A rat model of pre-puberty (juvenile) stress-induced predisposition to stress-related disorders: sex similarities and sex differences in effects and symptoms.

OBJECTIVES: This study assessed the interactive effect of two risk factors: "Juvenile stress" and sex in the long-term consequences of "Juvenile stress" in male and female rats. METHODS: Rats were exposed to "Juvenile stress" and to additional stress in adulthood. Measurements of anxiety and depressive-like behaviours were assessed in relation to each stress exposure and "Sex-specific" sets of criteria in order to characterize individual profiles of altered behaviours. RESULTS: While both male and female rats were affected by exposure to "Juvenile stress", sex difference were evident in saccharine preference, coping with the stressful challenge of the two-way shuttle avoidance task, and on "Adult stress" induced changes in saccharine preference. "Profiling" altered behaviours revealed sex differences also in the prevalence of rats exhibiting different categories of "Affected" behaviours, indicating that female rats are more susceptible to the long-term effects of "Juvenile stress" and to the immediate effects of "Adulthood stress". Additionally, the prevalence of "Affected" animals among "Juvenile+ Adulthood stress" was similar, yet the profile of altered behaviours was significantly different. CONCLUSIONS: The "Behavioural Profiling" approach presented here is of importance to understanding gender differences in the aetiology of predisposition to stress-related disorders, and of gender symptomatology differences in stress-related disorders.

Tryptophan hydroxylase genotype is associated with impulsive-aggression measures: a preliminary study.

To assess the relationship between two phenotypes in an extremely well-characterized population of personality disorder patients-impulsive aggression and prolactin response to fenfluramine-and tryptophan hydroxylase (TPH) genotype, TPH genotype (at an intronic polymorphic site) and prolactin response to fenfluramine were assessed in 40 Caucasian patients with personality disorder. Impulsive aggression was assessed by using the Buss-Durkee Hostility Inventory (BDHI). Twenty-one male patients with the "LL" genotype had higher BDHI scores than men with the "UL" or the "UU" genotype. No relationship between genotype and prolactin response to fenfluramine was found. It was concluded that impulsive-aggressive behavior in male personality disorder patients may be associated with the TPH genotype.

Analysis of sequence-dependent interactions between transient calcium and transmitter stimuli in activating adenylyl cyclase in Aplysia: possible contribution to CS--US sequence requirement during conditioning.

An important recent insight in a number of neurobiological systems is that during learning, individual dually regulated proteins with associative properties function as critical sites of stimulus convergence. During conditioning in Aplysia, the Ca2+ /calmodulin-sensitive adenylyl cyclase (AC) in mechanosensory neurons serves as a molecular site of interaction between Ca2+ and serotonin [5-hydroxytryptamine (5-HT)]-two signals that represent the CS and US in these cells. Conditioning requires that the CS and US be paired within a narrow time window and in the appropriate sequence. AC shows an analogous sequence preference: It is more effectively activated when a pulse of Ca2+ precedes a pulse of 5-HT than when the 5-HT precedes Ca2+. One mechanism that contributes to this sequence preference is that Ca2+/calmodulin binding to AC accelerates the rate of AC activation by receptor-Gs. We have identified two additional properties of AC activation that would cause pairing with Ca2+ preceding 5-HT to be more effective than simultaneous pairing or pairing with the reciprocal sequence: (1) Activation of Aplysia AC by a Ca2+ pulse rose with a delay compared with activation by a 5-HT pulse. (2) A late pulse of Ca2+, which arrived after 5-HT, acted, via calmodulin, to accelerate the decay of AC activation by receptor-Gs. Together, these activation properties of AC may contribute to the CS-US sequence requirement of classical conditioning.

Hearing loss and asymmetry in major depression.

To assess patterns of hearing loss and asymmetry in major depressive disorder (MDD), pure-tone and brief-click audiometric thresholds were measured in 59 inpatients with MDD and 40 normal control subjects. For both tasks, patients had higher bilateral thresholds, with marked hearing loss for the highest pure-tone frequency. At lower frequencies, patients displayed significant asymmetry, with poorer hearing in the left ear. After ECT, patients maintained the bilateral hearing losses; however, the baseline asymmetry resolved. These findings suggest that bilateral hearing loss may be a stable characteristic in severe depression. Poorer left ear pure-tone hearing may be present during the depressed state. The baseline asymmetry in audiometric deficits suggests right-hemisphere dysfunction in severe MDD.

A quantitative study of the Ca2+/calmodulin sensitivity of adenylyl cyclase in Aplysia, Drosophila, and rat.

