How fast do inhaled drugs reach the brain?

[MerryMagdalen]

<hijack>

When the IV and inhalation route are just not enough, some addicts have tried injecting directly into the carotid artery, to get the stuff to the brain faster. (ETA: The carotid feeds the brain)

Wait, what now? Every addict I’ve ever known knows artery=bad. And doing an LP? Who are these people? (We do have one lady that likes to check into the hospital and then walk out with her PICC still in, but that’s pretty mild.)

I believe you, because I know addicts can be crazy like that but…wow. I would like to read more.

</hijack>

[Santo_Rugger]

@matt

Well, that’s an answer! Assuming we’re talking about a drug that affects the brain, the transport time of something that kicks in before you can breath out is a couple of heartbeats or less… or else it works by a different mechanism.

Ever seen anybody smoke crack?

[Staggerlee]

@CC

Waaaaaait a minute. Olfactory nerves respond to chemical stimuli that are then translated into electrical signals that go to the brain. How can the effects of a chemical that works in the brain be transmitted by electrical signals? If oxytocin is administered nasally, I believe it still is being transmitted via the circulatory system. Where’s Doc Quagdop?

Chemicals such as cocaine are absorbed through the mucas membrane of the sinuses, and from there straight to the brain (afaik) so you don’t need to smell the substance to absorb it.

[Szlater]

@Staggerlee

Chemicals such as cocaine are absorbed through the mucas membrane of the sinuses, and from there straight to the brain (afaik) so you don’t need to smell the substance to absorb it.

Presumably substances enter the bloodstream through the mucus membrane, rather than some other mechanism? Does blood from there go directly to the brain, or does it return to the heart first?

[matt]

@Szlater

I’ve been looking for some info on PET scans that use an inhaled radiolabelled tracer, and how long it takes for the tracer to show up in the brain (…snip…) Maybe someone with better google-fu will find something

It’s a hard subject to Google, the results are flooded with medical papers that you have to pay to read, although the abstracts are sometimes useful. But something that got my attention was this article regarding CT scans - you have to get the timing just right to prevent the scanner from “outrunning” the contrast agent as it moves from the aorta down into the legs and feet:

http://www.medicexchange.com/mall/departmentpage.cfm/MedicExchangeUSA/_0/361/departments-contentview

It’s a little hard to interpret, and I’m fairly sure it contains some errors as well - the bit on scan speeds doesn’t make sense. But it does give some speeds of travel for the contrast agent along the arteries - 33 mm/sec to 177mm/sec. It is discussing patients with “peripheral arterial occlusion disease” however, where “the bolus transit down the peripheral territory can be substantially delayed”. Presumably, transport speeds in healthy patients are towards the higher end of the range.

@jimm

I think someone here needs to huff some 1-1-1 tricholroethane*. About two seconds, I reckon, from my ill-spent youth

Which according to wiki is a CNS depressant, which suggests it needs to reach the brain to have an effect. Thinking about it, amyl nitrite is similarly rapid. It’s a vasodilator, so I have no idea if it needs to reach the brain to work, or if it affects the smooth muscle in the walls of blood vessels directly as it passes down them. Two seconds is at least consistent with the faster of the transit times listed above.

@Pygmy Rugger

Ever seen anybody smoke crack?

Not yet! Do tell…

[CC]

@Staggerlee

Chemicals such as cocaine are absorbed through the mucas membrane of the sinuses, and from there straight to the brain (afaik) so you don’t need to smell the substance to absorb it.

Nope. You and I agree - smelling it is not a route to the brain. But once it’s absorbed by the mucous membranes, it then passes into the circulatory system, where it is taken back to the heart, to the lungs, to the heart and THEN to the brain. May take only 20 - 30 seconds, but it’s not going directly to the brain, regardless of how close it is. xo, C.

