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TEL.14 – Manipulation of serotonin transmission on behavioural and neurochemical deficits…
dendrite category, dendrite diameter and spine density were estimated as a
function of the branch order under higher magnification. All protrusions with
or without bulbous expansions were counted as spines if they were in direct
continuity with the dendritic shaft. Densities of spines on the apical and basal
dendritic trees were averaged for a neuron mean, and the six neurons from
each mouse were averaged. Spine density was then estimated as a function of
the branch order on apical and basal dendrites. We observed in phenylketonuric
mice reduced spine density in both apical and basal dendrites. Moreover,
analysis of spine maturation revealed that ENU2 mice exhibited more
spines with immature shapes that did controls on apical dendritic shafts.
These observations, in agreement with human data of pathologic alterations
of axons, dendrites and synapses in PKU brain [Bauman et al. 1982;
Huttenlocher 2000; Kornguth al. 1992], might represent mechanism by which
reduced brain amine availability during postnatal development produces cognitive
impairment in PKU subjects.
2. 5-HTP treatment during critical period prevents morphological alterations
in medial pFC neurons of ENU2 mice
On the basis of our previous work [Pascucci et al. 2008], we treated ENU2
developing mice (P14-P21) with 5-HTP (20 mg/kg, twice to day). Brains of 5-
HTP- and saline-treated adult ENU2 mice were utilized for the Golgi analysis
and prepared as previously reported. Analysis of morphological characteristics
of medial pFC neurons revealed increase of spine density in basal dendrites
of 5-HTP-treated in comparison with saline-treated ENU2 mice. Moreover,
analysis of spine maturation revealed that 5-HTP treatment caused an
increase in the number of spines with mature shapes.
3. Hyperphenylalaninemia disables cortical serotonin transmission
by inhibition of tryptophan hydroxylase activity
Preliminary study investigated interference PHE-induced on aminergic
neurotransmission in the frontal lobes by evaluating, in vivo, amine release in
the pFC of adult ENU2 mice. Mice of the healthy background responded to a
psychogenic stressor with the classic time-dependent increase of NE, DA and
5-HT release from pFC terminals. Neither the dopaminergic nor the serotoninergic
responses were observable in ENU2 mice. Temporary reduction of
circulating PHE, by dietary restriction, promoted recovery of the serotonin
response only, demonstrating direct interference with 5-HT synthesis in the
mature brain. Evaluation of different steps of 5-HT synthesis in the pFC of
ENU2 mice demonstrated inhibition of cortical tryptophan hydroxylase
(TPH) activity. Finally, systemic administration of 5-HTP, the product of TPH
activity, completely recovered fronto-cortical 5-HT neurotransmission in
ENU2 mice. Instead, tryptophan administration was unable to increase cortical
5HT release of ENU2 mice (submitted data).
These results demonstrate that HPA interferes with the ability of the
mature pFC to respond to psychological challenges, point to the 5-HT synthesis
as the target of PHE interference, and support the use of 5-HTP in life-long
treatment of hyperphenylalaninemic subjects.
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