A comparison of the effects of eserine sulfate on the activity of medullary raphe neurons in the anesthetized rabbit and rat

ABSTRACT

1. Medullary raphe neurons are involved in the control of sympathetic activity during desynchronized sleep (DS). Eserine sulfate induces a state with the somatic and visceral signs of DS in decerebrate animals. The rabbit and rat display diverse hemodynamic patterns during DS. 2. To determine whether eserine sulfate provokes different responses in the medullary raphe neuron population of these different species, the drug (100 mg/kg, i.v.) was administered to urethane-anesthetized (1.2 g/kg, i.v.) rabbits (1.5-3.0 kg) and rats (Wistar, 260-310 g). 3. Extracellular activity was recorded from 66 neurons in 30 rats. Cholinergic stimulation provoked an increase in discharge rate (DR) in 45 neurons (68), a decrease in 8 neurons (12) and no change in 13 neurons (20). Recordings were obtained from 30 neurons in 11 rabbits. Stimulation of these cells provoked an increase in DR in 17 neurons (57), a decrease in DR in 7 neurons (23) and no change in 6 neurons (20). Interspike interval and auto-correlation analysis was performed on 28 rat and rabbit neurons. No significant difference was found between the rat and the rabbit with respect to the number of the neurons which were either inhibited or excited by cholinergic stimulation (P > 0.05). Similarly, unit response to eserine was not related to whether the unit displayed regular or irregular DR. 4. Therefore, we suggest that the diverse hemodynamic patterns during DS and the distinct cardiovascular responses to raphe nuclei stimulation are not due to differences in the organization of the raphe nuclei themselves but to differences in their axonal projections or in the postsynaptic receptors activated in the intermediolateral cell column or other postsynaptic targets.