Taming in the wild Norway rat following lesions in the basal ganglia

Identification of retinal ganglion cell types and brain nuclei expressing the transcription factor Brn3c/Pou4f3 using a Cre recombinase knock-in allele

Members of the POU4F/Brn3 transcription factor family have an established role in the development of retinal ganglion cell (RGCs) types, the main transducers of visual information from the mammalian eye to the brain. Our previous work using sparse random recombination of a conditional knock-in reporter allele expressing alkaline phosphatase (AP) and intersectional genetics had identified three types of Brn3c positive (Brn3c⁺ ) RGCs. Here, we describe a novel Brn3c^Cre mouse allele generated by serial Dre to Cre recombination and use it to explore the expression overlap of Brn3c with Brn3a and Brn3b and the dendritic arbor morphologies and visual stimulus response properties of Brn3c⁺ RGC types. Furthermore, we explore brain nuclei that express Brn3c or receive input from Brn3c⁺ neurons. Our analysis reveals a much larger number of Brn3c⁺ RGCs and more diverse set of RGC types than previously reported. Most RGCs expressing Brn3c during development are still Brn3c positive in the adult, and all express Brn3a while only about half express Brn3b. Genetic Brn3c-Brn3b intersection reveals an area of increased RGC density, extending from dorsotemporal to ventrolateral across the retina and overlapping with the mouse binocular field of view. In addition, we report a Brn3c⁺ RGC projection to the thalamic reticular nucleus, a visual nucleus that was not previously shown to receive retinal input. Furthermore, Brn3c⁺ neurons highlight a previously unknown subdivision of the deep mesencephalic nucleus. Thus, our newly generated allele provides novel biological insights into RGC type classification, brain connectivity, and cytoarchitectonic.

A Central Amygdala-Globus Pallidus Circuit Conveys Unconditioned Stimulus-Related Information and Controls Fear Learning

The central amygdala (CeA) is critically involved in a range of adaptive behaviors, including defensive behaviors. Neurons in the CeA send long-range projections to a number of extra-amygdala targets, but the functions of these projections remain elusive. Here, we report that a previously neglected CeA-to-globus pallidus external segment (GPe) circuit plays an essential role in classical fear conditioning. By anatomic tracing, in situ hybridization and channelrhodopsin (ChR2)-assisted circuit mapping in both male and female mice, we found that a subset of CeA neurons send projections to the GPe, and the majority of these GPe-projecting CeA neurons express the neuropeptide somatostatin. Notably, chronic inhibition of GPe-projecting CeA neurons with the tetanus toxin light chain (TeLC) completely blocks auditory fear conditioning. In vivo fiber photometry revealed that these neurons are selectively excited by the unconditioned stimulus (US) during fear conditioning. Furthermore, transient optogenetic inactivation or activation of these neurons selectively during US presentation impairs or promotes, respectively, fear learning. Our results suggest that a major function of GPe-projecting CeA neurons is to represent and convey US-related information through the CeA-GPe circuit, thereby regulating learning in fear conditioning.SIGNIFICANCE STATEMENT The central amygdala (CeA) has been implicated in the establishment of defensive behaviors toward threats, but the underlying circuit mechanisms remain unclear. Here, we found that a subpopulation of neurons in the CeA, which are mainly those that express the neuropeptide somatostatin, send projections to the globus pallidus external segment (GPe), and this CeA-GPe circuit conveys unconditioned stimulus (US)-related information during classical fear conditioning, thereby having an indispensable role in learning. Our results reveal a previously unknown circuit mechanism for fear learning.

Top down control of spinal sensorimotor circuits essential for survival

The ability to interact with challenging environments requires coordination of sensory and motor systems that underpin appropriate survival behaviours. All animals, including humans, use active and passive coping strategies to react to escapable or inescapable threats, respectively. Across species the neural pathways involved in survival behaviours are highly conserved and there is a consensus that knowledge of such pathways is a fundamental step towards understanding the neural circuits underpinning emotion in humans and treating anxiety or other prevalent emotional disorders. The midbrain periaqueductal grey (PAG) lies at the heart of the defence-arousal system and its integrity is paramount to the expression of survival behaviours. To date, studies of 'top down control' components of defence behaviours have focused largely on the sensory and autonomic consequences of PAG activation. In this context, effects on motor activity have received comparatively little attention, despite overwhelming evidence of a pivotal role for the PAG in coordinating motor responses essential to survival (e.g. such as freezing in response to fear). In this article we provide an overview of top down control of sensory functions from the PAG, including selective control of different modalities of sensory, including proprioceptive, information forwarded to a major supsraspinal motor control centre, the cerebellum. Next, evidence from our own and other laboratories of PAG control of motor outflow is also discussed. Finally, the integration of sensorimotor functions by the PAG is considered, as part of coordinated defence behaviours that prepare an animal to be ready and able to react to danger.

