The dorsal hippocampus is crucial for learning the hidden-platform location in the hippocampus-dependent, spatial watermaze task. We have previously demonstrated that the postburst afterhyperpolarization (AHP) of hippocampal pyramidal neurons is reduced after acquisition of the hippocampus-dependent, temporal trace eyeblink conditioning task. We report here that the AHP and one or more of its associated currents (IAHP and/or sIAHP) are reduced in dorsal hippocampal CA1 pyramidal neurons from rats that learned the watermaze task as compared with neurons from control rats. This reduction was a learning-induced phenomenon as the AHP of CA1 neurons from rats that failed to learn the hidden-platform location was similar to that of neurons from control rats. We propose that reduction of the AHP in pyramidal neurons in regions crucial for learning is a cellular mechanism of learning that is conserved across species and tasks.

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Children prenatally exposed to alcohol typically exhibit behavioral abnormalities, including hyperactivity, learning deficits, and an increased prevalence of depression. Similar impairments are found in children of hypothyroid mothers, and we have shown that alcohol-consuming rat dams have suppressed hypothalamic-pituitary-thyroid (HPT) function. Therefore, we hypothesized that suppressed maternal thyroid hormonal milieu may contribute to the deleterious consequences of prenatal alcohol exposure. We aimed first to confirm and then to reverse the behavioral deficits in the fetal alcohol exposed (FAE) rat offspring by administration of thyroxine (T4) to the alcohol-consuming dams. Adult offspring prenatally exposed to ethanol (FAE; 35% ethanol-derived calories), pair-fed (PF) or control (C) diets were tested in the Morris water maze (MWM), the forced swim test (FST), and the open field test (OFT) to assess spatial learning, depressive behavior, and exploratory behavior/anxiety, respectively. Adult FAE offspring took longer to locate a hidden platform in the MWM and showed increased depressive behavior in the FST both of which were reversed by administration of T4 to the alcohol-consuming mother. We found sex and brain regionspecific alterations in expression of genes involved in these behaviors in FAE adult offspring. Specifically, decreased hippocampal GAP-43 mRNA levels in adult FAE females and decreased glucocorticoid receptor (GR) expression in the amygdala of male and female FAE offspring were observed. The decreased mRNA levels of GAP-43 and GR were normalized by T4 treatment to the alcohol-consuming mother. Our results suggest that the suppressed HPT function of the alcohol-consuming mother contributes to the behavioral and cognitive dysfunctions observed in the offspring. Prenatal alcohol exposure has long-term developmental consequences, 1-3 and in humans alcohol is recognized as a teratogen leading to long-lasting CNS dysfunctions. 4 Specifically, patients with fetal alcohol exposure (FAE) have marked cognitive deficits, including difficulty focusing and sustaining attention, 5 and place learning deficits in a virtual Morris water task. 6 Attention deficit hyperactivity disorder (ADHD) is frequently diagnosed in FAE children. These neurocognitive and behavioral characteristics differ between FAE children and those with a primary diagnosis of ADHD, as FAE children have difficulties primarily in the encoding and retrieval of information. 7 A significantly increased prevalence of depression is also found in children 8 and adults 9 prenatally exposed to alcohol. It is important to note that, in contrast to the higher female prevalence of depressive disorders in the general population, the rate of depression found in adults with prenatal alcohol exposure was nearly equal among men and women. 9 Fetal alcohol effects qualitatively similar to those described in children with a history of gestational alcohol exposure have been detected with animal models. 10 Cognitive deficits have been found in FAE animal models...

