Embryonic ethanol exposure induces ectopic Hcrt and MCH neurons outside hypothalamus in rats and zebrafish: Role in ethanol‐induced behavioural disturbances

Abstract

Embryonic exposure to ethanol increases the risk for alcohol use disorder in humans and stimulates alcohol‐related behaviours in different animal models. Evidence in rats and zebrafish suggests that this phenomenon induced by ethanol at low‐moderate concentrations involves a stimulatory effect on neurogenesis and density of hypothalamic neurons expressing the peptides, hypocretin/orexin (Hcrt) and melanin‐concentrating hormone (MCH), known to promote alcohol consumption. Building on our report in zebrafish showing that ethanol induces ectopic expression of Hcrt neurons outside the hypothalamus, we investigated here whether embryonic ethanol exposure also induces ectopic peptide neurons in rats similar to zebrafish and affects their morphological characteristics and if these ectopic neurons are functional and have a role in the ethanol‐induced disturbances in behaviour. We demonstrate in rats that ethanol at a low‐moderate dose, in addition to increasing Hcrt and MCH neurons in the lateral hypothalamus where they are normally concentrated, induces ectopic expression of these peptide neurons further anterior in the nucleus accumbens core and ventromedial caudate putamen where they have not been previously observed and causes morphological changes relative to normally located hypothalamic neurons. Similar to rats, embryonic ethanol exposure at a low‐moderate dose in zebrafish induces ectopic Hcrt neurons anterior to the hypothalamus and alters their morphology. Notably, laser ablation of these ectopic Hcrt neurons blocks the behavioural effects induced by ethanol exposure, including increased anxiety and locomotor activity. These findings suggest that the ectopic peptide neurons are functional and contribute to the ethanol‐induced behavioural disturbances related to the overconsumption of alcohol.

The Impact of Prenatal Alcohol Exposure on the Autonomic Nervous System and Cardiovascular System in Rats in a Sex-Specific Manner

“…The cardiovascular function of the female offspring population seems to be more noticeably affected by PAE. It should be noted that such observations were made regardless of the applied PAE protocol [ 33 , 34 , 35 ]. The PAE model as described by Thomas et al was used with modifications [ 19 ].…”

Role of Chemokine Cxcl12a in Mediating the Stimulatory Effects of Ethanol on Embryonic Development of Subpopulations of Hypocretin/Orexin Neurons and Their Projections

“…For example, Hcrt neurons co-express other neurochemicals such as dynorphin and glutamate [36,71], and it is possible that embryonic ethanol exposure or Cxcl12a overexpression alters their level of co-expression within specific subpopulations of Hcrt neurons that in turn affect neuronal functioning and contribute to behavioral disturbances. Our laboratory recently demonstrated the functional importance of specific Hcrt subpopulations in mediating ethanol-induced behaviors [7], showing that ablation of the ectopic POA Hcrt neurons or the Hcrt neurons in the most anterior part of the aAH blocks the ethanol-induced increase in anxiety-like behavior, and ablation of the ectopic Hcrt neurons blocks the ethanol-induced increase in locomotor behavior. In this report, we take the next step and reveal that Cxcl12a is involved in mediating the ethanol-induced effects on the projections of different Hcrt neuron subpopulations to functionally different brain areas.…”

“…These effects are also brain-area dependent, with ethanol increasing the number, length and complexity of projections from neurons in the hippocampus [19] while decreasing these measures from neurons in the prefrontal cortex [20,21]. We recently found in both rats and zebrafish that ethanol increases the number of processes emanating from the soma of normally located Hcrt neurons [7]. Further, while having little effect on the short projections from Hcrt neurons to local regions, ethanol in zebrafish stimulates the long descending projections from pAH Hcrt neurons that innervate the locus coeruleus (LC) and the long ascending projections from aAH Hcrt neurons that become ectopically expressed in the POA and innervate the subpallium (SP) and dorsal pallium (DP) [9].…”

“…Studies in rodent models show that prenatal exposure to ethanol at low-moderate concentrations stimulates neuronal development, increasing the proliferation, neurogenesis and migration of neurons expressing the hypothalamic peptide, hypocretin/orexin (Hcrt) [3][4][5][6]. This stimulatory effect on peptidergic neurons is shown in rats to be anatomically specific, with ethanol increasing the number of enkephalin-expressing neurons in the core but not shell of the nucleus accumbens (NAc) [5] and also causing Hcrt neurons to be ectopically expressed outside the hypothalamus, further anterior in the NAc core and ventromedial caudate putamen [7].…”

“…In zebrafish embryos and larvae, embryonic ethanol exposure at a low-moderate dose (0.5% v/v) in the water increases the number of Hcrt neurons in the anterior hypothalamus (AH) in an area-dependent manner, specifically in the most anterior (aAH) but not posterior (pAH) region of the AH [9,10]. Ethanol also causes some of these aAH neurons in zebrafish to migrate further anterior and to be ectopically expressed in the preoptic area (POA) [7,11], consistent with other zebrafish studies showing ethanol inducing ectopically located oxytocin neurons and facial branchial motor neurons [12,13]. The induction of these ectopic neurons is likely due to ethanol's effects on the timing and directionality of neuronal migration [4,12,14], resulting in their clustering at inappropriate sites that leads to the formation of heterotopias [15], a phenomenon observed in the brains of children with fetal alcohol spectrum disorders [16].…”