Análise crítica dos sistemas neurais envolvidos nas respostas de medo inato

O nosso entendimento das bases neurofisiológicas da reação emocional do medo baseia-se em grande parte nos estudos que envolvem respostas condicionadas a estímulos fisicamente aversivos, como, por exemplo, o choque elétrico nas patas. Enquanto este paradigma parece ser útil para avaliarmos os sistemas neurais envolvidos na resposta do, assim chamado, medo condicionado (que tipicamente tem se limitado à observação da resposta de congelamento), este paradigma parece ter sérias limitações para investigarmos as bases neurais das respostas de medo em circunstancias naturais. Trabalhos recentes utilizando técnicas de lesões neurais bem como de mapeamento funcional em animais expostos a predadores naturais, ou somente ao odor destes predadores, revelam uma série de estruturas neurais como responsáveis pelas respostas de medo inato, bastante distintas daquelas previamente implicadas nas respostas de condicionamento aversivo. Como revisto no presente trabalho, entre estas estruturas temos distritos diferenciados da zona medial do hipotálamo; setores específicos da amídala e do sistema septo-hipocampal, envolvidos, respectivamente no processamento de pistas relacionadas à presença do predador e na análise contextual do ambiente; e setores da matéria cinzenta periaquedutal, já classicamente envolvidos na expressão de respostas de defesa. Estas informações podem ser potencialmente importantes para a análise e terapêutica de psicopatologias relacionadas aos distúrbios da reação emocional de medo.

Superior colliculus projections to midline and intralaminar thalamic nuclei of the rat

The superior colliculus (SC) projections to the midline and intralaminar thalamic nuclei were examined in the rat. The retrograde tracer cholera toxin beta (CTb) was injected into one of the midline thalamic nuclei-paraventricular, intermediodorsal, rhomboid, reuniens, submedius, mediodorsal, paratenial, anteroventral, caudal ventromedial, or parvicellular part of the ventral posteriomedial nucleus-or into one of the intralaminar thalamic nuclei-medial parafascicular, lateral parafascicular, central medial, paracentral, oval paracentral, or central lateral nucleus. After 10-14 days, the brains from these animals were processed histochemically, and the retrogradely labeled neurons in the SC were mapped. The lateral sector of the intermediate gray and white layers of the SC send axonal projections to the medial and lateral parafascicular, central lateral, paracentral, central medial, rhomboid, reuniens, and submedius nuclei. The medial sector of the intermediate and deep SC layers project to the parafascicular and central lateral thalamic nuclei. The paraventricular thalamic nucleus is innervated almost exclusively by the medial sectors of the deep SC layers. The superficial gray and optic layers of the SC do not project to any of these thalamic areas. The discussion focuses on the role these SC-thalamic inputs may have on forebrain circuits controlling orienting and defense (i.e., fight-or-flight) reactions.

Behaviors of rats with insidious, multifocal brain damage induced by seizures following single peripheral injections of lithium and pilocarpine

Several domains of behavior were measured in rats (n = 465) 10 days to 100 days after induction of limbic seizures by a single subcutaneous injection of lithium and pilocarpine. These rats displayed enhanced intragroup aggression but normal muricide; gustatory neophobia and conditioned taste aversion were virtually eliminated. Severe working and reference memory deficits were evident within the radial arm maze. Both state-dependent memory and possible situation-dependent precipitation of spontaneous seizures were suggested. The behavioral changes were considered commensurate with the multifocal pattern of thalamic, hippocampal/amygdaloid, and limbic cortical damage.

