Craig F. Ferris

Regional cerebral blood flow and BOLD responses in conscious and anesthetized rats under basal and hypercapnic conditions: implications for functional MRI studies

Anesthetics, widely used in magnetic resonance imaging (MRI) studies to avoid movement artifacts, could have profound effects on cerebral blood flow (CBF) and cerebrovascular coupling relative to the awake condition. Quantitative CBF and tissue oxygenation (blood oxygen level–dependent [BOLD]) were measured, using the continuous arterial-spin-labeling technique with echo-planar-imaging acquisition, in awake and anesthetized (2% isoflurane) rats under basal and hypercapnic conditions. All basal blood gases were within physiologic ranges. Blood pressure, respiration, and heart rates were within physiologic ranges in the awake condition but were depressed under anesthesia (P < 0.05). Regional CBF was heterogeneous with whole-brain CBF values of 0.86 ± 0.25 and 1.27 ± 0.29 mL · g–1 · min–1 under awake and anesthetized conditions, respectively. Surprisingly, CBF was markedly higher (20% to 70% across different brain conditions) under isoflurane-anesthetized condition compared with the awake state (P < 0.01). Hypercapnia decreased pH, and increased Pco2 and Po2. During 5% CO2 challenge, under awake and anesthetized conditions, respectively, CBF increased 51 ± 11% and 25 ± 4%, and BOLD increased 7.3 ± 0.7% and 5.4 ± 0.4%. During 10% CO2 challenge, CBF increased 158 ± 28% and 47 ± 11%, and BOLD increased 12.5 ± 0.9% and 7.2 ± 0.5%. Since CBF and BOLD responses were substantially higher under awake condition whereas blood gases were not statistically different, it was concluded that cerebrovascular reactivity was suppressed by anesthetics. This study also shows that perfusion and perfusion-based functional MRI can be performed in awake animals.

Neural Connections of the Anterior Hypothalamus and Agonistic Behavior in Golden Hamsters

In male golden hamsters, offensive aggression is regulated by an interaction between arginine-vasopressin and serotonin at the level of the anterior hypothalamus. The present studies were conducted to study a neural network underlying this interaction. The connections of the anterior hypothalamus were examined by retrograde and anterograde tracing in adult male hamsters. Several limbic areas were found to contain both types of tracing suggesting reciprocal connections with the anterior hypothalamus. Their functional significance relating to the consummation of aggression was tested by comparing neuronal activity (examined through quantification of c-Fos-immunolabeling) in two groups of animals. Experimental animals were sacrificed after attacking an intruder. Control animals were sacrificed after exposure to a woodblock carrying the odor of an intruder that elicited behaviors related to offensive aggression without its consummation. An increased density of Fos-immunoreactivity was found in experimental animals within the medial amygdaloid nucleus, ventrolateral hypothalamus, bed nucleus of the stria terminalis and dorsolateral part of the midbrain central gray. These data suggest that these areas are integrated in a neural network centered on the anterior hypothalamus and involved in the consummation of offensive aggression. Finally, c-Fos-immunoreactivity was combined with labeling of serotonin and vasopressin neurons to identify sub-populations particularly associated with offensive aggression. Vasopressin neurons in the nucleus circularis and medial division of the supraoptic nucleus showed increased neuronal activity in the fighters, supporting their role in the control of offensive aggression.

Functional Magnetic Resonance Imaging Shows Oxytocin Activates Brain Regions Associated with Mother–Pup Bonding during Suckling

Oxytocin is released in the maternal brain during breastfeeding and may help strengthen the mother–infant relationship. Here, we used functional magnetic resonance imaging to determine whether oxytocin modulates brain activity in postpartum day 4–8 dams receiving suckling stimulation. During imaging sessions, dams were exposed to pup suckling before and after administration of an oxytocin receptor antagonist. Another group of dams received oxytocin alone. Changes in brain activation in response to suckling closely matched that elicited by oxytocin administration. The overlapping brain areas included the olfactory system, nucleus accumbens, insular cortex, prefrontal cortex, ventral tegmental area, cortical amygdala, and several cortical and hypothalamic nuclei. Blockade of oxytocin receptors largely attenuated activation in these regions. The data suggest that oxytocin may strengthen mother–infant bond formation partly by acting through brain areas involved in regulating olfactory discrimination, emotions, and reward.

