Feeding Elicited by Microinjections, Lab Report Example

Question 1: For 10 points, neatly graph the food intake and latency data so as to most clearly represent the findings.  This could be bar graphs, line graphs or even a table.  Include a measure of both the central tendency (i.e., the mean or median) and the variability (individual data, standard error of the mean, or standard deviation).  Write a brief description of the results.

Table 1:

Summary of experiment results

Table 1 above shows comparison between findings from the vehicle experiment and the DNQX.  The mean latency period for the control was 43.18 while that of the independent experiment was 30.  Average food intake in the control was 0 but on the independent case was -0.027g.

Chat1:

Line graph of latency period vs. food intake in that period for the two experiments

From the graph there is no variation in latency in the vehicle case experiment while the case control has a latency variation of between 25 and 45 minutes

Question 2: Ideally there is only one difference in the treatment of the control and experimental subjects.  This treatment is called the independent variable.  The independent variable in this week’s lab was the application of DNQX to the nucleus accumbens.  However, because of the experimental design there were several differences in the control treatment and the experimental treatment.  What was at least one of these differences and how would you redesign the experiment to eliminate this (these) problem?

Deference noticed include: latency period, this should be standardised. Other differences occurred in rat behaviour during study. The different behaviours like locomotion should be studies and made independent to further show different effect of certain controls.

Question 3: DNQX not only antagonizes AMPA receptors, but also antagonizes kainate receptors (another ionotropic glutamate receptor type). Design an experiment to determine which receptor type may mediate the behavioural effects we see in class. Discuss why you think your experiment idea can discriminate whether or not the effect is specific to the AMPA receptor.

In order to investigate effect of AMPA receptors we shall design an appropriate experiment to study the effects of AMPA receptors on feeding habits of rats.

To carry the above study we shall require two groups of satiated rats. We shall inject each with a solution of AMPA in 5% sucrose and introduce them to acrylic cages in different rooms having weighed and equal quantities of food pellets. The injections hall be done on the ACBsh.

AMPA suppresses eating habits; we thus expect that the rats injected with AMPA sucrose solutions to eat the food pellets even though they are full. The rats with no control should not eat or even if they eat it should be significantly less than those who were injected with AMPA.

Question 4: If injection of a local anesthetic into the nucleus accumbens stimulates eating, is it possible that DNQX stimulated eating not because it blocks receptors but rather because it has properties of a local anesthetic?  Design an experiment(s) focused on determining whether DNQX’s effects are related to its receptor blocking actions or to possible anesthetic effects. Note – Local anesthetics work by blocking action potentials and they do this by blocking voltage-gated Na⁺ channels.

To study the above it will be necessary to use brain micro-dialysis experiment through zone capillary electrolysis with laser induced fluorescence detection (CZE-LIFD) that will allow measuring of glutamate every 5s.

The study rats will be prepared; group 1 rats will be injected with local anaesthesia while group two will be injected with DNQX solution. They will then be put under wire cages with food and water. Micro-dialysis probes were constructed of fused glass tubing. Probes were perfused using ringer solution and readings from samples taken every 30s. The micro dialysis probes were inserted in either the LH or ABC.

Question 5: How do we know that the rats are specifically feeding, and not feeding only as a consequence of general behavioural arousal (i.e. looking for something to gnaw on)?

To answer the above question it would be necessary to carry out an experiment to determine the eating behaviours of satiated rats and deprived rats. It is known that blocking the non-N-methyl-D-aspartic acid (NMDA) ionotropic glutamane receptors in the AcBSh or accumbens shell using DNQX-dinotroquinonxaline-2, 3 dione, an antagonist of glutamate receptors of the AMPA subtype causes intense feeding in satiated rats. The nucleus accumbens (ACB) known for its role in reinforcing process is a key determinant in mediating feeding behaviour. Use or injection of opoid agonists into the nucleus accumbens can increase food intake in satiated rats or non-deprived rats while injections of opoid receptor antagonists into the nucleus accumbens can suppress feeding Application of these finding can assist to determine if the resultant feeding is part of general behaviour activation or is artificially elicited/controlled.

To carry out the above experiment two groups of rats would be necessary to study. Group one shall form the control group where the test shall be done while the second group shall be independent of any study interventions.

Rats used in the experiment shall have equal satiation levels prior to study so as to control for deprivation. Rats with similar satiable levels shall be introduced into a cage with food pellets. They shall be kept within the cage and the time take to eat to satisfaction recorded. They shall be moved to a new cage with food pellets and injected with opoid agonist. Their eating behaviour shall be studied within a given time period and the amount of food eaten recorded.

Second group of rats shall be introduced into the first food cage and time taken to eat to satisfaction recorded. They shall then be moved to a new cage with more food and the amount of food consumed within similar timings to the control group recorded, general eating behaviour shall also be checked. Eating behaviour of rats from the two groups shall be studied and significance recorded.

Question 6: Do your results prove that when a rat stops feeding (perhaps from eating to satiety) that glutamate is being released into the accumbens, acting on AMPA receptors? If not, propose an experiment to provide evidence for this claim, and then discuss your reasoning for this answer.

The results prove that when a rat stops feeding glutamane is being released into the accumbens acting on the AMPA receptors tasked with suppression of feeding.

