Question: From which seasons are there gag reels?
About the article "The Big Bang Theory", section "DVD/Blu-ray releases".

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Sony Pictures Home Entertainment released all 5 seasons of "NewsRadio" on DVD in Region 1 between 2005–2007.
Each set includes multiple audio commentaries with creator Paul Simms, the writers and actors.
The DVD sets also include "special features" such as "gag reels" and other featurettes.
As of 2014, these releases have been discontinued and are out of print.
On August 27, 2013, it was announced that Mill Creek Entertainment had acquired the rights to various television series from the Sony Pictures library including Newsradio.
On February 20, 2014, it was announced that they will be re-releasing the first two seasons on DVD on April 1, 2014. 
Often manufactured from recycled plastic, these reels are environmentally friendly and used for lighter weight cables. 
The proliferation of out-takes/gag reels/blooper reels, especially on recent DVD releases, has received mixed response by actors and directors.
While many do not mind the extra publicity offered by such material being shown to the public and others simply enjoy seeing the mistakes, other actors complain that out-takes are demeaning to themselves and/or the craft and refuse to allow them to be made public.
Director Hal Ashby's decision to include a blooper reel of star Peter Sellers in his 1979 film "Being There", for example, is sometimes blamed for Sellers' failure to win that year's Academy Award for Best Actor (for which he was nominated).
Sellers had reportedly urged Ashby not to include the outtakes in the final edit of the film, to no avail.
Among his other issues with "Star Trek"'s producer Gene Roddenberry, Leonard Nimoy was not happy that Roddenberry showed the show's blooper reels to fans at conventions in the early 1970s.
He felt actors needed to be free to make mistakes without expecting that they would be shown to the public, and wrote a letter to Roddenberry asking him to stop.
Roddenberry's answer was to send Nimoy a blooper reel of his own should he have wished to show it at conventions. 
Three types of reels are commonly used in bowfishing: Hand-wrap, spincast, and retriever.
Hand-wrap reels are the simplest reels; they consist of a circular spool that line is wrapped onto by hand and then secured in a line holding slot.
When the arrow is shot the line comes free from the line holder and feeds off the spool.
Fish are caught by pulling the line in hand over hand; hand-wrap reels are the least effective at fighting arrowed fish, but they can be used in conjunction with a float system to shoot and fight large trophy fish.
Retriever reels have a "bottle" which holds the line in place.
When shot the line comes out either until the shot goes too far and the line runs out or the hunter pushes down a stopping device which can be used to keep a fish from traveling out too far.
Some retriever reels have slots cut in them and are known as slotted retriever reels.
They are more commonly used for alligator, alligator gar, shark and other big game that will take more time to chase down than smaller game fish. 
"Gags" — silly pranks that are reflective of the slapstick humor found in classic cartoons, were the tools used to destroy the Cogs in Cog battles.
There were a total of seven gag tracks: toon-up, trap, lure, sound, throw, squirt, and drop.
Each gag track consisted of seven gags.
Players were only allowed to have six gag tracks, two of which were given at the start of the game.
Each gag track had its own unique properties and powers.
The properties of every gag track could have been used with each other in Cog battles to the player’s advantage or disadvantage to encourage teamwork.
Gag tracks were obtained by completing a number of Toontasks to train for the selected track.