The effects of electrical stimulation of the Al noradrenergic cell group on the extracellular activity of medial preoptic-medial septal (MPO-S) neurons were studied in ovariectomized (OVX) female rats under different hormonal conditions [estrogen and progesterone (E-P)-primed or unprimed] via conventional electrophysiological techniques. In addition, MPO-S neurons responding to the Al noradrenergic cell group stimulation were characterized by examining their connections with the arcuate nucleus/median eminence (ARC/ME). With respect to stimulation of the Al noradrenergic cell group, a large proportion of MPO-S neurons exhibited one of the following three types of orthodromic responses: orthodromic excitation (OD + ), orthodromic inhibition (OD-), or complex orthodromic response (OD comp). The predominant type of response was OD +. Although E-P-priming did not change the relative proportion of neurons displaying a specific type of orthodromic response, it did increase the overall percentage of MPO-S neurons orthodromically responding to Al stimulation (39% of MPO-S neurons responded to Al stimulation in the E-P-primed group whereas only 25% of the neurons did so in the unprimed group). Neurons responsive to Al stimulation were more likely to respond orthodromically to ARC/ME stimulation than were those neurons which were unresponsive to Al stimulation. About one fifth of MPO-S neurons identified as projecting to the ARC/ME [putative luteinizing hormone-releasing hormone (LHRH) neurons] orthodromically responded to Al stimulation. The predominant type of response was OD + . The present study indicates that Al noradrenergic input to MPO-S neurons is predominantly excitatory. Furthermore, the findings that (1) the proportion of neurons which responded to Al stimulation was increased by E-P-priming, a treatment used to induce a surge in luteinizing hormone (LH) secretion in an OVX rat, (2) the neurons responding to Al stimulation had a tendency to receive input from the ARC/ME, a brain site intimately involved in the control of LH release, and (3) the activity of putative LHRH neurons was able to be affected by Al stimulation suggest that Al input to MPO-S area may be involved in the control of LH secretion.