Spinal cord excitability is not influenced by elevated blood lactate levels

Abstract

The aim of the present study was to examine the association of high blood lactate levels, induced with a maximal cycling or with an intravenous infusion, with spinal cord excitability. The study was carried out on 17 male athletes; all the subjects performed a maximal cycling test on a mechanically braked cycloergometer, while 6 of them were submitted to the intravenous infusion of a lactate solution (3 mg/kg in 1 min). Before the exercise or the injection, also at the end as well as 5 and 10 min after the conclusion, venous blood lactate was measured and excitability of the spinal α-motoneurons was evaluated by using the H reflex technique. In both experimental conditions, it has been observed that an exhaustive exercise is associated with a strong increase of blood lactate (but not of blood glucose) and with a significant reduction of spinal excitability. Since a similar augment of blood lactate induced by an intravenous infusion, in subjects not performing any exercise, is not associated with significant changes of spinal excitability, it can be concluded that the increase of blood lactate levels during a maximal exercise is not per se capable of modifying the excitability of spinal α-motoneurons.

Attentional processes during submaximal exercises

“…This enhancement of M1 excitability strongly correlates with the increase of blood lactate and in the same study ) a similar effect on the M1 hand area was also observed when increasing the blood lactate levels by an intravenous infusion in resting participants. The same group suggested that lactate acts at the cortical level since they observed that the improvements in M1 excitability is not associated with changes of excitability of spinal (Coco et al 2011) or brain stem (Coco et al 2013a). Moreover, it has been recently observed in vitro that lactate may promote astroglial brain-derived neurotrophic factor expression related to an increase in heat shock protein 70 in adverse situations (Coco et al 2013b).…”

Effects of an Exhaustive Exercise on Motor Skill Learning and on the Excitability of Primary Motor Cortex and Supplementary Motor Area

“… 4 , 5 It has also been suggested that in the brain, in particular in conditions of altered energy production, such as anoxia or hypoglycemia, lactate is the energetic metabolite used for sustaining glutamatergic synaptic activity. 6 However, it has been observed that an increase of blood lactate, induced by an exhaustive exercise or an intravenous infusion, is associated with a worsening of attentional processes, 7 an improvement of excitability of primary motor cortex, 8 without significant modifications of spinal 9 and brainstem 10 excitability. Furthermore, experiment carried out with visual-evoked potentials 11 and somatosensory-evoked potentials 12 have shown that increases of blood lactate are associated, in both cases, with that an improvement in the conduction time between the periphery and the primary sensory areas and the worsening of intracortical communication between primary areas and additional cortical regions.…”

Exhaustive Exercise Alters Thinking Times in a Tower of London Task in a Time-Dependent Manner

“…In terms of frontal lobe functioning, elevated lactate levels seem to play a crucial, region-specific role. While some studies reported that increased lactate levels are associated with improved excitability in the primary motor cortex (Coco et al, 2010, 2014), other investigations stated contrary results for the frontal cortex as well as for brainstem and spinal cord excitability (Coco et al, 2009, 2011, 2013). Regarding the lactate uptake of the CNS from a biochemical point of view, a strong increase might lead to metabolic irritations through a decrease in pH values, which is driven by the co-transport of protons by the monocarboxylate transporter MCT1 (blood-brain barrier) as well as MCT2 and MCT4 within the CNS (Bergersen, 2015).…”