Maturation of regenerating nerve assessed by evoked potential in the rat: hyperbolic time course.

Recovery of sensory fiber excitability after sciatic nerve lesion induced by freezing was assessed by the somesthesic evoked potential (SEP) in response to plantar pad electrical stimulation. SEP was recorded from the S1 area through chronically implanted cortical electrodes. The P1 wave reappeared on Day 22 or 23 postinjury, indicating that the axonal elongation rate ranged between 3.9 and 4.1 mm/day. P1 onset (P1o) latency decreased from 61.9 +/- 6.4 ms (SD) on Postoperative Day 22 to 18.8 +/- 1.13 ms on Day 50. Computation of standardized residuals showed that the best values for the regression equation as a function of time were obtained after hyperbolic transformation. Covariance analysis showed significant differences between untreated animals and after treatment with thyroxin (T4) and metformin p-chlorophenoxyacetate (MP) or after conditioning lesion (CL). This indicates that these treatments acted selectively on the components of the maturation process.

Inhibition of the preovulatory LH surge after a catecholestrogen (2-hydroxyestrone) antiserum injection in the third ventricle of cycling female rats.

Administration of a catecholestrogen (2-hydroxyestrone, 2-OHE1) antiserum (2-OHE1-AS) in the third ventricle of cycling female rats, on the morning of proestrus, leads to a significant reduction in the afternoon LH surge. These responses are dose-dependent and can be observed even when the 2-OHE1-AS is injected on the diestrus morning. Almost similar results were obtained with an antiserum against 17 beta-estradiol (17 beta-E2). Nevertheless, the fact that the central immunoneutralization of 2-OHE1 impedes the preovulatory surge of LH at a time of high peripheral levels of 17 beta-E2 strengthens the idea of a specific role for 2-OHE1 in the control of cycling LH release.

Dissociation between respiratory phase switching and phasic phrenic response on low-intensity stimulation of pneumotaxic complex and nearby structures.

Excitatory and inhibitory phasic phrenic responses (ePPR and iPPR) and inspiratory on-switch and off-switch (I-ON-S and I-OFF-S) were compared on stimulation of the pneumotaxic complex and neighboring reticular formation in cats anesthetized with nitrous oxide, curarized and spinalized at the C7 level. Stimulation consisted of a single pulse or train of 2 to 5 shocks whose intensity ranged between 100 and 300 microA. Single shock stimulation of the Kölliker-Fuse (KF) nucleus and of a region 1 mm just caudal evoked a pure iPPR during the phrenic burst. With single pulse of high intensity delivered in the second half of inspiration (I), the iPPR was associated with I-OFF-S. Single shock stimulation of a wider brain stem area including the medial part of the nucleus parabrachialis medialis (NPBM), nucleus parabrachialis lateralis and adjacent lateral and central tegmental fields evoked early iPPR combined with a later ePPR when delivered in I, and ePPR alone during expiration (E). Train stimulation of much more restricted areas could evoke I-ON-S or I-OFF-S depending on the site of stimulation and time of delivery in I or E. Definite dissociations occurred between iPPR and I-OFF-S according to the place of stimulation. A maximal iPPR, obtained from a region ventral to the NPBM, was never found to be associated with I-OFF-S. The excitability of I-ON-S, and ePPR amplitude showed opposite time-courses during E and had different latencies.(ABSTRACT TRUNCATED AT 250 WORDS)