Hind limb motoneurons activity during fictive locomotion or scratching induced by pinna stimulation, serotonin, or glutamic acid in brain cortex-ablated cats

Abstract

In brain cortex‐ablated cats (BCAC), hind limb motoneurons activity patterns were studied during fictive locomotion (FL) or fictive scratching (FS) induced by pinna stimulation. In order to study motoneurons excitability: heteronymous monosynaptic reflex (HeMR), intracellular recording, and individual Ia afferent fiber antidromic activity (AA) were analyzed. The intraspinal cord microinjections of serotonin or glutamic acid effects were made to study their influence in FL or FS. During FS, HeMR amplitude in extensor and bifunctional motoneurons increased prior to or during the respective electroneurogram (ENG). In soleus (SOL) motoneurons were reduced during the scratch cycle (SC). AA in medial gastrocnemius (MG) Ia afferent individual fibers of L6‐L7 dorsal roots did not occur during FS. Flexor digitorum longus (FDL) and MG motoneurons fired with doublets during the FS bursting activity, motoneuron membrane potential from some posterior biceps (PB) motoneurons exhibits a depolarization in relation to the PB (ENG). It changed to a locomotor drive potential in relation to one of the double ENG, PB bursts. In FDL and semitendinosus (ST) motoneurons, the membrane potential was depolarized during FS, but it did not change during FL. Glutamic acid injected in the L3‐L4 spinal cord segment favored the transition from FS to FL. During FL, glutamic acid produces a duration increase of extensors ENGs. Serotonin increases the ENG amplitude in extensor motoneurons, as well as the duration of scratching episodes. It did not change the SC duration. Segregation and motoneurons excitability could be regulated by the rhythmic generator and the pattern generator of the central pattern generator.

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

“…In this study, 5HT neuromodulatory mechanisms were described for the first time in cat scratching behavior, particularly during the AP. Increased extensor motoneuron's excitability through serotoninergic pathways could favor synaptic effects in the extensor motoneurons (Duenas-Jimenez et al, 2017). This 5HT-mediated excitability increase was also seen in studies addressing firing properties, depolarization, hyperpolarization, plateau potentials, and neuronal recruitment during the cat stretch reflex (Hounsgaard et al, 1988).…”

“…In brain cortex-ablated cats (BCAC), the AP in FS could initiate with either extensor or flexor tonic activity and is followed by the RP (Duenas-Jimenez et al, 2017). Interestingly, the AP in most midcollicular cats (MCC) starts with flexor tonic activity (Berkinblit et al, 1978).…”

“…In BCAC, the heteronymous monosynaptic reflex (HeMR) produced by Ia afferent fibers acting in motoneurons of the same joint has been previously analyzed (Duenas-Jimenez et al, 2017). However, these reflexes were not fully analyzed among the Ia afferent fibers and motoneurons innervating the hindlimb muscles acting in different joints.…”

Synergistic interaction between sensory inputs and propriospinal signalling underlying quadrupedal locomotion

“…The same phenomenon was also described in the cat at the beginning of motoneuronal burst discharges during actual and fictive locomotion, as well as during fictive scratching (Zajac & Young, 1980; Duenas‐Jimenez et al . 2017). High frequency impulse doublets occurring in motoneurons at the beginning of a muscle contraction are associated with a non‐linear increase in the contractile (output) strength produced by the muscle fibers.…”

Contributions of h- and Na+/K+pump currents to the generation of episodic and continuous rhythmic activities

“…Rapid transitions between swimming and crawling can be facilitated by sensory stimulation, which can be biased through hyperpolarization or depolarization of a single neuron in the circuit (Briggman et al, 2005). In line with this, stimulation of the pina in cortex-ablated cats can elicit either fictive scratch or fictive locomotion, with a bias toward locomotion when serotonin or glutamic acid is applied to the spinal cord (Duenas-Jimenez et al, 2017). These examples of rapid switching may be facilitated by networks operating within a multistable zone of parameter space.…”