Gg. Kinney et al., MEDIAL SEPTAL UNIT FIRING CHARACTERISTICS FOLLOWING INJECTIONS OF 8-OH-DPAT INTO THE MEDIAN RAPHE NUCLEUS, Brain research, 708(1-2), 1996, pp. 116-122
Extracellular single-unit recording techniques were used to examine th
e firing characteristics of neurons in the medial septum/diagonal band
of Broca complex (MS/DB) following injections of the 5-HT1A agonist,
8-OH-DPAT, into the median raphe nucleus (MRN) of urethane-anesthetize
d rats. It had previously been shown that MRN injections of 8-OH-DPAT
product hippocampal theta rhythm. Injections of 8-OH-DPAT into the MRN
produced a change in firing characteristics of MS/DB neurons from an
irregular discharge to a pattern of rhythmical bursting in synchrony w
ith hippocampal theta rhythm. Cross-correlational and coherence analys
es demonstrated that the rhythmical firing pattern of MS/DB neurons st
rongly correlated with rhythmical fluctuations in the hippocampal EEG
during periods of hippocampal theta produced by 8-OH-DPAT injections,
but not during baseline conditions (i.e. hippocampal desynchronization
). The results suggest that MRN control of the hippocampal EEG is modu
lated by the MS/DB. Serotonergic projections from the MRN to the MS/DB
may normally act to inhibit the rhythmical bursting of MS/DB neurons,
thereby producing hippocampal desynchronization. Suppression of MRN 5
-HT neurons by MRN injections of 8-OH-DPAT would disinhibit MS/DB neur
ons, allowing them to burst rhythmically and thereby produce hippocamp
al theta rhythm.