Previous work in this laboratory demonstrated that the 19- and 35-day-old offspring of ethanol-fed rats have a significant deficiency of cortical serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), as well as a decrease in the number of total 5-HT1 receptors in the motor and somatosensory cortex. The present studies extend our previous reports by demonstrating that there is also a deficit of 5-HT and 5-HIAA in the motor cortex but not in the somatosensory cortex. In addition, we have shown that a deficit of 5-HT1A receptors in the motor and somatosensory cortices contributes to the deficit of total 5-HT1 receptors. In contrast, we did not observe any changes in the binding to 5-HT1B receptors in these cortical regions from the 19-day-old offspring of ethanol-fed rats. The present studies also examined the effects of in utero ethanol exposure on the early development of the serotonergic system. The results of these studies demonstrated a deficit of 5-HT and/or 5-HIAA in the brain stem as early as the 15th day of gestation (G15) and in the cortex as early as G19. In addition, we demonstrated a delay in both the normal developmental decline of 5-HT1A receptors in the brain stem and in the acquisition of cortical 5-HT1A receptors. No changes were found in the binding of [125I]cyanopindolol to 5-HT1B receptors in either region of fetal or neonatal rats exposed to ethanol in utero.(ABSTRACT TRUNCATED AT 250 WORDS)

The a-ketoglutarate-dependent dioxygenase aspartyl (asparaginyl) J-hydroxylase (EC 1.14. (18,19). A cDNA fragment (nt 1-1033) was deleted from bovine Asp (Asn) /3hydroxylase cDNA by digestion with Pst I and ligated to form pNC3d-1. A 1.4-kb cDNA insert [nt 1034-2498, containing a 233-bp 3' untranslated region (19)] resulting from Xba I/Xho I digestion was isolated and then cloned into an E. coli expression vector, pFLAG-1 (IBI) (20), to form p52-1.Since this 1.4-kb cDNA insert lacked nt 931-1033, a synthetic double-stranded DNA fragment containing these nucleotides, a HindIII site at the 5' end, and a Pst I site at the 3' end was inserted into p52-1 to form the expression plasmid p52. The cDNA reading frame (nt 931-2265) ofp52 was confirmed as follows: p52 was then used to transform E. coli DHSaF'IQ (BRL); it was then purified and the 5' ends ofthe cDNA insert were sequenced. Purified p52 was introduced into both a normal E. coli strain and a protease-deficient strain (BL21; Novagen).Expression of P52. A p52 transformant was grown at 37TC in 3 x LB medium (30 g oftryptone, 15 g of yeast extract, and 5 g of NaCl per liter, pH 7.5) to an OD595 of 0.4-0.6. The culture was diluted 1:40 with 3x LB and incubated at 3rC until an OD595 of 1.5-1.8 was attained. Expression was induced with 1 mM isopropyl P-D-thiogalactopyranoside for 4 hr at 28C.For the purification of P52 (Table 1), 300 g of frozen cellswere resuspended in 1.2 liters of ice-cold lysis buffer (50 mM Tris-HCI, pH 7.5/0.1% Nonidet P-40/3 mM EDTA with protease inhibitors) and lysed. Protease inhibitor concentrations were as follows: aprotinin, 3.0 Ig/ml; leupeptin, 1.5 gg/ml; pepstatin, 2.1 pg/ml; phenylmethylsulfonyl fluoride, 0.6 mM; soybean trypsin inhibitor, 0.01%; benzamidine, 10Abbreviations: EGF, epidermal growth factor; P52, 52-kDa recombinant Asp (Asn) P-hydroxylase.

Previous studies from this and other laboratories suggest that dopamine is decreased in selected brain regions of postnatal rats exposed to ethanol in utero. The present study expands previous work by examining the effects of in utero ethanol exposure on dopamine D1 and D2 binding sites and dopamine uptake in postnatal rats. In addition, dopamine content in the brain stem and frontal cortex of fetal and neonatal rats was examined. The experimental results indicate that in utero ethanol exposure markedly affects the postnatal development of the dopaminergic system in the striatum and frontal cortex. We observed a marked, transient deficiency of striatal dopamine (greater than 40% decrease at 19 days) and dopamine uptake sites (approximately 25% decrease in Vmax at 35 days). The Bmax for striatal dopamine D1 binding sites was decreased by greater than 20% at both 19 and 35 days. Cortical D1 sites were markedly decreased at 19 days (greater than 40%). In contrast, the number of striatal D2 receptors was unaffected by in utero ethanol exposure at both ages. Analysis of tissue from neonatal rats demonstrated a marked dopamine deficiency in ethanol-exposed rats on postnatal day 5. In light of the proposed morphogenic actions of dopamine early in development, it is possible that the early dopamine deficiency contributes to the abnormal postnatal development of the dopaminergic system.

