Shri Krishna mentions about Kundalini shakti & awakening in The Bhagavad Geeta
I shall now declare unto thee, O Best of the Bharatas (Arjuna), the path, traversing which at the time of death, yogis attain freedom; and also the path wherein there is rebirth. Fire, light, daytime, the bright half of the lunar month, the six months of the northern course of the sun—pursuing this path at the time of departure, the knowers of God go to God. —The Bhagavad Gita VIII:23-24
These mysterious stanzas, woefully misinterpreted by nearly all commentators, in reality contain symbolic references to the science of yoga.
They describe the opening of the spiritual eye, the awakening of the cerebrospinal centers, and the ascension of life force and consciousness through them to Cosmic Consciousness and liberation in Spirit of the yogi who follows the “way of light.”
And, on the contrary, they describe also the descension or return to body consciousness or rebirth of those yet unable to open fully all the cerebrospinal doors that lead ultimately to Spirit.
Liberation, freeing the soul from the physical, astral, and causal bodies, is the purport of these verses.
The ponderous scriptures of the rishis have defined in veiled terms the labyrinth of the soul’s descension and ascension. Krishna has here stated this portion of the yoga science succinctly for the comprehending Arjuna—the advanced yogi-devotee.
The rudiments are as follows: Stanza 24 states that the yogi who attains liberation must follow the path of “fire.” Here “fire” means the life energy, the kundalini power.
The devotee’s first scientific step toward emancipation is to gain control of his life force. In ordinary men the course of prana is downward, “the way of darkness,” flowing from the brain to the sensory nerves and the countless cells of the body. This dispersion and diffusion of life energy reveal to human consciousness the material world.
In the successful yogi, on the other hand, the course of prana is upward, “the way of light.” By yoga he reverses the direction of the flow and is able to concentrate the whole of his life force within the brain, in the “sun” of Cosmic Consciousness. In this way God is revealed.
The “sun” of Cosmic Consciousness is the Supreme Source of life and intelligence in the body, with Its abode in the seventh or highest spiritual center, in the cerebrum, in the thousand-petaled lotus—a sunburst as of a thousand suns.
All life and faculties in the body evolve from this powerhouse of luminosity through its projected rays of the spiritual eye. “Light” in stanza 24 refers to the divine eye in the forehead, whose awakening enables the yogi to say with Christ: “I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life.” (…)
The “six months” are the six spinal centers, the coccygeal to the spiritual eye. Thus, the “six months of the northern course of the sun” refers to the six periods of spiritual perceptions in these centers as consciousness and life (descended from the “sun” of Cosmic Consciousness into the body) are reversed to flow upward, “north,” to their Supreme Source in the cerebrum.
What transpires as the yogi moves along this “way of light” is a veritably intricate transition of his life and consciousness through the spiritual eye: First, life and consciousness move upward through the physical spine and brain, freeing the yogi from the physical body; then transition through the three astral spines of light (sushumna, vajra, chitra), freeing the yogi from the astral body; and, lastly, ascension through the causal “spine” of consciousness (brahmanadi), whereby the soul is liberated in Spirit.
At death, the soul of the successful yogi, following this path, rises majestically, unencumbered, from the revolving cycles of obligatory rebirths.
(Chapter VIII, God Talks With Arjuna: The Bhagavad Gita by Paramahansa Yogananda) — Read more at: http://www.yogananda.com.au/pyr/pyr_kundalini1.html