Neurotransmitters, Neuroregulators and Neurotoxins in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 144

of monoamine, amino acid and acetylcholine in synapses (Chatterjee et al.
1998; Buchholzer et al. 2002). Evidence that hyperforin modulates mam-
malian neurotransmitter metabolism has also been found in in vivo studies
(Buchholzer et al. 2002). Interestingly, hyperforin is not unique to St. John's
wort but was recently also found in a completely different medicinal plant
species, Scutellaria baicalensis Georgi. (Murch et al. 2004b). Therefore,
a role for hyperforin in plant metabolism seems likely.
The ability to detect, quantify and optimize production of neuroregula-
tory molecules from plants is crucial to the discovery of new molecules and
mechanisms for treatment of human diseases. Plant-derived cannabinoids
have a variety of medicinal properties, including analgesia, antiemesis,
antiglaucoma via reduction of intraocular pressure, and reduction of in-
jury (Biegon 2004). Plant symptoms of multiple sclerosis and mediation
of the repercussions of traumatic brain-based neuroprotective compounds
are especially useful since the surgical repair of neurological damage is
frequently impossible. Neuroprotective agents from plants include antiox-
idants, NO synthase inhibitors, AMPA antagonists, Ca 2+ channel blockers,
estrogen agonists and others (Levi and Brimble 2004).
In a recent study, we discovered 781 medicinal compounds in S. baicalen-
sis , including 27 antibiotics, and new amino derivatives of baicalin and
baicalein that were not previously known (Murch et al. 2004b). The concen-
tration and chemical profile of medicinal species was found to be dependent
on both the germplasm (Murch et al. 2004b) and the growth environment
(Murch et al. 2003; Zobayed et al. 2003). Indeed, St. John's wort plantlets
exposed to a metal ion stress completely lost the capacity to produce hyper-
forin or hypericin (Murch et al. 2003); therefore, the neurological activity
of a whole plant preparation could vary with the preparation of plant
tissues from different regions and different seed collections. As well, the
often-identified marker compounds thought to be characteristic of a single
species may not be unique and may not be related to the physiological
response of a human. Much further study of the metabolome of medicinal
plantshasenormouspotentialforthediscoveryofnew,neurologicallyac-
tive drugs for treatment and prevention of human diseases, but may also
lead to new understandings of the control of plant growth and development.
10.3
Neurotoxins in Plants
There is another group of neuroregulating compounds that includes neuro-
toxinsandallergensandtheinvestigationofthesecompoundscanprovide
new insights into some of the most chronic and devastating human diseases.
Many of these toxic plant compounds are unusual non-protein amino acids