A common cellular alteration, reduced post-burst afterhyperpolarization (AHP) in CA1 neurons, is associated with acquisition of the hippocampus-dependent tasks trace eyeblink conditioning and the Morris water maze. As a similar increase in excitability is correlated with these two learning paradigms, we sought to determine the interactive behavioral effects of training animals on both tasks by using either a consecutive or simultaneous training design. In the consecutive design, animals were trained first on either the trace eyeblink conditioning task for six sessions, followed by training on the water maze task for six sessions, or vice versa. The simultaneous design consisted of six or 11 training days; animals received one session/day of both trace eyeblink conditioning and water maze training. Separate groups were used for consecutive and simultaneous training. Animals trained on both tasks simultaneously were significantly facilitated in their ability to acquire the trace eyeblink conditioning task; no effect of simultaneous training was seen on the water maze task. No effect was seen on acquisition for either task when using the consecutive training design. Taken together, these findings provide insight into how the hippocampus processes information when animals learn multiple hippocampus-dependent tasks.The importance of the hippocampus in learning is well established (Berger et al. 1976;Berger and Thompson 1978;Disterhoft et al. 1999). A number of studies have demonstrated the necessity of the hippocampus in learning spatial and nonspatial tasks, as well as those requiring the association of temporally remote events (Morris et al. 1982;Moyer Jr. et al. 1990;Davidson and Jarrard 1993;McEchron et al. 1998;Bannerman et al. 1999;Weiss et al. 1999a). Two such tasks are trace eyeblink conditioning (EBC) and Morris water maze (WMZ).A common cellular mechanism that underlies learning, increased membrane excitability, has been observed by several investigators. This mechanism is conserved across species, tasks, and brain regions. Trains of action potentials in both hippocampal and cortical neurons are followed by a prolonged post-burst afterhyperpolarization (AHP), which decreases neuronal excitability and inhibits further firing to a sustained depolarizing input (Schwindt et al. 1988;Storm 1990). A reduction in the AHP occurred in both rat and rabbit CA1 pyramidal neurons after acquisition of trace EBC (Moyer Jr. et al. 1996;Kuo et al. 2004). This reduction also occurred in rat CA1 pyramidal neurons after acquisition of another type of hippocampus-dependent task, the spatial Morris WMZ (Oh et al. 2003). Alterations in the AHP with learning have also been observed in rat piriform cortical neurons after acquisition of an odor discrimination task (Saar et al. 1998). In both hippocampus and piriform cortex, the reduced AHP followed a similar time course after learning, with a maximal reduction 24 h after task acquisition and a return to baseline within 7 d of acquisition (Moyer Jr. et al. 1996;Saar et al. 1998).In a...

Previous work done by our laboratory has demonstrated a reduction of the post-burst afterhyperpolarization (AHP) and accommodation following trace eyeblink conditioning in rabbit CA1 pyramidal neurons. Our laboratory has also demonstrated a reduction in the AHP in rat CA1 pyramidal neurons following spatial learning. In the current study we have extended our findings in rabbits by showing a reduction in both the AHP and accommodation in F344 X BN rat CA1 pyramidal neurons following acquisition of trace eyeblink conditioning. A component current of the AHP, I M , was evaluated with a specific blocker of this current, and showed no apparent contribution to the learning-related increase in neuronal excitability. Rather, a reduction in an isoproterenol-sensitive component of the AHP, presumably sI AHP , was observed to underlie the learning-specific change.