The DNQX injected into the accumbens blocks the non-NMDA ionotropic glutamane receptors. This causes a very specific increase in food uptake. Glutamane acts on AMPA receptors thereby suppressing/controlling feeding behaviour. From the experiment there was no feeding noticed in the rats injected with DNQX in the accumbens.

The DNQX acted to increase AMPA activity within the accumbens thereby suppressing food intake.

Question 7: Nucleus accumbens injections of DNQX could induce feeding by causing a hormone, such as insulin, to be released into the bloodstream.  This hormone, could in turn, cause the level of blood glucose to fall and thereby induce the rat to eat in response to low blood glucose.  Design an experiment that would eliminate this possibility. 

In order to eliminate induced feeding through insulin we shall design an experiment that test for effects of low and high sucrose. We shall test two groups of rats under similar conditions but provided with different sucrose concentrations and compare to a third group having similar conditions but injected with AMPA 50ng  in sucrose solution

We shall inject group one rats with a solution of DNQX (750ng) and provide them with a pre weighed quantity of food. They shall be injected with sucrose solution of about 1%. The second group shall be injected with a solution of DNQX (750ng) and provide them with a pre weighed quantity of food. They shall be injected with sucrose solution of about 100%.The rats will be tested in acrylic cages in different rooms. The experiment will be carried out for about 30 minutes and behavioural tests done in each group to compare.

The first and second group experiments shall be repeated but the rats shall be in injected with AMPA 50ng presented with a 5% sucrose solution.

The experiment is expected to show varying levels of feeding in the first experiments group as  a result of varying sucrose levels there by proving that sucrose levels do determine feeding habits. The second phase or third repeat of the experiment should show similar eating habits irrespective of sucrose levels as this is the control. AMPA injected into the ABC serves as a control to varying levels in sucrose solutions within the body.

Question 8: In relation to the previous questions, describe an experiment that might not only eliminates this possibility but might also eliminate the possibility that DNQX-induces feeding consequent to the release of any peripheral hormone, including those that haven’t yet been discovered!  Hint:  The experiment I’m thinking of involves injecting DNQX into the nucleus accumbens on only one side of the brain and measuring a specific aspect of the rat reaction to food.  Hint 2:  A hormone in the blood would affect both sides of the brain.

To study the above it will important to determine effects of glutamane on eating habits. This is because glutamane being an excitatory neurotransmitter in the brain most neurons will respond to exogenously applied glutamate, reflecting their expression of glutamate receptors and synaptic or extra synaptic input from glutamatergic neurons.

To carry the above study glutamane was injected into the LH and the ACB of rats (satiable). They were then put in a cage with weighted food pellets. The amount of food they ingested was then measure by time.

The findings were similar to that of ant experiments that used DNQX or any other compound that works to affect eating habits.

Question 9: Lets assume for this question that nucleus accumbens injection of DNQX did elicit eating by its actions on neurons that normally regulated eating behavior.  Noting that other behaviors (drinking, sexual behavior, predatory attack, locomotion) can also be produced by central injection of neurotransmitters, receptor agonists or receptor antagonist, what is a general conclusion about brain function that might be suggested by the fact that in injection of a single neurotransmitter (or receptor antagonist) into a single brain area is capable of triggering a complex temporally patterned behavior like eating?

Brain function is complex and structured in a definite and seamless way. The experiment on rats has shown that injection of DQNX into the ACBSH or nucleus accumbens elicits or triggers feeding. Just as this temporary feeding acquired behaviour injection of AMPA or D-AP5 blocked the response or suppressed eating habits. Due to complexity and uniqueness of brain functions central injection of neurotransmitters are specific to regions and may not work when applied to other areas. For example the D-AP5 or AMPA will not elicit the same response when injected into the contralateral lateral hypothalamus (LH).

The brain functions are seamless and structured which leads to suggestions that anatomical interactions between the various brain areas that mediate certain or any required Reponses are ipsilateral or as a result of direct projections between the relevant brain areas for example suppression of glutematergic inputs in the ACB through injection of DPMA will elicit eating through removing on going inhibitions in the ACB and GABAegic projections to the LH.

Although the above discussions hold past research has shown for instance show that significant glutamate increase observed during feeding shows that glutamate in the LH plays a significant role in feeding. Nevertheless this cannot be causally linked to feeding to show that increase in glutamate is responsible for triggering feeding but there correlation as stated is high.

Question 10: DNQX appears to elicit feeding in the ACBsh. However, when injected in other regions, it could have very different effects. For example, when administered to the hippocampus it appears to inhibit memory formation, but it does not directly effect food intake. What does this say about the region that the drug is infused into? From this concept, would you suppose that one neurotransmitter would have one behavioral function?

Each region of the brain is tasked with carrying out a given function making it specific. This will dictate the type of response required to avoid any contradiction. Injection of DNQX within the ACBsh will elicit eating habits as this region is tasked with control of such like habits. Injection of the DNQX in the hippocampus region will result inhibition of memory formation.

Neurotransmitters act by binding to specific receptors in the brain (neuronal postsynaptic membrane). Through the binding it can inhibit or excite the neighbouring neuron so as to increase its activity. The brain is grouped into different areas with neurotransmitters and specific neurotransmitter receptors for each region. Brain regions include Noradrenaline, serotonin and the dopamine. Each has its emotions it responds to.

Neurotransmitters may have one behaviour function but it’s the transmitter they attach to that dictates the difference in behavior.