Studies in Aplysia and Drosophila have suggested that Ca2+/calmodulin-sensitive adenylyl cyclase may act as a site of convergence for the cellular representations of the conditioned stimulus (Ca2+ influx) and unconditioned stimulus (facilitatory transmitter) during elementary associative learning. This hypothesis predicts that the rise in intracellular free Ca2+ concentration produced by spike activity during the conditioned stimulus will cause an increase in the activity of adenylyl cyclase. However, published values for the Ca2+ sensitivity of Ca2+/calmodulin-sensitive adenylyl cyclase in mammals and in Drosophila vary widely. The difficulty in evaluating whether adenylyl cyclase would be activated by physiological elevations in intracellular Ca2+ levels is in part a consequence of the use of Ca2+/EGTA buffers, which are prone to several types of errors. Using a procedure that minimizes these errors, we have quantified the Ca2+ sensitivity of adenylyl cyclase in membranes from Aplysia, Drosophila, and rat brain with purified species-specific calmodulins. In all three species, adenylyl cyclase was activated by an increase in free Ca2+ concentration in the range caused by spike activity. Ca2+ sensitivity was dependent on both calmodulin concentration and Mg2+ concentration. Mg2+ raised the threshold for adenylyl cyclase activation by Ca2+ but also acted synergistically with Ca2+ to activate maximally adenylyl cyclase.

Temporal asymmetry in activation of Aplysia adenylyl cyclase by calcium and transmitter may explain temporal requirements of conditioning.

Cellular experiments have suggested that during classical conditioning of the gill and siphon withdrawal reflex of Aplysia, adenylyl cyclase may serve as a molecular site of convergence for Ca2+ and serotonin (5-hydroxytryptamine; 5-HT), the cellular representations of the conditioned and unconditioned stimuli (CS and US). We explored the possible molecular basis of the behavioral requirement that the CS and US be paired within a narrow time window and in the appropriate order. To examine the temporal interactions of brief pulses of Ca2+ and 5-HT in stimulating Aplysia neural cyclase, we used a perfused-membrane cyclase assay. When brief pulses of Ca2+ and 5-HT were paired, cyclase activation depended upon the sequence of the pulses: peak cyclase activation was greater when the Ca2+ pulse immediately preceded the 5-HT pulse. Examination of the rising phase of 5-HT stimulation suggested that a Ca2+ prepulse might accelerate the onset of activation by 5-HT, without affecting the final level of activation achieved with prolonged 5-HT exposure. The observed interactions between Ca2+ and transmitter in activating cyclase could contribute importantly to the temporal requirements of conditioning for CS-US pairing.

Biochemical correlates of short-term sensitization in Aplysia: temporal analysis of adenylate cyclase stimulation in a perfused-membrane preparation.

During short-term sensitization, a simple form of nonassociative learning in Aplysia, the presentation of a single brief noxious stimulus results in enhancement of the defensive withdrawal reflex lasting minutes to tens of minutes. This behavioral plasticity involves presynaptic facilitation of synaptic transmission from the mechanosensory neurons that mediate the reflex to their central target cells. This facilitation is due to cAMP-dependent protein phosphorylation. To determine whether the time course of presynaptic facilitation might be due to a persistent increase in activity of adenylate cyclase (EC 4.6.1.1) itself, persistence of the transmitter, or yet other processes, we developed a perfused-membrane method to analyze the time course of activation of adenylate cyclase by transient stimuli. After stimulation by a pulse of stimulatory transmitter, activation of adenylate cyclase decayed within 60 sec. This finding indicates that the enzyme does not remain persistently active in the absence of transmitter and suggests that short-term retention is likely to be due to other mechanisms. Possible additional mechanisms include continued activation of the cyclase by transmitter, cellular factors extrinsic to the cyclase that prolong the time course of its activation, and persistence of processes downstream from the cyclase.

Possible involvement of adenylate cyclase in learning and short-term memory. Experimental data and some theoretical considerations.

Two experimental approaches--the cellular and the neurogenetic--to the study of molecular mechanisms of elementary memory implicate the cyclic AMP cascade in general, and adenylate cyclase in particular, in the processes of acquisition and short-term memory. Models of learning and memory should account for four basic phenomena: persistence of memory, stimulus convergence, temporal specificity and memory decay. These phenomena thus place constraints on the structure and operation of any postulated memory apparatus. The relevant experimental data derived from the study of memory mutants in Drosophila and of the gill and siphon withdrawal reflex in Aplysia are discussed and analyzed in light of the above mentioned constraints.

Defective responsiveness of adenylate cyclase to forskolin in the Drosophila memory mutant rutabaga.

The Drosophila memory mutant rutabaga (rut) has been previously shown to have a defective subpopulation (or functional state) of the enzyme adenylate cyclase. We report here that the reduced adenylate cyclase activity is also associated with a defective responsiveness of the enzyme to forskolin. Forskolin activation isotherms of the enzyme in normal membranes reveal low- and high-affinity forskolin-interacting components; the residual enzyme in the mutant shows a smaller proportion of the high-affinity response. In addition, in mutant membrane preparations, forskolin fails to shift the Km of the enzyme for free Mg2+ and for MgATP, in contrast to the situation in the normal tissue. The defect in the responsiveness to forskolin in rut is even more pronounced in a Lubrol-solubilized enzyme preparation, and is due to intrinsic properties of the cyclase system rather than to the absence (or presence) of a soluble, or detergent solubilized, factor in rut. The reduced forskolin responsiveness maps to the X chromosomal segment 12F5-6 to 13A1-5, within the region previously reported to span the locus that controls both the abortive memory and the lack of Ca2+-stimulation of adenylate cyclase in rut17. The possible relevance of the findings to postulated molecular mechanisms of short-term memory formation is discussed.