Hi Sak,

Ketamine/xilazine or ketamine/medetomidine are good for in vivo preparations, as well as urethane. But take in account Ketamine is a NMDA blocker, so you may find weaker NMDA-mediated responses in that kind of prepararion if you are studying these receptors specially.

A lot of people is moving to the continuous isuflorane anesthesia, which allows to control very smoothly the level of anesthesia, which is an advantage for studying brain states, for example.

These are the most commonly used in EEG and ECG recordings in rodents.

I second the vote for isoflurane.  Induce rodents with 4% for 3-5 min then maintain at 1-1.5%.  Injectables are notoriously difficult to manage in rodents, especially for procedures that take more than 20 min.

We get decent responses in the hippocampus under isoflorane as well.

Thanks for your suggestion and what about urethane anesthesia? 

Urethane works very well for many hours but has 3 disadvantages.  It is highly carcinogenic to humans, the animal does not survive its use, and the anesthetic dose is not very far from the lethal dose. We divide into 4 or more aliquots given 15-25 min apart.  The gradual induction seems essential to survival.

Urethane switches spontaneously from 'deep' states to 'activated' REM-like states and vice versa, while the other anesthetics are more stable if you give the adequate dose.

Thanks to all... so, Isoflurane is the best one for electrophysiological recordings... 

Isoflurane may be a good choice if you have the necessary equipments. If you prefer to use injectable anesthetics, another possible anesthetic would be chloral hydrate. We used it in electrophysiological experiments, however not during EEG recording but single unit recording (see attached publication). It can be administered continuously intravenously.

In other studies we used ketamine+diazepam, this type of anesthesia is also suitable for single-unit recordings. However, the anesthesia can considerably affect electrophysiological recordings, e.g., we recognized that hippocampal pyramidal cells are quite active under chloral hydrate anesthesia, but they were silent under ketamine (ketamine is an NMDA antagonist).

Unfortunately, chloral hydrate - similarly to urethane - can only be used in non-survival experiments (because it may be harmful for abdominal organs when administered IP). Animals survive ketamine anesthesia, however it may cause symptoms like schizophrenia and may affect mismatch negativity.

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Yes, you can use chloral hydrate for rapid surgeries. It presents fast pharmacokinetics and the awakening is pretty easy. I was not aware of its damage to abdominal organs, but you may use a SC infusion pump for a long-term anesthesia.

In the lab of JM Delgado and A Gruart they are using it for quick surgeries for chronic LFP experiments, as far as I know.