EXTRACELLULAR GLUTAMATE INCREASES IN ROSTRAL VENTROLATERAL MEDULLA DURING STATIC MUSCLE-CONTRACTION

The ventrolateral medulla is an important site involved in increases i n arterial pressure and heart rate during static muscle contraction. G lutamate, an excitatory amino acid neurotransmitter, appears to play a role in mediating these responses. We measured glutamate concentratio n in the extracellular fluid of the rostral ventrolateral medulla duri ng static muscle contraction in anesthetized rats. A 2-min tibial nerv e stimulation-evoked muscle contraction increased blood pressure by 30 +/- 4 mmHg and heart rate by 32 +/- 4 bpm. Extracellular glutamate in the rostral ventrolateral medulla also increased from 9 +/- 1 pmol/4 mu l to 14 +/- 1 pmol/4 mu l. Results were repeatable over two subsequ ent contractions. Tibial nerve stimulation following neuromuscular blo ck ade did not elicit changes in blood pressure, heart rate or extrace llular fluid glutamate. Data demonstrate that muscle contraction incre ases extracellular fluid concentration of glutamate in the rostral ven trolateral medulla, suggesting that rostral ventrolateral medullary gl utamate release is a neurochemical change associated with cardiovascul ar responses during static muscle contraction.