A monosynaptic connection between baroinhibited neurons in the RVLM and IML in Sprague-Dawley rats

To date, few studies have examined the relationship between the firing rate of neurons in the rostral ventrolateral medulla (RVLM) and neurons in the intermediolateral cell column (IML) of the spinal cord. In 19 Sprague-Dawley rats, the relationship between 20 pairs of baroinhibited RVLM and IML units was analyzed by cross-correlation. Three criteria were applied before acceptance that the firing rate of a pair of neurons was correlated. First, at an appropriate latency following the firing of an RVLM neuron, as judged from previous studies (4-200 ms), the peak in the firing rate of an IML neuron was approximately double that of the averaged surrounding bin counts. Secondly, the peak grew steadily in the examined period. Thirdly, the peak was restricted to a 1-ms bin. With this approach, a correlation was found between RVLM and IML neurons in 3 pairs in all. In 2 pairs, a correlation was found at basal arterial pressure (AP). When AP was decreased using a caval snare, a correlation was demonstrated in a further pair. A possible potentiation of synaptic strength during hypotensive stimuli is discussed.