Descending control of electroreception. II. Properties of nucleus praeeminentialis neurons projecting directly to the electrosensory lateral line lobe.

The nucleus praeeminentialis projects to the electrosensory lateral line lobe via 2 distinct pathways. Neurons that project to the posterior eminentia granularis and therefore influence the electrosensory lateral line lobe indirectly are described in the preceding report. This report describes the physiological properties and anatomical characteristics, revealed with Lucifer yellow staining, of n. praeeminentialis neurons that project directly to the ventral molecular layer of the electrosensory lateral line lobe. The neurons studied were the stellate cells described by Sas and Maler (1983), and we found 2 physiological subtypes of these. These neurons typically had no spontaneous activity, but responded vigorously to either increased electric organ discharge amplitude on the contralateral side of the body (ST-E cells) or to decreased amplitude (ST-I cells). These neurons also responded to low-frequency sinusoidal electric organ discharge amplitude modulations (AM) but were inhibited by AMs having frequencies greater than about 16 Hz. These stellate neurons were unable to encode information about long-term changes in electric organ discharge amplitude, but they responded very well to moving electrolocation targets. The relatively long response latency of these neurons suggests that they receive inputs from higher centers in addition to those from the electrosensory lateral line lobe. It is suggested that these cells alter the sensitivity of restricted populations of output cells in the electrosensory lateral line lobe and process temporally and spatially restricted stimuli. They may act to increase the intensity of the neural representation of important stimuli.