Velar Negatives

As well as negatives derived from PIE *ne and *meh1, there appear to
be negatives in many IE languages which have a velar root; e.g.
Latin - haud
Greek - ouk
German - kein
Dutch - geen
Icelandic - ekki
Gothic - ains-hun
Does anyone know the etymology of these forms? Do they all derive
from a common PIE negative particle? Did this root occur at all in
Old English?

Brian