After reading the first few sentences of the 2nd paragraph, I basically said "screw it. Let's just look at the structure of the passage." I think that the LSAT likes to trick us, ESPECIALLY with the science passages, into thinking that the details actually matter. With a dense passage like this, I try not to worry about the little details because, if need be, I can always go back to the relevant points and re-read because I'll at least have a general idea about where to find the details.
Here is what I took note of:
Key sentence: "It has now become clear, however, that other hormones, in addition to their recognized influence on biological functions, can affect behavior. Specifically, peptide and steroid hormones...play an important role" (6-12)
(1) A decrease in plasma osmolality... (line 37)
(2) An increase in plasma osmolality...(line 44-45)
That is basically all I took note of. The author really only put an opinionated sentence from (6-12). Everything else is just describing a process. Therefore, I will have what I need to go into the "main point" question and I'll be able to find the details later.