Kevin's Watch

The change to their behaviour was permanent.

duchess of malfi wrote:I find it very disturbing.

If having a person with poor parenting skills as a mother marks you for life, than I am forever doomed.

Murrin wrote:Yes, it's worth pursuing for its benefits - but the other possible applications are worrying. The fact that the first evidence they've had was through behaviour modification could be taken as a possible sign of things to come.

DELIVERING SUBSTANCES INTO THE CNS

METHODS OF INJECTION

There are a variety of ways in which one can deliver agents into the CNS. This can be done peripherally (such as by giving a drug orally or intravenously), or else locally, using stereotaxic methods. When it comes to using stereotaxic methods for local delivery of a substance, one needs to consider the following main questions:

1) what do you want to deliver?;

2) where do you want to deliver the substance?;

3) how much of the substance do you want to deliver, and

4) for how long does this agent need to be administered?

By considering all these questions, one can then design the most effective, and cost-effective, means for delivering agents into the mammalian CNS. Following these questions, you will find detailed descriptions for using the following injection devices: Hamilton syringes The “Nanojector” system with glass micropipettes Alzet micro-osmotic pumps.

Note: Always keep in mind that the CNS is, anatomically, a “closed system” in that it is susceptible to increased pressure, and is thus only able to handle small injection or infusion volumes. Further, the CNS itself is very delicate, and can be damaged very easily. These cautions must always be taken into account when designing any experiment using stereotaxic methods.

What do you want to deliver? Another section of this course deals with the subtleties of the use of various agents for injection, so for the purposes of this discussion, agents to be delivered directly into the CNS can be anything such as drugs, bioactive antibodies or peptides, cell cycle markers (such as BrdU), toxins, trophic factors, cells, polymers, axonal tracers, or viral vectors.

Of course, what you can deliver into the CNS will depend upon the biophysical and biological properties of the substance to be injected. Is it water-soluble? Will it handle the pH conditions of the brain?How well will it disperse within the CNS (and do you want it to disperse)?Where do you want to deliver the agent?You can, in principle, deliver almost any agent to the CNS, and the ability to do so is often simply limited by the ability to get access to that region. Where you deliver a substance will have a great influence over how well that substance can be taken up into the tissues, and how far it will disperse.

For example, a substance will flow more easily throughout the CNS if it is delivered into the ventricular system than if it were injected into the parenchyma (brain cell tissue) itself. The lateral ventricles are a very common site for injection, because of their size and their ability to accept larger volumes of liquid than the CNS parenchyma.

However, almost every brain region has, at one time or another, been the target site for injection of some sort ofsubstance. The only limiting factors for where to inject an agent is, really, access to that site. It is of course much easier to infuse a substance into the CNS ventricles than it is to put it into the brain stem, spinal cord, or retina. However, with practice and surgical modification, this too can be done.

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