Guseva and Pauly 2006 - Regulation of rat brain nAChR binding in vivo by dietary choline

What is the primary objective of this study?

To evaluate region-specific changes in rat brain nicotinic acetylcholine receptor (nAChR) subtypes following dietary choline modification.

What are the secondary objectives of the choline study?

To assess choline’s action on α7 versus non-α7 nAChRs, monitor physiological outcomes, and investigate effects on cognitive functions using the Morris Water Maze test.

What is the main hypothesis regarding choline's action on α7 nAChRs?

Choline acts as a selective agonist at α7 nAChRs, upregulating them without significantly affecting non-α7 receptor subtypes.

What physiological outcomes were monitored in the choline study?

Body weight changes, food and water intake.

What methods were used to assess cognitive function in the study?

The Morris Water Maze (MWM) test was used to evaluate spatial learning and memory.

Describe the α7 nAChR.

α7 nAChR is a homomeric nicotinic receptor that has a wide distribution in the mammalian CNS and high Ca permeability.

How does choline supplementation affect body weight and consumption in rats?

Choline supplemented animals drank less water in the latter days of the experiment. They also weighed less.

What was concluded about the effects of dietary choline on cognitive evaluation?

Dietary choline supplementation does not improve spatial learning in the Morris Water Maze test.

How long did the choline treatment last for the rats in the study?

Choline treatment lasted either 14 or 28 days.

What are the 3 choline transporters that have been identified?

1. Low-affinity choline transporter (LACT)

2. High-affinity choline uptake site (HACU) transporter

3. blood–brain barrier (BBB) transporter

What action does Choline have on nAChRs?

Choline is likely a direct agonist for nAChRs.

What subjects did the study use?

The study used 31 day old male Sprague-Dawley rats.

How long did diet manipulation last?

Dietary manipulation lasted 14 or 28 days.

How was daily food consumption calculated?

daily food consumption = Yesterday’s food oz - today’s leftovers oz

How was daily water consumption calculated?

Spillage control water bottles were weighed daily

How often were rats weighed?

Rats weighed every other day

Rats were divided into 3 dietary groups:

1. Choline-deficient - 0% choline

2. Standard-Choline - 0.2% choline

3. Choline-Supplemented - 2% choline

Describe the Morris Water Maze procedure.

• Procedure: 20 acquisition trials were administered: 4 per day for 5 consecutive days, starting after 2 or 4 weeks of diet

  1. Quadrant entry was randomized and they were allowed to swim until they found the platform, where they remained for 15 sec

     • Rats unable to locate the platform in 60 sec were placed on the platform and allowed to rest for 15 sec

  2. Four hrs later, the platform was removed and a 30 sec probe trial occurred

What ligand was used for non-a7 binding? What was the exposure time?

Epibatidine was used for non-α7 binding with a 3 day exposure time.

What ligand was used for non-a7 binding? What was the exposure time?

α-Bungarotoxin (BTX) was used for α7 binding with a 3 day exposure time.

What were the results of the autoradiographies (3 things)?

• No increases in non-α7 nAChRs for any group or length of diet.

• 2-week Choline supplementation increased the density of α7 nAChRs in the cerebral cortex, endopiriform nucleus, hippocampus and superior colliculus. No differences in α7 nAChR binding in the standard or choline deficient diets

• 4-week Choline supplementation provided no increases in nAChRs for any group.

How might nAChR subunit mRNAs and α7 and β2 receptor proteins lead to decreased weight in choline-supplemented rats?

These are present in rat adipocytes. Chronic stimulation of rat adipocytes with nicotine has been shown to induce release of adiponectin, a compound that may lower body weight in humans.

How was the finding that Dietary choline supplementation doesn’t improve spatial learning expanded upon?

Up-regulation of α7 nAChRs alone does not appear to be sufficient for cognitive enhancement, despite chronic nicotine administration studies showing enhanced cognitive performance coinciding with increased nAChRs.

What are some nAChR upregulation characteristics (5 total)?

1. dose-dependant (a7)

2. rapid (within 24hr; a7)

3. Lasts for 7 days (a7)

4. receptor density declines to control levels after supplementation ends (a7)

5. present after 31 days of dietary choline (non-a7)

Why does this study not match up with others like it (3 reasons)?

1. Receptor binding methods used were different.

2. Pharmacokinetic issues such as bioavailability of choline chloride (drinking solution) administered in solid form (food) versus the solution (water)

3. Polydipsia caused increased removal of choline

Why was there no α7 nAChR decrease in this study’s choline deficient group?

The lack of α7 nAChR decrease in the deficit group may be due to replenishment of choline in the brain via phosphatidylcholine, which resynthesizes ACh.

What is the precursor to ACh and phosphatidylcholine?

Choline

What are 3 reasons they provide for the lack of α7 nAChR up-regulation after 28 days of choline supplementation.

1. changes in the magnitude and/or duration of receptor desensitization

2. Developmental change in the number and/or efficacy of BBB choline transporters

3. Choline catabolism could also change with chronic supplementation or development