How does ultrasound affect mice and rats? - briefly
Low‑intensity ultrasound transiently modulates neuronal firing and can evoke measurable behavioral changes in rodents; higher intensities may produce tissue heating and potential damage. The magnitude and nature of these effects depend on frequency, intensity, exposure duration, and the specific brain region targeted.
How does ultrasound affect mice and rats? - in detail
Ultrasonic exposure influences rodents through mechanical and thermal mechanisms that alter cellular activity, tissue integrity, and behavior. Frequencies commonly employed range from 0.5 MHz to 5 MHz, with intensity levels spanning 0.1 W cm⁻² to 3 W cm⁻². Duration of application varies from milliseconds in neuromodulation protocols to several minutes in therapeutic studies. Parameter selection determines the balance between reversible functional modulation and irreversible tissue damage.
Physiological effects include:
- Mechanical displacement of cell membranes, leading to activation of stretch‑sensitive ion channels and subsequent changes in neuronal firing patterns.
- Localized heating, typically <1 °C at low intensities, which can modify enzyme kinetics and metabolic rates without causing necrosis.
- Cavitation events at higher pressures, producing micro‑bubbles that may disrupt vascular endothelium and facilitate transient opening of the blood‑brain barrier.
Behavioral outcomes observed in laboratory mice and rats comprise:
- Modulation of pain perception; low‑intensity pulsed ultrasound reduces nociceptive responses in tail‑flick and hot‑plate assays.
- Altered locomotor activity; focused ultrasound applied to motor cortex induces transient changes in gait speed and stride length.
- Anxiety‑related behaviors; chronic exposure at sub‑thermal levels can decrease time spent in open arms of elevated plus‑maze tests, suggesting stress‑inducing effects.
Neurological investigations reveal:
- Enhanced synaptic plasticity in hippocampal slices after brief ultrasonic bursts, evidenced by increased long‑term potentiation magnitude.
- Activation of specific brain regions measured by functional magnetic resonance imaging, with blood‑oxygen‑level‑dependent signals rising in auditory and somatosensory cortices within seconds of stimulation.
- Gene expression shifts; up‑regulation of c‑Fos and BDNF transcripts occurs in cortical tissue following repeated sessions, indicating activity‑dependent transcriptional responses.
Safety considerations emphasize:
- Adherence to Mechanical Index (MI) below 0.5 to prevent cavitation‑induced hemorrhage.
- Monitoring of core temperature to avoid hyperthermia; continuous rectal thermometry is recommended during prolonged exposures.
- Species‑specific thresholds; rats generally tolerate higher acoustic pressures than mice due to larger cranial dimensions and differing skull attenuation properties.
Experimental applications exploit these effects for:
- Non‑invasive neuromodulation, enabling reversible suppression or excitation of targeted neuronal circuits without surgical implants.
- Targeted drug delivery, where transient blood‑brain barrier disruption permits passage of macromolecules that otherwise cannot cross.
- High‑resolution imaging, utilizing ultrasound‑mediated contrast agents to enhance vascular delineation in small‑animal models.
Overall, ultrasonic interaction with rodent models presents a versatile tool for probing physiological processes, modulating behavior, and delivering therapeutic agents, provided that exposure parameters remain within established safety margins.