Subtotal lesions of the amygdala: the rostral central nucleus in passive avoidance and ulceration

Rats received small bilateral electrolytic or ibotenate lesions of the rostral part of the amygdaloid central (rACE) or lateral (rAL) nuclei, or caudal part of the basolateral nuclei (cBL), or electrolytic lesions of the dorsal hippocampus (HIPP). All groups were tested in a drinking passive avoidance (PA) task that appears less sensitive to deficits in acquisition/retention or activity/spatial perception than are many other PA tasks, and more specifically sensitive to deficits in generation of fear. Consistent with this interpretation, performance in the task was facilitated, not deficient, in the HIPP group. Electrolytic lesions of rAL produced a mild deficit in PA, but ibotenate lesions did not, and neither did the more caudal lesions of the cBL groups. Ibotenate lesions of rACE did produce a deficit in PA, consistent with views of a role of this part of the amygdala in fear. Electrolytic lesions of rACE produced a very profound PA deficit and also blocked the rapid development of gastric erosions by water-restraint stress, effects that were not found with ibotenate lesions in this location. This suggests a particular contribution of fibers passing through rACE to some of the more marked effects of electrolytic lesions of rostrodorsal portions of the amygdala.

Effects of regional amygdaloid lesions on flight and defensive behaviors of wild black rats (Rattus rattus)

Flight and defensive behaviors of wild black rats (R. rattus) in response to nonpainful threatening stimuli were examined before and after regional amygdaloid lesions. Striking disruption of flight was found following damage to all major amygdaloid regions. In contrast, reduced defensiveness was most consistently associated with damage to cortical and, perhaps, central nuclei. The diffuse organization of flight behavior may result from extensive modality-specific cortical afferents to the amygdala and the varied provided by naturalistics threats. The more restricted representation of defensive attack may have resulted from diminished responsiveness to vibrissal stimulation mediated by medial and dorsomedial amygdaloid structures.

Effects of scopolamine on antipredator defense reactions in wild and laboratory rats

Two experiments were designed to investigate the effects of scopolamine hydrobromide (0.25-1.0 mg/kg), and its methyl derivative, on the defensive reactions of rats to nonpainful threat stimuli. In the first experiment, over the dose range studied neither compound significantly altered avoidance, freezing, defensive threat or attack in wild Rattus rattus confronted by the experimenter and other predator-related stimuli. Scopolamine hydrobromide did, however, produce a dose-dependent increase in flight distance; this effect was not seen with the methyl compound, confirming central cholinergic mediation. In the second experiment, no dose of either compound significantly altered the behaviour of Long-Evans rats prior to cat exposure. During cat exposure, however, scopolamine hydrobromide (but not methyl scopolamine) increased the amount of time spent in the vicinity of the cat, increased scanning and rearing, and reduced grooming behaviour. Although reliable, the latter effects were not pronounced. Together, these data do not support a major involvement of central muscarinic receptor mechanisms in the regulation of defensive patterns in wild or laboratory rats.

Attenuation of defensive threat and attack in wild rats (Rattus rattus) by benzodiazepines

A battery of tests designed to elicit reactions to a variety of non-painful threat stimuli was used to study the effects of chlordiazepoxide (5-20 mg/kg), diazepam (1-5 mg/kg) and midazolam (1-10 mg/kg) on the defensive repertoire of wild Rattus rattus. The most consistent effect of benzodiazepine treatment, across compounds and tests, was a marked reduction in defensive threat and attack behaviors, with midazolam effective over a wider range of situations. In contrast, effects on freezing and flight reactions were more variable, differing substantially as a function of stimulus context. The general profile of observed changes in defense cannot be explained in terms of either non-specific behavioral suppression or a global reduction in defensiveness. Rather, our findings suggest that benzodiazepines may primarily induce a shift within the defense repertoire.

'Taming' of wild rats (Rattus rattus) by 5HT1A agonists buspirone and gepirone

A battery of tests designed to elicit reactions to a variety of nonpainful threat stimuli was used to study the effects of the 5HT1A agonists buspirone (5-20 mg/kg), and gepirone (5-20 mg/kg) on the defensive repertoire of wild Rattus rattus. These two compounds produced very similar patterns of results on the test battery, with gepirone generally more effective: Both compounds failed to interfere with either spontaneous motor activity or avoidance/flight to an approaching experimenter. However, both reduced defensive reactivity to proximal threat stimuli, increasing passive contacts with the experimenter in an inescapable situation and reducing "proximal" defensive reactions: jump/flinch reactions to dorsal contact, and, boxing, and biting to a number of threat stimuli. Defensive threat vocalizations and jump attacks were also reduced, but less consistently, as was the experimenter's rating of subject's defensiveness to being picked up. This pattern of results suggested specific "taming" effects of buspirone and, especially, gepirone on defensive reactions. In combination with findings indicating somewhat different (benzodiazepines) to very different (ethanol) profiles for other anxiolytics in the same test battery, these results suggest that the Defense Test Battery may be capable of providing behavioural differentiation among various classes of anxiolytics.