[vetbridge]

Interesting tangent. There is now a short acting insulin product designed to be snorted:
http://www.exubera.com/content/con_index.jsp?setShowOn=../content/con_index.jsp&setShowHighlightOn=../content/con_index.jsp

[Enola_Straight]

re. the OP…at least two heartbeats: One heartbeat to move blood from the lungs to the heart, and another beat to move the blood from the heart to the brain.

[CC]

@Enola Straight

re. the OP…at least two heartbeats: One heartbeat to move blood from the lungs to the heart, and another beat to move the blood from the heart to the brain.

That’s pretty fast, don’t you think? One diastole and one systole to receive and pump what’s coming in and what’s on the way out, and then just one more? I’m guessing that’s pushing it. “Guessing” being the operative term. Do we have any evidence? Cite? Source?

[phouka]

@CC

Waaaaaait a minute. Olfactory nerves respond to chemical stimuli that are then translated into electrical signals that go to the brain. How can the effects of a chemical that works in the brain be transmitted by electrical signals? If oxytocin is administered nasally, I believe it still is being transmitted via the circulatory system. Where’s Doc Quagdop?

I stand corrected. Previous reading on my part lead me to believe that oxytocin crossed into the brain via the olfactory nerve and bulb. Rereading wikipedia’s entry, I found:

Nasally-administered oxytocin has also been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses).[12] There is no conclusive evidence for access of oxytocin to the brain through intranasal administration, however.

Oxytocin does not cross the blood-brain barrier. Oxytocin created in the pituitary gland does not have an effect on the brain. Also:

Oxytocin given intravenously does not enter the brain in significant quantities - it is excluded from the brain by the blood-brain barrier. Drugs administered by nasal spray are thought to have better access to the CNS.

There appears to be some unknown quality about how intranasally administered oxytocin reaches the brain. It does, as there is a quantifiable effect. It doesn’t get there via the circulatory system, as IV oxytocin never makes it to the brain. Perhaps the molecule is not transferred directly to the brain by the olfactory nerve but sparks a series of neural signals that cause a proportionate secretion of oxytocin by the brain itself.

Dunno.

Looks like there’s a master’s or doctoral thesis in there for someone to figure out.

[CC]

@phouka

Looks like there’s a master’s or doctoral thesis in there for someone to figure out.

Boy, ya got THAT right. I do know that one quirk of the B/B barrier is that it is not particularly effective in the thalamus. It is one place that infection can move from the body to the brain. I wonder if it is also the locus or receptor of the vector for the oxytocin effect, if there is, in fact, such a thing. Moving out on a big limb here. xo, C.

[Qadgop_the_Mercotan]

@CC

Nope. You and I agree - smelling it is not a route to the brain.

Smelling it is actually the most direct route to the brain that there is.

The first cranial nerve, the olfactory nerve, is really just a modified portion of brain tissue extending over the cribriform plate in the ethmoid bone. The olfactory nerve feeds into the limbic system and the cerebrum itself, rather than the brainstem.

Olfactory nerve

http://mywebpages.comcast.net/epollak/PSY255_pix/Olfactory_bulb_netter.JPG

So if receptors for the substance exist in the olfactory nerve, they’ll be directly stimulated and respond faster than any other route for the drug.

[CC]

@Qadgop the Mercotan

Smelling it is actually the most direct route to the brain that there is.

The first cranial nerve, the olfactory nerve, is really just a modified portion of brain tissue extending over the cribriform plate in the ethmoid bone. The olfactory nerve feeds into the limbic system and the cerebrum itself, rather than the brainstem.

Olfactory nerve - Wikipedia
http://mywebpages.comcast.net/epollak/PSY255_pix/Olfactory_bulb_netter.JPG

So if receptors for the substance exist in the olfactory nerve, they’ll be directly stimulated and respond faster than any other route for the drug.

Wow. That’s so cool. Much as I hate it, I love it when I discover my assumptions are wrong. There’s clearly a reason that the U of I and I parted ways while I was still a pre-med.