How does the sympathetic reaction work in dogs when bitten by ticks? - briefly
When a tick pierces a dog’s skin, sensory nerves activate the sympathetic branch, causing rapid release of norepinephrine that raises heart rate, constricts peripheral vessels, and mobilizes energy stores. This response prepares the animal to counteract stress and limit blood loss at the bite site.
How does the sympathetic reaction work in dogs when bitten by ticks? - in detail
When a tick attaches to a canine, its mouthparts penetrate the skin and introduce saliva containing anticoagulants, anti‑inflammatory agents, and microbial antigens. Sensory nerve endings in the dermis detect tissue injury and chemical stimuli, generating afferent signals that travel via spinal nerves to the dorsal horn of the spinal cord. From there, the information is relayed to the brainstem and hypothalamus, which coordinate activation of the sympathetic division of the autonomic nervous system.
The hypothalamus stimulates the intermediolateral cell column of the thoracic spinal cord, sending pre‑ganglionic fibers to the sympathetic chain ganglia. Post‑ganglionic neurons release norepinephrine onto target organs, producing the classic fight‑or‑flight pattern:
- Cardiovascular effects: heart rate rises, contractility increases, peripheral arterioles constrict, and blood pressure elevates to improve perfusion of vital tissues.
- Respiratory adjustments: bronchi dilate, facilitating increased oxygen intake.
- Metabolic shifts: glycogenolysis and lipolysis are accelerated, providing glucose and free fatty acids for immediate energy use.
- Thermoregulatory response: sweat glands (in dogs, primarily paw pads) are activated, and panting may intensify to dissipate heat generated by heightened metabolism.
- Pupil dilation: iris dilator muscle contracts, enhancing visual acuity for threat assessment.
Simultaneously, the adrenal medulla receives direct pre‑ganglionic input, secreting epinephrine and additional norepinephrine into the bloodstream. These circulating catecholamines amplify and prolong the peripheral sympathetic effects, ensuring systemic readiness.
The rapid mobilization of cardiovascular, respiratory, and metabolic resources helps the animal cope with the acute stress of parasitic intrusion and limits the spread of potential pathogens introduced by the tick. Persistent activation, however, can exacerbate underlying cardiac conditions and increase the risk of arrhythmias, especially in breeds predisposed to heart disease.
Understanding this cascade clarifies why tick bites often trigger observable signs such as tachycardia, dilated pupils, heightened alertness, and increased panting. Prompt removal of the ectoparasite and monitoring of autonomic signs are essential components of veterinary management.