Further evidence for cholinergic habenulo-interpeduncular neurons: pharmacologic and functional characteristics

Placement of high frequency lesions in the medial habenular area results in a large depletion of acetylcholine (ACh) levels, choline acetyltransferase (ChAc) activity, and high affinity choline uptake in the interpeduncular nucleus area (IPN) at 1, 3 and 7 days post-lesion. Areas adjacent to the IPN did not have a reduction in ChAc activity. The reduction in high affinity choline uptake was selective in that there was no change in the uptake of L-[3H]tyrosine or L-[3H]glutamic acid. Unlike the cholinergic septal-hippocampal neurons, there was no rise in ACh levels in the IPN 1 h after placement of lesion, or 30 min after administration of pentobarbital. While the IPN probably has a much denser cholinergic innervation than the hippocampus (as evidenced by much higher ACh levels, ChAc activity and choline uptake levels), it has only one-fourth as many [3H]QNB binding sites (a measure of cholinergic muscarinic receptors). This, some of the habenulo-interpeduncular neurons are probably cholinergic, and they may have pharmacologic and functional differences compared to the septal-hippocampal neurons.