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

Background: The spinal cord's central pattern generators (CPGs) have been explained by the symmetrical half-center hypothesis, the bursts generator, computational models, and more recently by connectome circuits. Asymmetrical models, at odds with the half-center paradigm, are composed of extensor and flexor CPG modules. Other models include not only flexor and extensor motoneurons but also motoneuron pools controlling biarticular muscles. It is unknown whether a preferred model can explain some particularities that fictive scratching (FS) in the cat presents. The first aim of this study was to investigate FS patterns considering the aiming and the rhythmic periods, and second, to examine the effects of serotonin (5HT) on and segmental inputs to FS. Methods: The experiments were carried out first in brain cortex-ablated cats (BCAC), then spinalized (SC), and for the midcollicular (MCC) preparation. Subjects were immobilized and the peripheral nerves were used to elicit the Monosynaptic reflex (MR), to modify the scratching patterns and for electroneurogram recordings. Results: In BCAC, FS was produced by pinna stimulation and, in some cases, by serotonin. The scratching aiming phase (AP) initiates with the activation of either flexor or extensor motoneurons. Serotonin application during the AP produced simultaneous extensor and flexor bursts. Furthermore, WAY 100635 (5HT1A antagonist) produced a brief burst in the tibialis anterior (TA) nerve, followed by a reduction in its electroneurogram (ENG), while the soleus ENG remained silent. In SC, rhythmic phase (RP) activity was recorded in the soleus motoneurons. Serotonin or WAY produced FS bouts. The electrical stimulation of Ia afferent fibers produced heteronymous MRes waxing and waning during the scratch cycle. In MCC, FS began with flexor activity. Electrical stimulation of either deep peroneus (DP) or superficial peroneus (SP) nerves increased the duration of the TA electroneurogram. Medial gastrocnemius (MG) stretching or MG nerve electrical stimulation produced a reduction in the TA electroneurogram and an initial MG extensor burst. MRes waxed and waned during the scratch cycle. Conclusion: Descending pathways and segmental afferent fibers, as well as 5-HT and WAY, can change the FS pattern. To our understanding, the half-center hypothesis is the most suitable for explaining the AP in MCC.

Role of the superior colliculus in the expression of acute and kindled audiogenic seizures in Wistar audiogenic rats.

PURPOSE: The role of the superior colliculus (SC) in seizure expression is controversial and appears to be dependent upon the epilepsy model. This study shows the effect of disconnection between SC deep layers and adjacent tissues in the expression of acute and kindling seizures. METHODS: Subcollicular transections, ablation of SC superficial and deep layers, and ablation of only the cerebral cortex were evaluated in the Wistar audiogenic rat (WAR) strain during acute and kindled audiogenic seizures. The audiogenic seizure kindling protocol started 4 days after surgeries, with two acoustic stimuli per day for 10 days. Acute audiogenic seizures were evaluated by a categorized seizure severity midbrain index (cSI) and kindled seizures by a severity limbic index (LI). RESULTS: All subcollicular transections reaching the deep layers of the SC abolished audiogenic seizures or significantly decreased cSI. In the unlesioned kindled group, a reciprocal relationship between limbic and brainstem pattern of seizures was seen. The increased number of stimuli provoked an audiogenic kindling phenomenon. Ablation of the entire SC (ablation group) or of the cerebral cortex only (ctx-operated group) hampered the acquisition of limbic behaviors. There was no difference in cSI and LI between the ctx-operated and ablation groups, but there was a difference between ctx-operated and the unlesioned kindled group. There was also no difference in cSI between SC deep layer transection and ablation groups. Results of histologic analyses were similar for acute and kindled audiogenic seizure groups. CONCLUSIONS: SC deep layers are involved in the expression of acute and kindled audiogenic seizure, and the cerebral cortex is essential for audiogenic kindling development.