Reviewer #1

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This manuscript describes some of characteristics of 5HT-evoked outward current in immature CA1 neurons dissociatod from rat hippocampus using nystatin perforated patch technique. In addicion, the study has focused on the possible signal transduction mechanism(s) involved in the somatic actions of 5-HT. In general. this is a very interesting work of contemporary interest, with adequate experimental methods used and reliable documentation. The investigators have established themselves in the field and the experiments presented are well-conceived and conducted. In my opinion, the paper contains sufficient new information to merit its publicatlon in the Journal of **** .

As two minor points, the authors should check references since some are missing from the bibliography (e.g. Kohler, 1984) and others should be checked for correctness. In addition, the paper will need editorial assistance with English language .

Reviewer #2

Review of 'Title'. By authors.

This is a good piece of work describing a new type of 5-HT response in hippocampal neurons. The finding of a 5-HT2 receptor gating a K channel is novel. The coupling via phospholipase C, IP3, and intracellular Ca stores is novel for 5-HT. The experiments upon which these conclusions are based are well executed and convincing. This study appears also to be the first use of the nystatin technique to examine 5-HT responses in the hippocampus.

One cause for concern is that this type of response has not been described previously for 5-HT in hippocampal neurons, despite the fact that a number of laboratories have published studies with methods that should have revealed it. Not only did Andrade and Nicoll (1987) and Colino and Halliwell (1987) fail to see such a response, but so did Yakel et al, J. Neurosci. 8, 1 273, 1988. This later study was with the patch clamp in cultured embryonic mouse hippocampus, under conditions closer to those employed by the present authors. One must therefore ask for a more critical discussion of the experimental conditions, including the possibility that the enzymatic treatment produced artifacts.

The concern is amplified by the fact that 5-HT2 receptors are generally thought to be coupled to adenylate cyclase rather than phospholipase C. The authors could strengthen their position by finding a biochemical study in the literature showing that 5-HT2 receptors are coupled to this other enzyme.

The pharmacology showing that the authors are studying a 5-HT2 receptor is being published elsewhere. Given the novelty and relevance of the results, and the fact that this paper is in press, a copy should have been made available to the reviewers.

The biphasic response in Fig. 6C is difficult to understand. Was this common? How do the authors explain it?

While the transduction mechanism described here is novel for 5-HT, the mechanism has been shown for other ligands and cells. In particular, Higashida and Brown, Nature 323, 333, 1986 showed that bradykinin has a similar effect in neuroblastomaXglioma hybrid cells .

There are a large number of errors of language, some of which I corrected in my copy which I have returned to the editors.