Q:

How do I double-space my abstract in LaTeX?

I'm finishing up my undergrad thesis, and I have to double-space my abstract. I tried using \begin{doublespace} and \doublespacing, but neither have worked, I assume because the abstract environment is different than for the rest of the document. Any ideas/suggestions?

A:

Based on Paulo Cereda's suggestion (And the fact I just wrote up a thesis with an abstract using that package, though I didn't double space the abstract), I threw together an example of how this works. 
\documentclass{article}
\usepackage{setspace}   %Allows double spacing with the \doublespacing command

\begin{document}
\begin{abstract}
\doublespacing
\noindent Hyperpolarization-activated and cyclic nucleotide-modulated (HCN) channels control cell membrane excitability in the human heart and central nervous system. 
The HCN channels have been shown to be more sensitive to cAMP then to cGMP.
One of the most significant differences between the two ligands is that cAMP binds in the \textit{anti}-conformation, 
with the base ``over'' the ribose, while cGMP binds in the \textit{syn}-conformation, with the base ``away'' from the ribose.
This suggests that the \textit{anti} vs.\ \textit{syn} conformational selection is a key aspect of the cAMP vs.\ cGMP selectivity in HCN. 
Our goal was to dissect the structural determinants of the \textit{anti} vs.\ \textit{syn} conformational selection. 
For this purpose, we have investigated cIMP, a cyclic nucleotide analogue, and the I636D HCN point-mutation, targeting the ligand-binding regions by NMR spectroscopy. 

We have shown that in solution the HCN\ I636D construct binds to cAMP and cGMP in a similar manner to wild-type HCN2, without the reversal of selectivity previously shown by Zhou and Siegelbaum.
Cyclic IMP has been shown to bind to HCN\ far more weakly then either cAMP or cGMP, indicating that the unfunctionalized 2-position of cAMP is not the reason for its stronger binding then cGMP.
Solution NMR based methods have also allowed the direct determination of binding conformation  (i.e.\ \textit{anti-} vs.\ \textit{syn-}) in cGMP bound to the I636D mutant, and shows promise in finding the conformation of further species.  
\end{abstract}
\end{document}

Note: I had to remove some macros from my thesis to get it more minimal, so some details are missing from the text, which introduced some errors. Just pretend it is a lipsum. (Edit: By which I mean, the text is no longer 100% accurate, not that there are LaTeX errors)

A:

 Don't use this solution, use setspace instead.
For completeness sake, I'm adding another solution. Avoid using it at all costs.
You can also use \linespread. The parameter is a factor. Our friends lockstep and Werner provided great answers to this subject in the Why is the linespread factor as it is? question.
By simply calling \linespread{1.6}, nothing happens. The explanation is provided in the great UK List of
TeX Frequently Asked Questions:

The command \linespread{factor} is supposed to multiply the current \baselineskip by ; but, to all appearances, it doesn’t.
In fact, the command is equivalent to \renewcommand{\baselinestretch}{factor}: written that way, it somehow feels less surprising that the effect isn’t immediate. The \baselinestretch factor is only used when a font is selected; a mere change of \baselinestretch doesn’t change the font, any more than does the command \fontsize{size}{baselineskip} — you have to follow either command with \selectfont.

Then you can use the following code in your abstract environment.
\begin{abstract}
\linespread{1.6}\selectfont
Text comes here...
\end{abstract}

The other parts the document remain untouched because this change happens inside an environment.
Again, don't use this solution, prefer the setspace package. :)