Testosterone facilitates aggression by modulating vasopressin receptors in the hypothalamus

In many species, testosterone treatment facilitates offensive aggression tested in resident-intruder models. As the mechanisms of action of testosterone remain unclear, we hypothesized that testosterone interacts with neurotransmitter systems involved in the regulation of offensive aggression. We tested this hypothesis with the vasopressinergic system in golden hamsters in three separate experiments. First, we compared the density of V1 vasopressin (VAP) receptor binding between castrated animals treated with testosterone and their untreated controls. The most noticeable difference was found within the ventrolateral hypothalamus (VLH), a site involved in the control of aggression in several species of mammals. Within this area, V1 AVP receptor binding disappeared after castration, while being maintained by testosterone-treatment. Second, we tested behavioral effects of AVP within the VLH. Microinjections of AVP (100 nl, 1 or 100 microM) within the VLH accelerated the onset of offensive aggression in testosterone-treated animals. However, AVP-injected animals did not bite more than their vehicle-injected controls. Third, microinjections of AVP failed to activate offensive aggression in animals deprived of testosterone. As AVP receptors appeared to overlay previously described distributions of androgen and estrogen receptors in golden hamsters, we propose that testosterone facilitates the onset of offensive aggression, at least partly, through an activation of AVP receptors within the VLH.

Pup Suckling Is More Rewarding Than Cocaine: Evidence from Functional Magnetic Resonance Imaging and Three-Dimensional Computational Analysis

Nursing has reciprocal benefits for both mother and infant, helping to promote maternal behavior and bonding. To test the “rewarding” nature of nursing, functional magnetic resonance imaging was used to map brain activity in lactating dams exposed to their suckling pups versus cocaine. Suckling stimulation in lactating dams and cocaine exposure in virgin females activated the dopamine reward system. In contrast, lactating dams exposed to cocaine instead of pups showed a suppression of brain activity in the reward system. These data support the notion that pup stimulation is more reinforcing than cocaine, underscoring the importance of pup seeking over other rewarding stimuli during lactation.

Procedure for minimizing stress for fMRI studies in conscious rats

Functional magnetic resonance imaging (fMRI) in conscious animals is evolving as a critical tool for neuroscientists. The present study explored the effectiveness of an acclimation procedure in minimizing the stress experienced by the animal as assessed by alterations in physiological parameters including heart rate, respiratory rate, and serum corticosterone levels. Results confirm that as the stress of the protocol is minimized, there is a significant decrease in head movements and enhancement in data quality. The feasibility of improving the quality of fMRI data acquired in alert rats by utilizing a relatively simple technique is presented.

Acute and repeated exposure to social conflict in male golden hamsters : increases in plasma POMC-peptides and cortisol and decreases in plasma testosterone

The purpose of the present study was to characterize the hormonal response of dominant and submissive male hamsters to acute and repeated exposure to social conflict. We found that submissive, but not dominant, males exhibited elevated plasma levels of adrenocorticotropin (ACTH), cortisol, and beta-endorphin (beta-EP) following one exposure to an agonistic encounter. After five exposures to a dominant opponent, submissive males showed smaller, but still significant, elevations in these plasma hormones. After nine exposures, submissive hamsters showed significant elevations only in plasma ACTH and beta-EP. Plasma testosterone was significantly suppressed in submissive males that fought nine times. We conclude that hamsters are a useful species with which to study the neuroendocrine correlates of social behavior.

