TABLE 1

Frequency of occurrence of subtypes of VMN neurons in DR and DIO-prone rats that respond to changes in extracellular glucose

DR rats
DIO-prone rats
PrimaryPresynaptic
Decreased glucose
 Excited3 (3); GI14 (14); PED3 (6)
 Inhibited14 (14); GE03 (6)
Increased glucose
 Excited08 (9); PER1 (3)
 Inhibited010 (11); PIR1 (3)
  • Data are n subtype (% VMN neurons that subtype represents in DR and DIO-prone rats). A total of 100 neurons in DR rats and 53 neurons in DIO rats were tested for a response to a decrease in extracellular glucose levels from 2.5 or 5 to 0.1 mmol/l. Altogether, 92 neurons in DR rats and 36 neurons in DIO rats were tested for a response to an increase in extracellular glucose levels from 2.5 to 5 or 10 mmol/l. VMN neurons in DR rats are primarily glucosensing if the response to glucose is postsynaptic. Presynaptic refers to neurons in DR rats in which the observed changes were abolished under conditions of high Mg2+ and low Ca2+, which remove presynaptic transmission. Determination of primary versus presynaptic glucose responses in DIO rats was impossible because of either high steady- state activity or low occurrence. In DR rats, VMN neurons that were directly excited by decreased glucose are referred to as GI neurons, whereas those that were directly inhibited are GE neurons. VMN neurons that were presynaptically excited by decreased glucose are referred to as PED neurons. VMN PER and PIR neurons are presynaptically excited or inhibited, respectively, when extracellular glucose was raised.