The pineal gland of the Mongolian gerbil: nocturnal increase of electrical activity.

Extracellular single unit recordings were made during day- and nighttime from spontaneously active pineal gland cells in male Mongolian gerbils. Units exhibited an irregular firing pattern. Discharge frequencies ranged from 0.1 to 8.5 Hz and showed distinct time-dependent differences. During daytime, mean firing frequencies were in the range of 1 Hz and increased to 2 Hz in the early dark period, reaching a peak (ca. 5 Hz) in the middle of the night, followed by a decrease to 2 Hz in late night. The results of this first report on pineal electrical activity in Mongolian gerbils are discussed in comparison to those obtained from rat, guinea pig and golden hamster.