Serotonin blocks vasopressin-facilitated offensive aggression: Interactions within the ventrolateral hypothalamus of golden hamsters

In golden hamsters, vasopressin (AVP) microinjected within the ventrolateral hypothalamus (VLH) facilitates offensive aggression. As serotonin is known to inhibit offensive aggression, we decided to test whether AVP-facilitated behavior is also inhibited by serotonin treatment. Testosterone-treated male golden hamsters received IP injections of fluoxetine, a serotonin reuptake inhibitor, or vehicle 1 h prior to AVP microinjections within the VLH. The animals were tested for offensive aggression in a resident-intruder model after the microinjections, and the results were compared between groups. Pretreatment with fluoxetine inhibited AVP-facilitated offensive aggression. Only one out of nine fluoxetine-treated animals attacked and bit the intruders, compared to six out of seven vehicle-treated animals. Furthermore, we also confirmed by in vitro autoradiography that the VLH contains vasopressin V(1) and serotonin 5-HT1B receptors. Therefore, it is possible that serotonin may inhibit AVP-facilitated offensive aggression by acting directly at the level of the VLH as well as at other sites.

Dopamine D2-like antagonists induce chromatin remodeling in striatal neurons through cyclic AMP-protein kinase A and NMDA receptor signaling

Antipsychotic drugs regulate gene transcription in striatal neurons by blocking dopamine D2‐like receptors. Little is known about the underlying changes in chromatin structure, including covalent modifications at histone N‐terminal tails that are epigenetic regulators of gene expression. We show that treatment with D2‐like antagonists rapidly induces the phosphorylation of histone H3 at serine 10 and the acetylation of H3‐lysine 14 in bulk chromatin from striatum and in nuclei of striatal neurons. We find that, in vivo, D2‐like antagonist‐induced H3 phospho‐acetylation is inhibited by the NMDA receptor antagonist MK‐801 and by the protein kinase A (PKA) inhibitor Rp‐adenosine 3c′,5c′‐cyclic monophosphorothioate triethylammonium salt but increased by the PKA activator Sp‐adenosine 3c′,5c′‐cyclic monophosphorothioate triethylammonium salt. Furthermore, in dissociated striatal cultures which lack midbrain and cortical pre‐synaptic inputs, H3 phospho‐acetylation was induced by glutamate, l‐type Ca2+ channel agonists and activators of cAMP‐dependent PKA but inhibited by NMDA receptor antagonists or PKA antagonists. The dual modification, H3pS10‐acK14, was enriched at genomic sites with active transcription and showed the kinetics of the early response. Together, these results suggest that histone modifications and chromatin structure in striatal neurons are dynamically regulated by dopaminergic and glutamatergic inputs converging on the cellular level. Blockade of D2‐like receptors induces H3 phospho‐acetylation, H3pS10‐acK14, through cAMP‐dependent PKA, and post‐synaptic NMDA receptor signaling.

Serotonin regulation of aggressive behavior in male golden hamsters (Mesocricetus auratus).

These studies examined the neurochemistry and neuroanatomy of the serotonin (5-HT) system innervating the anterior hypothalamus (AH) and the interaction of 5-HT receptor agonists with arginine vasopressin (AVP) in the regulation of offensive aggression in golden hamsters. Because specific 5-HT1A, 5-HT1B, and AVP V1A binding sites were observed within the AH by in vitro autoradiography, the hamsters were tested for offensive aggression after microinjections of AVP in combination with either the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetraline (DPAT) or the 5-HT1B agonist CGS-12066A (CGS) directly within the AH. Though treatment with DPAT resulted in a dose-dependent inhibition of AVP-facilitated offensive aggression, CGS was ineffective. In addition, a retrograde tracer was injected within the AH to localize the distribution of 5-HT neurons projecting to the area. Retrogradely labeled 5-HT neurons were found within the dorsal, median, and caudal linear raphe nuclei and are suspected to inhibit AVP-facilitated offensive aggression by an activation of 5-HT1A receptors in the AH.