Begeleide axonen; op weg naar meer inzicht in de werking van hersencellen
Wat hebben Kurt Cobain, Ronald Reagan, Vincent Van Gogh en Muhammad Ali gemeen? Naast hun bekendheid lijden ze ook aan een hersenaandoening, respectievelijk een bipolaire stoornis, alzheimer, depressie en parkinson. Ook in uw omgeving kent u wellicht mensen met dergelijke aandoeningen.
Het grote probleem
Het veelvuldig voorkomen van deze aandoeningen en de hoge kosten die hiermee gepaard gaan, 680 miljard euro in Europa alleen al, stimuleren het onderzoek naar de werking van de hersenen. Dankzij de ontwikkeling van nieuwe technologische technieken kunnen we ons inzicht en onze kennis vergroten.
Onze hersenen zijn opgebouwd uit een gigantisch aantal cellen. Ruw geschat heeft ieder van ons zo’n 86 miljard hersencellen of neuronen. Deze neuronen zijn opgebouwd uit 3 delen: een cellichaam, een netwerk van vertakte uitlopers ook wel dendrieten genoemd en tenslotte een lange uitloper die zorgt voor het doorgeven van prikkels, het axon. Hersencellen zenden continu elektrische signalen of pulsen naar elkaar. De plek waar een signaal van het ene neuron naar het andere springt, wordt de synaps genoemd
De oplossing
Om meer inzicht te krijgen in neurologische aandoeningen moeten we deze elektrische signalen beter kunnen meten. Verschillende technieken zijn hiervoor in ontwikkeling. Zo kan men deze pulsen “in vivo” meten; d.w.z. rechtstreeks in de hersenen met behulp van elektrodes. Deze methode is niet eenvoudig en vrij gevaarlijk. Het kan mogelijk hersenschade veroorzaken. Een alternatieve methode om meer te weten te komen over de processen die zich afspelen in de hersenen is het “in vitro” laten groeien van hersencellen. Hierbij worden cellen uit de hersenen verwijderd en in een laboratorium gekweekt op bvb. een chip met elektroden. Deze elektroden zijn beschikbaar in verschillende vormen, materialen en groottes en kunnen elektrische signalen opvangen.
In het Haesler lab van NERF (Neuro-Electronics Research Flanders) wordt zo een nieuwe innovatieve ‘in vitro‘ elektrodetechnologie ontwikkeld waarbij neuronen synapsen vormen met elektrodes: de synaptrode interface. (zie afbeelding…)
De thesis
De elektrische signalen die we kunnen meten aan deze “synaptrodes” zijn ontzettend klein. Verstoringen of ruis moeten we dan ook zoveel mogelijk proberen te beperken. Zo zorgt de activiteit van cellichamen die in de nabijheid liggen van de neuronen voor ruis. Dit type ruis kunnen we vermijden door de synapsen te scheiden van de cellichamen. In mijn thesis werden 2 technieken onderzocht om deze scheiding te bewerkstelligen: kleine kanaaltjes gemaakt van een flexibel kunststofmateriaal en groeven direct uitgegraven in een chip. De axonen van de hersencellen kunnen zowel doorheen deze kanaaltjes als in de groeven uitgroeien. Zo komt een scheiding van cellichamen en synapsen tot stand en kan ruis in de elektrische signalen aan de synapsen voorkomen worden.
Voor de vervaardiging van de kanaaltjes gebruiken we een “molding” techniek. Deze techniek is vergelijkbaar met het maken van een gipsen afgietsel, maar dan op microschaal. We starten vanuit een “master” waar we een flexibel kunststofmateriaal op laten uitharden. Na uitharding van de kunststof en verwijdering van de master bekomen we kanaaltjes met slechts een dikte van 1/10e van een mensenhaar. Deze kanaaltjes brengen we daarna aan op een chip. Aan het ene uiteinde van de kanaaltjes plaatsen we de neuronen met hun cellichaam. De axonen van de neuronen kunnen dan door de kunststofkanaaltjes groeien om aan het andere uiteinde mogelijke synapsen te vormen.
Om groeven te maken, nemen we rechtstreeks materiaal weg van een chip. Ook deze groeven hebben een dikte van slechts 1/10e van een haar. De groeven begeleiden de axonen in hun groei.
Voor de uiteindelijke experimenten gebruikten we tijdens onze thesis hersencellen van muizen. Deze cellen werden aan het ene uiteinde van de structuur geplaatst en hadden dan 10 dagen de tijd om doorheen de kanaaltjes naar het andere uiteinde te groeien (Zie afbeelding). Na diverse tegenslagen zoals het afsterven van de hersencellen, uitdrogen van de kanaaltjes, contaminatie door bacteriën en schimmels, enz. lukte het om de neuronen doorheen de kanaaltjes te laten groeien. Voor het vervolg van het onderzoek, het vormen van synapsen na groei door de kanaaltjes, zijn bijkomende experimenten nodig.
Als gevolg van de Covid-19-omstandigheden kon geen onderzoek opgestart worden naar de werking van de groeven.
De toekomst
De weg naar behandeling van neurologische aandoeningen is nog lang. Wetenschappelijk onderzoek en nieuwe technologische technieken moeten zorgen voor voortschrijdend inzicht. Het onderwerp van deze thesis, nl. het ontwikkelen van technieken om de kwaliteit van het meten van de elektrische activiteit aan de synapsen van de hersencellen te verhogen, vormt een bescheiden stap in een “never ending (re)search story”.
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