Fictive Scratching Patterns in Brain Cortex-Ablated, Midcollicular Decerebrate, and Spinal Cats

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Physiology

Background:

• Existing models for spinal cord central pattern generators (CPGs), including the symmetrical half-center hypothesis, burst generators, computational models, and connectome circuits, are reviewed.
• Asymmetrical models, contrasting with the half-center paradigm, incorporate extensor and flexor CPG modules, potentially including motoneurons for biarticular muscles.
• The study addresses the unknown suitability of different CPG models for explaining specific characteristics of fictive scratching (FS) in cats.

Purpose of the Study:

• To investigate fictive scratching (FS) patterns in cats, focusing on the aiming phase (AP) and rhythmic periods (RP).
• To examine the effects of serotonin (5HT) and segmental inputs on FS.
• To determine the most suitable model for explaining FS, particularly the AP in the midcollicular (MCC) preparation.

Main Methods:

• Experiments were conducted on brain cortex-ablated cats (BCAC), spinalized (SC) cats, and in the midcollicular (MCC) preparation.
• Subjects were immobilized, and peripheral nerves were used for monosynaptic reflex (MR) elicitation, scratching pattern modification, and electroneurogram (ENG) recordings.
• Serotonin (5HT) and WAY 100635 (5HT1A antagonist) were applied; electrical stimulation of afferent fibers and nerve stimulation were performed.

Main Results:

• In BCAC, FS was induced by pinna stimulation or serotonin; AP initiated with flexor or extensor motoneuron activation. Serotonin during AP caused simultaneous flexor and extensor bursts.
• In SC, RP activity was recorded in soleus motoneurons. Serotonin or WAY induced FS bouts. Ia afferent stimulation caused waxing and waning of heteronymous MRes.
• In MCC, FS began with flexor activity. Stimulation of peroneus nerves increased tibialis anterior (TA) ENG duration. Medial gastrocnemius (MG) manipulation reduced TA ENG and initiated MG extensor bursts; MRes waxed and waned.

Conclusions:

• Descending pathways, segmental afferent fibers, serotonin (5HT), and WAY 100635 can alter fictive scratching (FS) patterns.
• The symmetrical half-center hypothesis is considered the most appropriate model for explaining the aiming phase (AP) of FS in the midcollicular (MCC) preparation.
• Findings highlight the complex interplay of neural inputs and neuromodulators in shaping spinal motor output for behaviors like scratching.