快猫短视频

EXPERIENCES during the first few weeks of a squid鈥檚 life etch themselves
permanently in its brain and help them hunt as adults, biologists in California
have found. If scientists can track down the molecules that bring about these
early changes, they may discover how the brains of animals and people are shaped
as well.

Early experiences affect adult behaviours and abilities. But in humans and
other vertebrates, teasing out the brain chemistry that causes this is hard,
because the wiring of our brains is so complicated.

So William Gilly and Thomas Preuss at Hopkins Marine Station in Pacific
Grove, California, decided to study squid. 鈥淪quid have a fairly simple nervous
system, but they show almost vertebrate-like behaviour,鈥� says Preuss.

When the squid Loligo opalescens is startled by a touch or a mild
electric shock, it jets away from the stimulus by squirting water from the base
of its body. Nerve impulses that direct many of the squid鈥檚 actions travel along
thick nerve fibres called giant axons. But the patterns of nerve cell activity
that lead to jetting are different in juveniles and adults. Young squid fire the
giant axons first, but adults briefly suppress this signal so that they can
precede it with a rapid series of signals from other nerve cells called
non-giant axons. This produces a delayed but more powerful jet.

Preuss and Gilly suspected that this altered adult behaviour developed early
in life as a way of helping squid hunt fast-moving prey. So they raised one
group of hatchlings on sluggish baby brine shrimp, and another on speedy
copepods. Because copepods are too fast to be captured by pouncing, the squid
must learn to position themselves in front of the prey and wait for it to jump
into their tentacles.

Every day the researchers wired some squid with tiny electrodes and measured
the activity in their axons in response to a shock. Early on, all the squid
fired their giant axons first most of the time. When they were four weeks old,
the squid fed on slow shrimp retained nearly the same firing pattern. But those
chasing copepods had shifted almost entirely to the delayed, concerted pattern
of nerve-cell firing.

If the giant axon reflex fired as the copepods darted about it might spoil
the hunt. 鈥淭hey have to learn to suppress the strong reflex for successful
capture of the copepods,鈥� Preuss says.

The next step for researchers will be to look for proteins and
neurotransmitters that change the squid鈥檚 nervous system in this way, says
Hillel Chiel, who researches the neurological basis of behaviour at Case Western
Reserve University in Cleveland, Ohio. 鈥淭hat鈥檚 very exciting,鈥� he says. 鈥淭he
cast of molecular characters often turns out to be the same in vertebrates.鈥