G. Fontanesi et al., CYSTEAMINE-INDUCED DEPLETION OF SOMATOSTATINERGIC SYSTEMS ALTERS POTENTIALS-EVOKED FROM THE RAT VISUAL-CORTEX, Visual neuroscience, 13(2), 1996, pp. 327-334
This study was performed in order to establish whether selective deple
tion of somatostatin (SS) in the rat primary visual cortex obtained by
cysteamine (CSH) administration results in changes of visual evoked p
otentials (VEPs). VEPs in response to a contrast reversal (0.5 Hz) of
an optimal sinusoidal grating (0.1 cycle/deg, contrast 90%, mean lumin
ance 15 cd/m(2)) were recorded from different layers of the binocular
portion of the primary visual cortex of anesthetized rats with saline
injection as well as before and after CSH treatment (90 mg/kg, s.c.).
VEPs of CSH treated rats, as compared to those obtained either in sali
ne-injected animals or before drug administration, are reduced in ampl
itude at intermediate cortical layers whereas they are increased at de
eper layers. VEP changes depend on CSH treatment and not on the extend
ed anesthesia since no alterations in the VEP profile can be observed
in saline-injected animals maintained in the same experimental conditi
on. Forty-eight hours following CSH treatment, the VEP profile is comp
arable to that of saline-injected animals. Immunocytochemical analysis
of the visual cortex of rats recorded 7 h after CSH treatment shows a
20-30% reduction in the number of SS-containing cortical cells. The h
ighest reduction can be observed in cortical layer 5 although a signif
icant decrease is also found in layers 2-3. In contrast, the pattern o
f SS immunoreactivity of the visual cortex of rats recorded 48 h after
CSH administration is similar to that obtained in control conditions.
These results indicate that a selective toxin for somatostatinergic s
ystems induces a transient decrease of SS-containing cell number in se
lected cortical layers. Accordingly, CSH can serve as a useful pharmac
ological tool for the study of somatostatinergic function in the rat v
isual cortex since changes in VEPs can be related to a reduction of so
matostatinergic neurons associated to CSH treatment. In particular, th
e present results suggest that one of the possible actions of somatost
atinergic neurons in the rat visual cortex is to modulate the excitato
ry-inhibitory balance.