physiology › Mechanisms of Hyperalgesia and Antianalgesia

Mechanisms of Hyperalgesia and Antianalgesia

Hyperalgesia et antianalgesia

For medical students2 min readUpdated 2026-10-10

Hyperalgesia (increased pain sensitivity) and antianalgesia (suppression of pain relief) are mediated through descending influences of the central nervous system on spinal cord neurons. These complex processes are triggered by various factors, including hemodynamic fluctuations and systemic or local inflammation, and are strictly mediated by specific neurotransmitters.

HemodynamicsBlood pressure fluctuations trigger hyperalgesia via dopamine release

Raphe NucleiMajor pain modulation centers (dorsal and magnus raphe nuclei)

CytokinesAct as primary triggers during inflammatory processes

InflammationReleases substance P, cholecystokinin, NMDA, and NO in the spinal cord

Hemodynamic Influence on Pain Sensitivity

Changes in blood flow parameters and blood pressure fluctuations within the vascular bed act as a powerful physiological trigger capable of modulating pain perception and inducing hyperalgesia. This process is mediated by the activation of specialized serotonergic structures in the brainstem.

A key role in this reflex chain is played by the Nucleus raphe magnus (large raphe nucleus). Descending signals from these brainstem structures project to the segmental apparatus. Notably, in hemodynamically induced hyperalgesia, the primary chemical transmitter at the spinal cord neuron level is dopamine. It is responsible for the ultimate enhancement of nociceptive signaling.

Antianalgesic System and Pronociceptive Effects

The central nervous system possesses mechanisms capable of actively blocking pain relief processes. This phenomenon is termed the antianalgesic effect. Its source is neuronal populations of two important brainstem structures: the dorsal raphe nucleus and the nucleus raphe magnus.

The processes of these nerve cells form descending pathways directed toward spinal cord neurons as part of the ventral tract. The net physiological effect of this descending pathway is facilitatory, or pronociceptive—it promotes easier conduction of pain signals. At the spinal cord segment level, this antianalgesic effect is realized through the release of a specific neuropeptide—cholecystokinin.

Neurochemical Cascade in Inflammation

Inflammatory reactions, whether a systemic process or a local focus, inevitably lead to pronounced hyperalgesia. The primary triggering factor consists of inflammatory mediators, among which a dominant role is assigned to cytokines.

The activation process represents a multi-step chain:

Cytokines activate neurons of the solitary tract nucleus (Nucleus tractus solitarii, NTS).
The signal is transmitted from the NTS, inducing strong excitation in the nucleus raphe magnus.

Following processing in the raphe structures, a primary descending impulse flow is formed. It projects to the dorsal horns of the spinal cord via the dorsolateral funiculi. Upon reaching the target, a spectrum of hyperalgesic mediators is released:

Substance P (Substance P);
Cholecystokinin;
N-methyl-D-aspartate (NMDA);
Nitric oxide (NO).

Mnemonic

Memory aids: Pressure — Dopamine. Ventral tract — Cholecystokinin (Antianalgesia). Inflammation — Full set (Substance P, Cholecystokinin, NMDA, NO).

Frequently asked questions

Which mediator is responsible for hyperalgesia during hemodynamic fluctuations at the spinal cord level?: At the spinal cord level, this mediator is dopamine. The process is triggered by serotonergic structures of the nucleus raphe magnus.
As part of which tract do the fibers of the antianalgesic system travel?: Processes of neurons from the dorsal and magnus raphe nuclei travel to spinal cord cells as part of the ventral tract.
How do cytokines trigger hyperalgesia during inflammation?: Cytokines first activate neurons of the nucleus of the solitary tract (NTS), which subsequently induce excitation in the nucleus raphe magnus. From there, impulses travel via the dorsolateral funiculi to the dorsal horns of the spinal cord.
What mediators are released in the spinal cord during inflammatory hyperalgesia?: Primary mediators include substance P, cholecystokinin, N-methyl-D-aspartate (NMDA), and nitric oxide (NO).

Go deeper

Role of serotonergic structures of the nucleus raphe magnus in pain modulation
Specifics of pronociceptive and antinociceptive effects of the central nervous system
Interaction of cytokines with neurons of the nucleus of the solitary tract
Topography of descending pathways: dorsolateral funiculi and ventral tract
Mechanisms of action of nitric oxide (NO) and NMDA in the dorsal horns of the spinal cord