Life-span studies of dominance and aggression in established colonies of laboratory rats

Six mixed-sex colonies of Long-Evans rats were observed at 100-day intervals from colony formation at 100 days of age until all colony members died. Long-term stable dominance relations were observed among males in four colonies while two colonies which had low initial levels of aggression continued to show low intracolony conflict at all ages and no clear dominance relationships. Agonistic interactions among females and between males and females were relatively infrequent and no dominance hierarchy among females was apparent. The aggression of resident males toward intruders increased from 201-601 days of age, but declined overall at age 701. Nevertheless, older males which fought intruders did so as readily as they had when they were young and the few animals that reached 800 days of age continued to attack intruders. Although no systematic decline in total duration or intensity of offense was found across age, there was some evidence of impaired motor performance by older males.

Effects of septal-forebrain lesions on maternal aggression and maternal care

Septal-forebrain lesions significantly increased the defensive reactions of lactating Long-Evans rats (n = 13) relative to nonlesioned control females. The lesions greatly enhanced defensive behaviors on a number of standard tests (e.g., responsiveness to humans and anesthetized conspecifics) while abolishing aggression toward intruding male conspecifics. The lesions also produced a striking disruption in maternal behavior as evidenced by absence of nest building, reduced litter weights, failure to retrieve, lick, or nurse pups, and increased cannibalization. While these results cannot be interpreted as indicating that maternal aggression is equivalent to offense, they are congruent with such a view. Certainly they are not supportive of a view that maternal aggression is primarily defensive. The lesion-induced abolition of maternal attack may have resulted from an inhibition of offensive tendencies by heightened defensiveness and/or reduced pup stimulation. There was no evidence that the lesion-induced impairment in maternal behavior resulted from a failure to sequence the individual behavioral acts comprising maternal behavior. Rather, all features of maternal care seemed to be greatly attenuated.

Reduction of neophobia in mice following lesions of the caudate-putamen

Electrolytic lesions of the caudate-putamen result in a significant decrease in neophobic responses in mice towards a novel object introduced into their familiar environment; however, preference for a novel environment was not altered by the lesion. These data provide a parallel between the effects of lesions of the caudate-putamen and the well-known "amygdala-lesion-syndrome." It is suggested that the striatal complex, which receives massive afferent projection systems, plays a crucial role in sensory-motor integration processes which allow the animals to adapt their responses towards biological significant stimuli in order to cope with their environment.

Ethanol changes patterns of defensive behavior in wild rats

Wild-trapped R. rattus under saline or four ethanol doses were run in tasks designed to measure a range of defensive reactions to nonpainful threat stimuli. Results suggest that at higher doses (1.2 g/kg and above) ethanol reduces defense, with effects ranging from slight reductions to near abolition, depending on the behavior measured. Low and moderate ethanol (0.3 and 0.6 g/kg) doses, however, had divergent effects, tending to enhance components of the defensive attack pattern (vocalization, jump attacks, bites), while not altering other aspects of defensiveness. This pattern of results suggest that an ethanol-based potentiation of defensive attack may be one of the factors involved in the phenomenon of aggression increases following alcohol consumption.

Fluprazine hydrochloride does not decrease defensive behaviors of wild and septal syndrome rats

Recent studies indicate that fluprazine hydrochloride reduces offensive attack in laboratory rats and mice without decreasing defensive behavior during conspecific encounters. Since wild rats and rats displaying the "septal lesion syndrome" show much more pronounced defensive reactions than do normal laboratory rats, these animals were used to provide a more critical test of fluprazine's effectiveness on defense. When a dose of fluprazine hydrochloride (8 mg/kg), previously shown to be highly effective in reducing or eliminating offense, was given to wild and septal syndrome rats these animals showed no reliable decrement in a wide range of defensive reactions including biting attack (defensive attack) to human handling and other stimulation. These findings support the view that fluprazine does not appreciably affect defensive attack or other defensive behaviors even though it strongly inhibits offensive attack.

Taming in wild rats following medial amygdaloid lesions

Flight behavior, startle reactions, and defensiveness to nonpainful stimuli were examined before and after medial amygdaloid lesions in wild Rattus norvegicus and R. rattus. Lesions which included bilateral damage to the medial nucleus strongly reduced defensiveness but had no effect on flight behavior. In contrast, damage to nearby medial structures, which spared the medial nucleus, had no effect on defensiveness but reduced flight behavior. All lesions produced a transient decrease in activity but had no effect on startle reactions. The results suggest a differential organization of flight and defense behavior within the medial amygdala.